Progress in regulated emissions of ethanol-gasoline blends from a

Biofuels

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Progress in regulated emissions of ethanolgasoline blends from a spark ignition engine Amit Kumar Thakur & Ajay Kumar Kaviti To cite this article: Amit Kumar Thakur & Ajay Kumar Kaviti (2018): Progress in regulated emissions of ethanol-gasoline blends from a spark ignition engine, Biofuels, DOI: 10.1080/17597269.2018.1464875 To link to this article: https://doi.org/10.1080/17597269.2018.1464875

Published online: 28 May 2018.

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BIOFUELS, 2018 https://doi.org/10.1080/17597269.2018.1464875

Progress in regulated emissions of ethanol-gasoline blends from a spark ignition engine Amit Kumar Thakura and Ajay Kumar Kavitib a Department of Mechanical Engineering, Dev Bhoomi Institute of Technology, Dehradun, India; bDepartment of Mechanical Engineering, VNRVJIET, Hyderabad, India

ABSTRACT

ARTICLE HISTORY

One of the major sources of increased air pollution is the continuous and rigorous emissions from gasoline engines, which are generating a threat to our environment. Different methods are explored to reduce these emissions. Emissions are formed due to the incomplete combustion of fuel caused by the lack of oxygen content during combustion. Gasoline has no oxygen content so oxygen for the combustion process for a gasoline engine is derived from the intake air, resulting in incomplete combustion; however, additional oxygen can be supplied through ethanol blended with gasoline. Ethanol has the additional advantage of reducing harmful emissions when used a fuel in a spark ignition (SI) engine. On altering the fuel blending ratio in varying percentages the harmful emissions can be checked, which demonstrates the potential of using ethanol-gasoline blends. The aim of this review is to study and analyze the range of opportunities and future prospects for introducing blends of gasoline-ethanol, gasoline with all other alcohols, and derivative and subsequent alternative fuels in varying percentage ratios in existing SI engines by diagnosing various aspects such as air-fuel ratio, operating cylinder pressure, ignition timing and compression ratio related to the emission parameters only.

Received 17 January 2018 Accepted 28 March 2018

Introduction The reserves of petroleum-based fuels are directly correlated with the increasing demand of human mankind for energy production. With the growing world population, industries, vehicles and equipment, the increasing energy demand has led to a search for petroleum fuel substitutes which can cater to the needs of people today. Considering the current global economic crisis, the interest in alternative fuels is extremely high [1]. Air pollution is constantly increasing at a fast pace and is considered a major area of concern for all developed countries. Exhaust emissions from automobiles play the main role in this increased air pollution. Without changing the structure of engines, alternative fuels can be used to figure out low emissions from spark ignition (SI) engines, which gives us food for thought to keep exploring the various possibilities for extracting alternative fuels from various sources. In this quest, ethanol has emerged as the best suited fuel for SI engines in terms of low emissions [2]. The by-products which are generated during the combustion of fuel in engines are known as emissions. Emissions comprises carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), and oxides of nitrogen (NOx) which are called regulated emissions, whereas particulates, formaldehyde, etc. are considered non-regulated emissions. Gasoline, as a

CONTACT Ajay Kumar Kaviti

[email protected]

© 2018 Informa UK Limited, trading as Taylor & Francis Group

KEYWORDS

Ethanol; gasoline; emissions; SI engine

compound hydrocarbon, is not a particularly cleanburning fuel. Lower molecular mass alcohols, in comparison, burn nearly pollution-free. Alcohols already contain oxygen integrated with the fuel, which can lead to more homogeneous combustion. Alcohols burn with a faster flame speed than gasoline, and they do not contain additional elements such as sulfur and phosphorus. All these factors work in the favor of lower molecular mass alcohols with regard to emissions [3]. Due to the continuous change in the composition of gasoline and alternate fuels, it becomes extremely important to comprehend the impacts of new fuels on exhaust emissions. Various studies have been carried out to study the impact of ethanol on exhaust emissions. Studies of gasoline with ethanol contents of 10% or less have generally shown that emissions of CO and unburned HC are reduced with increasing ethanol content. A small increase in NOx emissions is sometimes found with additional ethanol content, but this result is not consistent among studies [4]. Pollutant emissions from fossils fuels are found to be higher when compared with alternative and renewable alcohol fuels. Ethanol has gained in importance in recent years and is one of the more readily used fuels in SI engines in varying percentages with gasoline to reduce the emissions of CO2, a greenhouse gas that contributes to global warming [5]. Use of ethanol-gasoline

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A. K. THAKUR AND A. K. KAVITI

blends reduces CO; in varying the concentration of ethanol, a reduction in CO2 is observed [6]. This review paper aims to study an engine run with varying percentages of gasoline-ethanol blends, gasoline with all other alcohol derivatives, and subsequent alternative fuels, in terms of effects on engine exhaust emissions only. In this review, data from studies conducted to evaluate ethanol-gasoline, ethanol-methanol-gasoline, and methanol-gasoline blends are collected, summarized and compared, to highlight potentials of this blend as an alternative to gasoline fuel.

Reasons for promoting ethanol Ethanol (C2H5OH) is a natural fuel, as it is obtained from renewable energy sources. It is a colorless, transparent, neutral, volatile, flammable, oxygenated liquid hydrocarbon, with a pungent odour and a sharp burning taste [6]. Some fuel properties of ethanol, such as the octane number, heating value, latent heat of vaporization, flame velocity, specific gravity, Reid vapour pressure and distillation curve, are quite different from those of gasoline. Therefore, it becomes crucial to understand the effects of these properties on the performance characteristics of SI engines [7]. An ethanolfuelled engine is less likely to spark off as compared with a gasoline-fuelled engine as the self-ignition temperature of ethanol is higher than that of gasoline at the same compression ratio (CR). This allows for higher detonation-free CR values for SI engines, ensuing higher overall efficiency and shaft power [8,9]. On the other hand, the volumetric efficiency is improved due to higher heat of vaporization, which causes greater cooling of fresh cylinder charge [10]. So ethanol is considered the most suitable fuel and can be readily used in present engines without modifying them [11,12]. Engine power is enhanced abruptly with the usage of ethanol; the reason for this is its octane number, which is very high as compared to gasoline. Fuels with higher octane number can undergo a higher CR before blowing off, thus giving the engine the ability to generate more power. Ethanol, when considered as a fuel for SI engines, has better antiknock characteristics. Ethanol fuel burns more cleanly than regular gasoline does and has high heat of vaporization; therefore, it reduces the peak temperature inside the cylinder and increases the engine power [13–18]. Generally, ethanol or bioethanol is more reactive than gasoline [19]. Ethanol can effortlessly dissolve in non-polar (e.g. gasoline) and polar (e.g. water) substances, as it contains hydroxyl radicals as the polar fraction and carbon chains as the nonpolar fraction as its main constituents [20]. Because of the regenerative and ecological characteristics of ethanol, it is extensively used as an alternative fuel at present. The use of gasoline containing 3–10 vol. % bioethanol has been encouraged in many parts of the

Table 1. Advantages of ethanol fuel over gasoline [23]. Ethanol is a renewable fuel. Ethanol could reduce petroleum imports, improve the balance of payments, improve national energy security, and reduce the reliance on petroleum from unstable areas of the world. Bioethanol if cheaply produced can reduce demands for fossil fuels and the growth in fossil fuel prices. Bioethanol could create stronger demands for feedstocks, thus boosting agricultural prices and producer incomes. Ethanol has a high octane number. Higher latent heat of ethanol increases volumetric efficiency. Ethanol provides more oxygen in the combustion process, which assists in complete burning. Lower vapour pressure of ethanol reduces the evaporative emissions. Ethanol has high laminar flame propagation speed, which makes the combustion process finish earlier and broadens its flammability limit. Ethanol increases thermal efficiency. Ethanol increases engine torque output. Ethanol allows the use of a high compression ratio without knocking. As oxygenated produces cleaner emission. Ethanol is used in direct-injection gasoline engines to avoid knocking. Ethanol burn reduces greenhouse gas emission significantly. Ethanol is easily miscible in gasoline. Ethanol is used widely as an oxygenated portion in gasoline. Ethanol is less toxic than gasoline.

Table 2. Disadvantages of ethanol fuel over gasoline [23]. Energy content of ethanol is lower. Lower vapour pressure of ethanol can contribute to producing unregulated pollutants such as aldehydes. Ethanol use can enhance corrosion of ferrous components such as fuel tanks. Ethanol is a triatomic molecule that results in higher gas heat capacity and lower combustion gas temperature. Low vapour pressure of ethanol makes starting a cold engine difficult.

world for the last few years [21,22]. Tables 1 and 2 shows the merits and demerits of using ethanol compared with gasoline [23].

Comparison of physiochemical properties The quality of fuel to be used in the engine is determined by its physical and chemical properties. Engine combustion quality, performance and emission characteristics differ significantly if the quality of fuel deteriorates. Table 3 shows a comparison of gasoline and ethanol as a fuel when related to combustion. The comparative features of ethanol and gasoline are listed below [23]. 1. Owing to gasoline's higher heating value of approximately one third that of ethanol, a greater amount of fuel is required for ethanol to achieve same engine power output. 2. As ethanol contains 34.7 wt% of oxygen, the combustion temperature is augmented which helps in achieving higher combustion efficiency. 3. The high heat of vaporization of ethanol leads to an increase in volumetric efficiency of the engine. 4. The adiabatic flame temperature is reduced because of the lower C/H atom ratio of ethanol. 5. Ethanol has higher octane number than gasoline, thus halting the phenomenon of premature

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Table 3. Comparison of gasoline and ethanol fuel properties [23]. Property Chemical formula Molecular weight C fraction O fraction H fraction H/C O/C Specific gravity Density (at 15 C) Stoichiometric air-fuel ratio Kinematic viscosity Reid vapor pressure at 37.8 C Research octane number Motor octane number Cetane number Enthalpy of formation (a) Liquid (b) Gas Higher heating value Lower heating value (LHV) LHV at stoichiometric mixture Latent of vaporization Specific heat (a) Liquid (b) Gas Freezing point Boiling point Flash point Auto ignition temperature Vapor flammability limits Laminar flame speed at 100 kPa, 325 K Distillation (a) Initial boiling point (b) 10 (c) 50 (d) 90 (e) End boiling point Water solubility Aromatics volume Vapor toxicity Smoke character Conductivity Color

Unit kg kmol¡1 mass % mass % mass % atom ratio atom ratio kg m¡3 mm2s-1 kPa -

Gasoline C5–C12 114.15 87.4 0 12.6 1.795 0 0.7–0.78 750–765 14.2–15.1 0.5–0.6 53–60 91-100 82-92 8

Ethanol C2H5OH 46.07 52.2 34.7 13.0 3 0.5 0.794 785-809.9 8.97 1.2-1.5 17 108.61–110 92 5–20

kJ mol¡1 kJ mol¡1 MJ kg¡1 MJ kg¡1 MJ kg¡1 kJ kg¡1

¡259.28 ¡277 47.3 44.0 2.77 380–400

¡224.1 ¡234.6 29.7 26.9 2.70 900–920

kJkg-1K-1 kJkg-1K-1 C C C C vol. % cms

2.4 2.5 ¡40 27–225 ¡45 to ¡13 257 0.6–8 ¡33

1.7 1.93 ¡114 78 12–20 425 3.5–15 ¡39

% % % % % % % -

45 54 96 168 207 0 27.6 Moderate irritant Black None Colorless to light amber glass

78 78 78 79 79 100 0 Toxic in large doses Slight to none Yes Colorless

fuel ignition. The fuel can withstand more compression before detonating due to the higher octane number. 6. Thermal efficiency of the engine improves with the usage of ethanol as it possesses a higher laminar flame propagation speed than gasoline, thus finishing the combustion process earlier. 7. Using ethanol with gasoline can benefit petroleum refineries economically, as low-grade gasoline with a lower octane number can be produced. One of the major shortcomings of using ethanol is its high Reid vapour pressure (RVP), which is a measure of a gasoline's volatility. The RVP effect of ethanol on gasoline blends is not linear; ethanol blending at a 5– 6 vol. % increases the RVP by about 8.9631 kPa, but additional ethanol blending does not further increase the RVP. Higher evaporative emissions can be expected with gasoline having an RVP that is unconfined during refuelling and when the car is not operating [14,18,24].

Emission parameters CO emissions When ethanol (containing oxygen) is blended with gasoline, the engine combustion becomes more efficient and therefore CO emission is reduced. The intensification of CO is decreased as the volume percentage of ethanol fuel is increased in the fuel mixture. This is due to the reduction in carbon atom concentration in the blended fuel, and the high molecular diffusivity and high flammability limits which improve the mixing process and hence combustion efficiency.

CO2 emissions The coalescing of CO2 is increased as the volume percentage of ethanol fuel is increased in the fuel mixture. Carbon dioxide is one of the main greenhouse gases. It is observed from the literature that the percentage of CO2 emissions is almost the same in fossil fuels and in alternative fuels. But in the long run the percentage of

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CO2 emissions from alternative fuels are less because of indirect land-use changes.

HC emissions A rich air-fuel ratio (A/F) devoid of oxygen prompts the incomplete combustion of fuel as a misfire produces unburnt HC. When ethanol is supplemented to the blended fuel, it can accommodate more oxygen for the combustion process and leads to the so-called ‘leaning effect’. This indicates that the engine tends to operate in leaner conditions, closer to stoichiometric burning, as the ethanol content is increased. The final result is that better combustion can be achieved; therefore, the HC emissions decrease as the ethanol content increases.

NOx emissions When ethanol containing oxygen is mixed with gasoline, the combustion of the engine becomes better and, therefore, NOx emission is reduced. The concentration of NOx is decreased as the volume percentage of ethanol fuel is increased in the fuel mixture. When the engine condition goes leaner, the combustion process is more complete, and the concentration of NOx emission is reduced.

Progresses in emissions Al-Hasan [25] prepared 10 test blends ranging from 0 to 25% ethanol in increments of 2.5% with unleaded gasoline to study the effect on SI engine exhaust emissions. Tests were carried out at 3/4 throttle opening position and variable engine speed ranging from 1000 to 4000 rpm. Figures 1–3 demonstrate the effect of the ethanol percentage in the fuel blend on regulated emissions. As the ethanol percentage increases to

Figure 1. Variation of CO2 emission versus engine speed [25].


20%, the CO and HC emissions decrease by 46.5% and 24.3%, respectively, of the mean average values when measured at all engine speeds. On the other hand, due to the oxygen content in ethanol the fuel combustion process was enhanced which resulted in an increase in CO2 emissions by about 7.5%. Thus, 20 vol. % ethanol in the fuel blend gave the best results for all emissions at all engine speeds. Ceviz et al. [26] investigated the effects of using ethanol-unleaded gasoline (E0, E5, E10, E15 and E20) blends on cyclic variability (slow burns and incomplete burns) and emissions in an SI engine. Deductions from these figures indicated that as the ratio of the ethanol to unleaded gasoline in the blend was increased to 10%, the HC and CO emissions decreased by 20.2% and 30.01%, respectively, while the CO2 emissions increased. When the ethanol ratio exceeded the 10% level, HC and CO emissions increased and CO2 emissions decreased, due to the increase in the


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temperature of the intake manifold and the decrease in the volumetric efficiency. CO and HC emissions were lower in experiments with pure gasoline than for E15 and E20 blends. However, no problem existed when the engine was operated at an ethanol ratio of 20 vol. %. Varde et al. [27] conducted experiments to evaluate the exhaust emissions characteristics of ethanol-gasoline blends (E10, E22, E85) in a two-valve automotive SI engine. The NOx levels for blends containing 10 or 22% ethanol show a close resemblance to the emission levels of gasoline. However, significant differences in NOx levels can be observed when the engine is fuelled with E85. E85 has high variation in HC emissions, particularly at lighter loads. E10 and E22 did not show much variation in HC emissions. It was also observed that E85 showed reduced HC levels in the exhaust if the engine was operated at a stoichiometric air/fuel ratio. Celik [28] studied the effect of ethanol on engineout emissions. Investigations were carried out in two stages; initially the engine was tested at the original CR of 6:1 and at 2000 rpm engine speed at full throttle; then CR was raised from 6:1 to 8:1 and 10:1 at full load while varying the engine speed in the range of 1500– 4000 rpm at intervals of 500 rpm. The test fuels used were E0, E25, E50, E75 and E100. The values of CO emissions as observed were 3.76%, 2.65%, 2.06%, 1.24% and 0.73% for E0, E25, E50, E75 and E100 fuels, respectively. Increasing the ethanol content reduced the CO2 emissions to 13.25%, 12.14%, 11.62%, 10.25% and 9.51% with E0, E25, E50, E75 and E100 fuels, respectively. HC emissions decreased to some extent as the amount of ethanol added to gasoline increased. The value of HC declined from 331 ppm with E0 to 271 and 245 ppm with E25 and E50, respectively. On the other hand, when running the engine with E75 and E100 there was a significant increase in HC emissions. The value of HC rises to 340 and 483 ppm with E75 and E100 fuels, respectively. The value of NOx declined to 1711, 1434, 1150 and 988 ppm with E25, E50, E75 and E100 fuels,

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respectively, from 2152 ppm with E0 fuel. These observations led to the conclusion that E50 was the most suitable fuel in terms of HC emission. E100 fuel produced lower CO, CO2 and NOx emissions but HC emission increased. E50 had the lowest HC emissions as observed in the first stage of study. In the second stage, CO emission from E50 fuel at a CR of 6:1 was about 45% lower than that with E0 fuel, and at a CR of 10:1 it was 13% lower when compared to running with E50 fuel at a CR of 6:1. CO emission obtained with E50 fuel at a CR of 10:1 is about 53% lower than that with E0 fuel at a CR ratio of 6:1. CO2 emission obtained with E50 fuel at a CR of 10:1 is about 10% lower than that with E0 fuel at a CR of 6:1. CO and CO2 have an inverse correlation; that is, with increasing CO emission the amount of CO2 decreases. HC emission obtained with E50 is about 26% lower than that with E0 fuel at the same CR (6:1). For E50 fuel, HC emission increases by about 19% with an increase in the CR from 6:1 to 10:1. As the CR increases, the combustion chamber surface/volume ratio also increases, and this in turn increases HC. When running with E50 at high CR (10:1), HC decreases by about 12% compared to running with E0 at a CR of 6:1. NOx emission obtained with E50 fuel at the same CR (6:1) is about 33% lower than that with E0 fuel. For E50 fuel, NOx increases by about 22% with an increase in CR from 6:1 to 10:1. As the CR increases, the combustion temperature also increases, and this in turn increases NOx. When running with E50 at high CR (10:1), NOx decreases by 19% compared to running with E0 fuel at a CR of 6:1. Koc et al. [2] studied the effects of unleaded gasoline (E0) and unleaded gasoline-ethanol blends (E50 and E85) on pollutant emissions in a single cylinder four-stroke SI engine at two CR values (10:1 and 11:1). The engine speed was changed from 1500 to 5000 rpm at wide open throttle (WOT). Figure 4 depicts the effect of E0, E50 and E85 addition on CO emissions. Engine operation at a CR of 10:1 resulted in 1% lower CO emission by volume compared to the original value

Figure 4. Variation of CO emissions versus engine speed at CR 10:1 and 11:1 [2].

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Figure 5. Variation of HC emissions versus engine speed at CR 10:1 and 11:1 [2].

for all three fuels (E0, E50 and E85) at all speeds. The lower CO emission can be accounted for by incomplete combustion due to an insufficient amount of air in the air-fuel mixture or insufficient time in the cycle for completion of combustion. Figure 5 displays the variation of HC emissions with respect to varying engine speed at CRs of 10:1 and 11:1. Due to the leaning effect and oxygen enrichment caused by ethanol addition, a significant reduction in HC emissions is observed between speeds of 1500 and 5000 rpm at both CRs. E50 and E85 showed a large reduction in HC emissions as compared to E0. The lowest HC emission was obtained with E85 fuel operation while the maximum HC emission was with E0. The NOx emissions are shown in Figure 6. Compared with E0 the NOx emissions of the blended fuels (E50 and E85) were lower at both CRs. Engine operation at a CR of 11:1 saw slightly higher NOx emissions than that at 10:1 at all speeds. Thus, the conclusion was drawn that operating the engine further on higher CR will result in greater NOx emission levels. Cooney et al. [29] investigated the regulated engine-out emissions of ethanol and butanol blended fuels with gasoline. The test fuels used to carry out the research work were ethanol and two butanol isomers,

1-butanol and iso-butanol, at increments of 10, 20, 50 and 85% by volume. The emissions with all these test fuels were compared with those of gasoline. As the engine load increased, total hydrocarbon (THC) emissions decreased for gasoline and all alcohol blends. In contrast, the ethanol blend showed a significant reduction in THC emissions as compared to gasoline. Iso-butanol as well as 1-butanol showed a slight THC emission increase in particular at low engine loads. As for the final conclusions, increasing the alcohol content did not give significant results in terms of an increase in THC. The results for CO emissions for gasoline and the butanol blends were found to be similar at all load points except the 8.6 bar case. CO emissions were reduced when using high-level blends of ethanol, and remained almost unchanged when using the two tested isomers of butanol. NOx emissions are directly correlated to peak in-cylinder temperatures and are largely affected by the amount of exhaust gas recirculation (EGR). At low engine loads of up to 4.3 bar the EGR valve lift is very similar for all fuels, and the resulting NOx emissions are in the same range. In this load range and at constant EGR settings the absolute levels of NOx emissions are slightly higher for 1-butanol compared to gasoline as well as iso-butanol and ethanol.

Figure 6. Variation of NOx emissions versus engine speed at CR 10:1 and 11:1 [2].

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Kiani et al. [30] carried out investigations with artificial neural network (ANN) modelling of an SI engine to predict the exhaust emissions (CO, CO2, NOx and HC) of the engine. To acquire data for training and testing of the proposed ANN, a four-cylinder, four-stroke test engine was fuelled with ethanol-gasoline blended fuels with various percentages of ethanol (0, 5, 10, 15 and 20%), and operated at different engine speeds, constant engine loads of 25, 50, 70%, and full load conditions. An ANN model based on a standard backpropagation algorithm for the engine was developed using some of the experimental data for training. The performance of the ANN was validated by comparing the prediction data set with the experimental results. The experimental results confirmed that by adding more ethanol, CO was decreased. The oxygen enrichment generated from ethanol increased the oxygen

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ratio in the charge and led to lean combustion. CO2 emission varies with the A/F ratio and CO concentration. As a result, the CO2 emission increased because of the improved combustion. Unburned HC is a product of incomplete combustion which is related to A/F ratio. It is noted that adding ethanol to the blends reduces the HC emission because of oxygen enhancement. When the combustion process is closer to stoichiometric, flame temperature increases, and therefore the NOx emission increases. Results showed that the ANN provided the best accuracy in modelling the emission indices with correlation coefficients equal to 0.98, 0.96, 0.90 and 0.71 for CO, CO2, HC and NOx, respectively, as shown in Figure 7. Costa et al. [31] carried out a comparison of engineout emissions using hydrous ethanol (6.8% water

Figure 7. Predicted emissions versus measured emissions (a) predicted CO versus measured CO (b) predicted CO2 versus measured CO2 (c) predicted HC versus measured HC (d) predicted NOx versus measured NOx [30].

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content in ethanol) or a 78% gasoline–22% ethanol blend on a production 1.0-L, eight-valve, four-stroke engine. Throughout the whole speed range, hydrous ethanol produced higher carbon dioxide and lower carbon monoxide engine-out emissions than the gasoline-ethanol blend. The investigation showed that use of hydrous ethanol is helpful with respect to emissions control. Another benefit of using hydrous ethanol as a fuel is that the HC emissions were also reduced. However, hydrous ethanol yielded higher NOx emissions when a comparison was made with gasoline-ethanol blended fuels for most of the speed range. NOx emission is favored by higher peak chamber temperature, which indirectly is set up by the faster flame speed of hydrous ethanol together with advanced ignition timing. Thus, the NOx emissions were boosted when operating with hydrous ethanol. Gupta et al. [32] investigated the effects of water blended with ethanol on emissions of a 125-cc SI engine at constant engine speed. Four fuels were considered for the analysis: gasohol octane 91 (E10), pure ethanol (E100), ethanol with 10% water by volume (Eh90) and ethanol with 20% water content (Eh80). Tests revealed that when E100 was used as the fuel, CO emissions declined by 76.24%, 46.09% and 56.20% for 25%, 50% and 100% load, respectively, as compared to gasohol (E10). On the other hand, as indicated in Figure 8, water content in ethanol increased the CO



emissions as compared with pure ethanol values. The CO emission observed in the case of Eh 80 is 2.06%, 36.78% and 30.81% higher than that of E100 for 25%, 50% and 100% throttle opening, respectively. Conversely, NOx emissions decreased linearly with water addition. NOx emission in the case of Eh80 is 79.18%, 65.25%, 49.04% lower than with gasohol for 25%, 50% and 100% load conditions, respectively. Figure 9 indicates the linear slowdown in NOx. Hydrous ethanol seems to be a better alternative as shown by Figure 10 in terms of THC (Total hydrocarbons) emissions. Using pure ethanol (E100), a decrement of 56.75%, 50.24% and 58.87% in THC emissions is observed compared to gasohol values for 25%, 50% and 100% load conditions, respectively. Eh80 produces higher hydrocarbons than pure ethanol for all loads. Park et al. [6] investigated the influence of E85 fuel on SI engine emissions, keeping gasoline as a reference fuel. Also, to carry out the investigation on hydrogenenriched gaseous fuel made from ethanol, simulated reformate gas (SRG) supplied by a series of compressed SRG tanks was used in this test. The SRG had the following composition: 18% H2, 15% CO, 12% CO2, and 55% N2. Introducing E85 fuel reduced HC emissions. At 1500 rpm and a fixed excess air ratio the concentration of unburned hydrocarbon was reported to be higher compared to when the engine was run at 2000 rpm.

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The introduction of hydrogen-enriched gas also saw a decrease in HC emissions due to the reduction of carbon in the fuel. A drastic increase in HC emissions was noted when the condition was lean, the reason being the large quenching zone and partial burning. The pinnacle of NOx production was around k = 1.1 for all fuels used. Using E85 as a fuel decreased NOx emissions, and the addition of hydrogen increased the NOx emissions due to its higher flame temperatures. However, using hydrogen-enriched gas the NOx emissions decreased, even at stoichiometric combustion conditions, as hydrogen-enriched gas causes cooling and a charge dilution effect. Adding ethanol decreased CO2 emissions. When the hydrogen-enriched gas was added, the concentration of CO2 emissions decreased due to a reduction in fuel carbon. But as hydrogen-enriched gas contains CO2, the concentration of CO2 emissions increased at stoichiometric conditions (k = 1–1.1). As compared to lean operating conditions (1.2 < k < 1.3), CO2 concentrations were lower than those of base gasoline. For ultra-lean conditions (k > 1.3), CO2 emissions increased with E85 and SRG (hydrogen enriched gas). Parag et al. [5] found that unburnt hydrocarbons, carbon monoxide and carbon dioxide were the prime emissions when ethanol-blended fossil fuels and ethanol-blended fossil fuel flames were used. A typical portable digital exhaust gas analyzer probe was placed in and around the flame with the help of a multi-direction traversing mechanism to measure these emissions. Emission characteristics of ethanol-water blends were also investigated as ethanol readily mixes with water. For ethanol-diesel blended fuels unburnt HC emissions were maximum, while the minimum was observed for ethanol-water blends. Among the ethanol-blended fossil fuels, unburnt HC emissions for ethanol-kerosene blends were minimum. The CO2 emissions were maximum for ethanol-diesel flames. The CO2 emissions were almost equal for ethanol-gasoline and ethanolkerosene flames. The CO emissions were maximum for ethanol-gasoline flames and the minimum for ethanoldiesel flames. An optimum blend of around 70%

ethanol and 30% gasoline, which produced low CO and moderate CO2 and HC emissions, was observed. Schifter et al. [33] investigated the effect of using gasoline-ethanol mid-level blends (0–20% ethanol; E6, E10, E15, E20) on exhaust emissions of a single-cylinder AVL model 5401engine, spark ignited and electronically controlled with DOHC(Dual overhead camshaft). Engine tests were conducted for different lambda values and exhaust emissions were analyzed for carbon monoxide, unburned hydrocarbons and nitrogen oxides. As depicted in Figure 11, the highest calculated reduction in emissions was 52% and 19% for CO and HC, respectively, with a corresponding increase of 60% in NOx emissions for the 20% ethanol fuel with respect to the reference fuel. For the interval of lambda values considered (0.9 < k 6 1.1), 20% ethanol fuel showed an average reduction of 13.6% in CO contents, while an increase in hydrocarbons and nitrogen oxides of around 5% was observed. The fuel with 15% ethanol shows the same trend, with reductions of 7.4% in CO. Fuels with 10% ethanol content or less showed almost no change in emissions. Chen et al. [34] carried out research on the effects of ethanol-gasoline blends on the cold start emissions of an SI engine. The fuels used during the test procedure

Figure 11. Variation of CO, hydrocarbon (HC) and NOx emissions at constant mass fuel rate [33].

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were E0, E5, E10, E20, E30 and E40. The maximum observed values of emissions and rpm were noted during the first 15 s as ECU (Engine control unit) created very fuel-rich conditions in the engine to ensure ignition. ECU reduced the excess fuel injected, as the cooling water temperature increased gradually. As a result, CO and HC emissions gradually decreased, while NO gradually increased; they all reached a stable value around 120 s. At an engine speed of 1000 rpm, no difficulty in cold starting of engine was observed. After 120 s of operation the CO emissions decreased from 3% to 2% and NOx emissions were reduced from 90 to 70 ppm. In addition, only a slight reduction in HC emissions was observed. HC and CO emissions for E40 fuel were reduced to around 400 ppm and 1%, respectively. However, in this case the engine speed was no longer stable. E5 and E10 performed roughly the same as E0, while E20–E40 clearly showed a decrease in HC, CO and NOx emissions. At 120 s, E30 showed 50%, 20% and 10% reduction in CO, HC and NOx emissions, respectively, as compared to E0. It was finally concluded that E40 was not the best-suited fuel for cold starting; the best fuel for cold start emissions was one with an ethanol content of at least 20% but not more than 30%. Karavalakis et al. [4] carried out their investigation on a fleet of gasoline-powered light-duty vehicles ranging in model year from 1984 to 2007, and one flexible fuel vehicle (FFV) to analyze the regulated and unregulated emissions of all the vehicles using various ethanol blends. CARB (california air resources board) phase 2 certification fuels with 11% MTBE (Methyl tert-butyl ether) content, CARB phase 3 certification fuels with 5.7% ethanol content, and E10, E20, E50, and E85 fuels were used during the investigation process. Results indicated that the THC and non-methane hydrocarbon (NMHC) emissions, which are rightly referred to as critical emissions, were lower with the ethanol blends. The only exception was in the case of E85 used in the FFV, which resulted in an increase in THC and NMHC emissions. Older model vehicles displayed drastically lower CO emissions as compared to all vehicles which showed lower CO emissions when ethanol blends were used. Earlier models vehicles showed an increase in NOx emissions as ethanol content was increased, compared with other vehicles, which showed either no decrease or a slight but not significant decrease in NOx emissions. Acetaldehyde emissions were found to be higher side when ethanol percentages were increased. Higher formaldehyde and acetaldehyde emissions were found for E85 compared to CARB phase 2 and 3 and other ethanol fuels. Carbonyl emissions were found to be lower for ethanol blends than those for CARB phase 2 and 3, the only exception being for E85 which was higher.

Zhai et al. [35] investigated the tailpipe emissions of an FFV using E85 as the fuel in comparison with gasoline. Replacing gasoline with E85 reduces CO emissions, may moderately decrease NOx tailpipe emissions, and may increase HC tailpipe emissions. The tailpipe emissions were found to change with varying model year and engine size when comparison was carried out between E85 and gasoline. NOx and HC emissions increased by 82 and 18%, respectively, based on the fuel life cycle. A decrease of 18% was observed for CO emissions. The total GHG emissions are estimated to decrease by 15%, because some of the decrease in fossil CO2 emissions is offset by increases in methane and nitrous oxide emissions. Although life-cycle CO2 and CO emissions decrease for E85 versus gasoline, increases in NOx and HC emissions from substituting gasoline with E85 may aggravate air quality because they are precursors to ozone. Thus, there was a tradeoff between air quality and GHG emissions reduction benefits. Schifter et al. [36] used hydrous ethanol in the volume of HE10, HE20, HE30, HE40, and traditional anhydrous ethanol (E10, E20, E30, E40), and a comparison was carried out to reveal the exhaust emissions of a single-cylinder engine with varying values of air/fuel mixture equivalence ratio. As compared to base fuel (which was formulated by blending five refinery streams employed in commercial gasoline preparation) the tested fuels showed a marginal reduction in emissions. Only the NOx and unburned hydrocarbons presented a significant decrease. Gasoline blended with hydrated ethanol showed better results as compared with gasoline blended with anhydrous ethanol, the reason for this being the water content in hydrated ethanol decreases the temperature, combustion speed and peak pressure thereby improving the NOx emissions, especially for 30% and 40% ethanol content. Figure 12 shows that the maximum NOx emission for anhydrous and hydrated ethanol blends was for lambda values of 1.05 § .01 (between 4% and 6%

Figure 12. Maximum NOx emissions for anhydrous and hydrated ethanol blends [36].

BIOFUELS

lean). For hydrated ethanol, the peak emission decreases as the oxygenated contents increase; nevertheless, for the anhydrous ethanol the NOx increased again when the ethanol contents were 30% or higher. Canakci et al. [37] investigated the exhaust emissions of an SI engine fuelled with ethanol-gasoline (E5, E10) and methanol-gasoline (M5, M10) fuel blends, compared to those of pure gasoline, at two different vehicle speeds (80 and 100 km/h) and four different wheel powers (5, 10, 15, and 20 kW). At the 80 km/h vehicle speed, the decrease in CO emission for E5, E10, M5 and M10 were 18%, 17%, 14% and 11%, respectively, on average as compared to pure gasoline. On the other hand, CO emission increased with an increase in wheel power at 80 km/h vehicle speed, while CO emission of E5 and M10 increased at 5, 10 and 15 kW wheel powers and 100 km/h vehicle speed, and decreased at 20 kW wheel power, compared with the values for pure gasoline. A decrease was observed in CO emission for M5 and E10 at 100 km/h vehicle speed and all wheel powers. On average, the decreases in CO emission for E10 and M5 were 3% and 6%, respectively, compared to pure gasoline. It was also calculated that the increase in CO emission for M10 was 3%, on average, compared to pure gasoline. The decreases in CO2 emission for E5, E10, M5 and M10 were 9.5%, 8%, 11.3% and 3%, respectively, on average, compared to pure gasoline. CO2 emissions of E5, E10 and M5 are lower than those of gasoline at all wheel powers. When M10 was used, an increase occurred in CO2 emission at 15 and 20 kW wheel powers at the speed of 100 km/h. When the average values were taken into consideration, the CO2 emission of M10 increased only 0.3% compared with gasoline, while CO2 emissions of E5, E10 and M5 decreased by 4%, 3.7% and 7%, respectively, at a vehicle speed of 100 km/h. The average decreases in unburned HC emissions of E5, E10, M5 and M10, compared to pure gasoline, were 27%, 32%, 35% and 30%, respectively, at 80 km/h vehicle speed. Unburned HC emissions decreased linearly as the wheel power increased for the E5, E10 and M5 fuels at 100 km/h vehicle speed. The decreases in HC emissions of E5, E10, M5 and M10 were 12%, 16%, 10% and 17%, respectively, on average, compared to pure gasoline. The average decrease in NOx emissions of E5, E10, M5 and M10 compared to pure gasoline was 11%, 15.5%, 9% and 1.3%, respectively, at 80 km/h vehicle speed. At 100 km/h, NOx emissions of E5, E10 and M5 decreased by 10.5%, 13.5%, and 5%, respectively, while the NOx emission of M10 increased by 2.8%, on average, compared with values for pure gasoline. Costagliola et al. [38] carried out an experimental study on a conventional 1.6-L port-injection engine with some bioethanol/gasoline blends (0, 10, 20, 30, and 85 vol. % of ethanol in gasoline) and with a 10 vol. % blend of n-butanol in gasoline, to investigate the

11

Figure 13. Variation of CO emission versus engine speed [39].

engine-out emissions. THC concentration increased for all ethanol and butanol blends; however, for the highest alcohol content a small decrease in THC was observed. CO emissions decreased with an increase in the alcohol content in the blend. The strongest reduction was 15% as observed for E85. NOx emissions produced similar results to THC, reaching the maximum value between gasoline and E85 (almost 4%). Altun et al. [39] investigated the effect of E0, E5, E10, M5, M10 on the exhaust emissions of an SI engine at variable engine speeds from 1000 and 4000 rpm, with a 500-rpm period and at 3/4 throttle opening position. A reduction in CO was observed when using blended fuels as compared with unleaded gasoline, as depicted in Figure 13. Using E5 and E10, the relative decrease in the CO emissions was found to be 7% and 9.8%, respectively. On the other hand, the decrease in CO emissions as observed with M5 and M10 was 9% and 10.6%, respectively. A comparison of CO2 emissions for all test fuels us illustrated in Figure 14. The highest CO2 emissions were obtained with M10, followed by E10. A comparison of HC emissions for all test fuels is depicted in Figure 15. As observed, HC emissions of M5 and M10 decreased by 6.7% and 13%; while using


12


Figure 15. Variation of hydrocarbon (HC) emission versus engine speed [39].

E5 and E10 the HC emissions dropped by 5.3% and 15% when compared with E0. Curtis et al. [40] carried out experiments on an engine using pure gasoline (E0), 10% ethanol (E10) and 20% ethanol (E20) blends. E20 displayed lower NOx emissions than pure gasoline. The 10% ethanol blend produced the highest NOx emissions at the two lower fuel flow rates. A similar order of NOx emissions was observed for all three fuels, signifying that all the emissions were less than 50 ppm. CO emissions for gasoline (E0) were higher compared with both ethanol blends (E10 and E20). The 20% ethanol blend (E20) produced the highest CO2 emissions. The 10% ethanol blend produced the lowest CO2 emissions and was found to be similar to gasoline. All of the results were within 0.5% of each other. Gravalos et al. [41] carried out an experimental study comparing the effects of using lower and higher alcohol-gasoline blends on regulated emissions emitted by a small non-road SI engine. Altogether, 21 test fuels comprising lower and higher molecular mass were prepared with gasoline as the base fuel, and investigations were carried out. The eight lower molecular mass fuels were gasoline-methanol and ethanol blends containing 5% (M5, E5), 10% (M10, E10), 20% (M20, E20) and 40% (M40, E40) alcohol. The 12 higher molecular mass alcohols blended with gasoline were propanol, butanol and pentanol blends containing 5% (PR5, BU5 and PE5), 10% (PR10, BU10 and PE10), 20% (PR20, BU20 and PE20) and 40% (PR40, BU40 and PE40) alcohol. Compared to the emissions of the other test fuels, CO emissions for M40 were lower (4.25– 5.24% vol). CO emissions for test fuel PE5 were the highest of all (13.55–13.78% vol.). E40, PR40, BU40 and PE40 showed the same emission trend (6.19–9.54% vol.), which was obviously higher than in the case of M40. As expected, CO emissions increased (12.10–13.01% vol.) for gasoline and other low-alcohol-concentration test fuels (M5, E5, PR5 and BU5). Wrapping up the experimental

investigation, it was found that when the concentration of high or low molecular mass alcohol in the fuel blend was increased, lower CO emissions were observed, due to the oxidized nature of alcohols. Concerning CO2 emissions, these increased gradually as the total percentage of alcohol in the blend increased. CO2 emissions ranged from about 7.33 to 13.27% vol. At an engine load of 25% the highest CO2 value was emitted for ME40, and the lowest CO2 emissions were observed for PE5. HC emissions gradually decreased with increasing alcohol percentage in the blend. Moreover, HC emissions gradually decreased when moving from high to low engine load operation. HC emissions ranged from 536 to 1796 ppm for all alcohol-gasoline test fuels. The highest engine HC emissions were observed for the ET5 fuel at full engine load (100%). HC emissions were lower for the ME40 test fuel at an engine load of 25%. Remarkably, the ME40 fuel's emissions were extremely high. ME40 emissions observed were 5–8 times higher than ME5 emissions at different engine loads. NOx emissions ranged from 32 to 839 ppm for alcohol-gasoline test fuels. The highest engine NOx emission was observed for the ME40 fuel at an engine load of 25%, and NOx emission was lower for the PE5 test fuel at an engine load of 75%. Moreover, NOx emissions changed depending on the operating conditions of engine. Masum et al. [42] focussed their research work on analyzing emissions characteristics using methanol, ethanol, propanol and butanol in a four-cylinder gasoline engine. The engine was fuelled with 20% methanol-80% gasoline (M20), 20% ethanol-80% gasoline (E20), 20% propanol-80% gasoline (P20) and 20% butanol-80% gasoline (B20) at varying engine speeds. Figure 16 depicts the variation in CO exhaust emissions in relation to engine speed. In M20, E20, P20 and B20, CO emissions were significantly lower than those of gasoline, by (on average) 16.6%, 13.9%, 9.6%, and 5.6%, respectively. Thus, alcohol-gasoline blended fuel emitted less CO than gasoline fuel did. Figure 17 shows the emissions of unburned HC by all test fuels at speeds ranging from 1000 to 6000 rpm. These emissions were slightly lower in all alcohol-gasoline blends

Figure 16. Variation of CO emission versus engine speed [42].

BIOFUELS

Figure 17. Variation of hydrocarbon (HC) emission versus engine speed [42].


than in pure gasoline. On average, emissions of unburned HC by M20, E20, P20 and B20 significantly decreased by 10.7%, 14.9%, 5.4%, and 2.9%, respectively. HC emission decreased more at high engine speeds than at low speeds. Figure 18 presents the variation in CO2 emission across different fuels. As per the study results, CO2 emission was higher in alcohol-gasoline blends than in pure gasoline; on average, CO2 emissions were 15%, 12%, 6.5% and 5.8% significantly higher for M20, E20, P20 and B20, respectively. Figure 19 depicts the variation in NOx emission at WOT and at different engine speeds. On average, NOx emissions by M20, E20, P20 and B20 were significantly higher than those from pure gasoline by 20%, 32%, 14.5% and 11%, respectively. Sayin et al. [43] examined the engine-out emissions of an SI engine with varying CRs. The test fuels used for their research work were pure ethanol, methanol and

Figure 19. Variation of NOx emission versus engine speed [42].

13

unleaded gasoline. These tests were conducted on four different CRs, 8.0:1, 8.5:1, 9.0:1 and 9.5:1, with a wide-open throttle and original ignition timing, and at 2400 rpm. Figure 20 shows the emissions characteristics for UH (unburned hydrocarbons), CO, NO, and CO2 using unleaded gasoline, ethanol and methanol at different CRs. The UHC emissions decreased when using pure ethanol and methanol instead of unleaded gasoline fuel at all CRs. The minimum UHC emissions noted for unleaded gasoline, ethanol and methanol were 162 ppm, 115 and 97 ppm, respectively, at a CR of 8.5:1. Compared to unleaded gasoline, UHC emissions for ethanol and methanol decreased by about 22.79% and 28.22% on average at all CRs. CO emissions also diminished to about 14.49% and 29.37% for ethanol and methanol fuels. However, the CO2 emission increased by about 1.46% with ethanol and by about 2.19% with methanol at a CR of 9.0:1. Meanwhile, the maximum values of NOx emissions decreased by about 18.1% with ethanol and by about 22.97% with methanol. Siwale et al. [44] compared the effects of dual-alcohol (n-butanol and methanol) and single-alcohol (methanol) blends in gasoline fuel (GF) in terms of emission characteristics of an SI engine. The test fuels were GF and blends M53b17 (53% methanol, 17% nbutanol and 30% GF by volume), M20 and M70. The blend M53b17 was selected to match the vapour pressure (VP) of GF, whereas M70 was chosen to match the total alcohol content in the blend. When the spark timing was set to 27.5 CAD (Crank angle degree) bTDC (Before top dead centre), higher NOx emissions were noted for M53b17 as compared to M70. When measured against high BMEP ( Break mean effective pressure), GF produced higher NOx emissions as compared to M70 and M53b17. The NOx emission for the M20 blend was maximum due to its slower combustion rate. The emissions of CO using GF at partial loads (2.4 and 3.1 bars) increased considerably because of incomplete combustion. The emission concentrations of UHC produced by M53b17 and M70 blends versus ST were identical; however, these emissions were lower than those of M20. The emission of UHC was greatest for GF. Generally, the slightly higher excess ratio at the same high BMEP for M20 than for the other two blends (M53b17 or M70) resulted in lower CO2 emissions produced using M20 than M53b17 or M70 blends. CO2 emission increased using GF at low BMEP. Turkoz et al. [45] investigated the best ignition timings in an SI engine using an E85 ethanol blend by changing the timing angle with respect to gasoline under wide-open throttle conditions; at this throttle position, the engine speeds were varied in the interval of 2000–4000 rpm. CO and CO2 emissions showed a slight dependency on the ignition advance. A very small increase in CO and a small decrease in CO2 emissions were noted. HC emissions increased with

14



advanced spark timings, which was noticed at 3000, 3500 and 4000 rpm engine speeds for 40 advanced ignition. NOx emissions decreased with delayed ignition timings. Overall, the best emissions were obtained with 40. Balki et al. [46] studied the effect of alcohol (ethanol and methanol) use on emissions characteristics of a low-power single-cylinder engine at full throttle and varying engine speeds. The variations in CO and HC emissions obtained from gasoline, ethanol and methanol usage are shown in Figure 21. HC emissions decreased by 13.6% and 27.12% with ethanol and methanol usage as compared with gasoline. CO emissions also decreased, by 29.07% and 31.34%, with ethanol and methanol usage as compared with

gasoline. However, with increased engine speed, CO emission decreased, and HC emission increased after reaching the minimum point. The changes in CO2 and NOx emissions for gasoline, ethanol and methanol usage at the different engine speeds are shown in Figure 22. CO2 emissions increased by 4.4% and 2.51%, respectively, when ethanol and methanol were used as fuel as compared to gasoline, and NOx emissions decreased by 49% and 47.6% when ethanol and methanol were used. Increasing the engine speed for all tested fuels saw a rise in CO2 emissions. Lower amounts of NOx emissions were obtained for the alcohol studies when compared to the gasoline case. The minimum NOx emission was observed to be 682 ppm at 1600 rpm.



BIOFUELS

Elfasakhany [47] investigated the pollutant emissions of an SI engine fuelled with iso-butanol-gasoline blends. Effects of various isobutanol blends mixed with gasoline at 3%, 7% and 10% by volume (iB3, iB7, iB10) on the regulated emissions were studied and a comparison was carried out with pure gasoline. The engine was operated at a speed range of 2600–3400 rpm. Using iso-butanol-gasoline blends, CO2 is decreased by an average of 33% as compared to the pure gasoline. The drop in emissions fluctuates with the engine speed, generating an average drop of 43% and 27% at 2600 and 3400 rpm, respectively, as compared with pure gasoline. . As indicated from the experimental investigation, CO emissions of gasoline were higher than those of the blended fuel at speeds less than or equal to 2900 rpm. Using 10% vol. iso-butanol in gasoline, the level of CO emission was reduced by about 30% as compared to gasoline at 2600 rpm. But when the engine was run at speeds higher than 2900 rpm, the blended fuels produced higher levels of CO emissions as compared to gasoline fuel. At 3400 rpm the CO emissions of blended fuels are higher than those of the neat gasoline by about 2.5%. UHC emissions behaved in the same manner as the CO emissions. The UHC emissions for blended fuels are lower than those for the gasoline at speeds of less than 2900 rpm. Using 10% vol. iso-butanol in gasoline, the level of UHC was reduced by about 21% as compared to gasoline at 2600 rpm. However, when the engine is operated at speeds greater than or equal to 2900 rpm, the UHC emissions of blended fuels are higher than those of the gasoline fuel. At 3400 rpm the UHC emissions of blended fuels are higher than those of the neat gasoline by about 7%. Sayin et al. [48] focused on the effect of three different CRs (9:1, 10:1 and 11:1) at 2600 rpm with a wideopen throttle on the emission characteristics of isobutanol in different volume ratios blended with gasoline: 0% (ISB0), 10% (ISB10), 30% (ISB30) and 50% (ISB50). The CO emissions decreased with an increased CR. ISB30 and ISB50 showed a considerable decrease in CO emissions, with the lowest CO emission obtained from the use of ISB50 fuel at a CR of 11:1. The reduction in CO emission at higher CR was credited to the higher combustion chamber temperature value. The minimum value of CO was found to be 0.81 g/kWh for ISB50 at 11:1 CR. The CO2 emissions showed the opposite behavior when compared to the CO exhaust emissions. Increasing the CR for all the test fuels led to an increase in the CO2 emission. The maximum value of CO2 emission was 26.5 g/kWh at a CR of 11:1, for ISB50. UHC emissions decreased at all CRs as the iso-butanol content of mixture fuel increased. Reductions in UHC emissions were pronounced with an increase in CRs. The use of ISB50 with a CR of 11:1 resulted in the lowest value of (0.36 g/kWh) for UHC emissions. UHC

15

emissions increased at low CRs due to insufficient heat of compression which delayed ignition. Elfasakhany [49] studied exhaust emissions from an SI engine fuelled with ethanol-methanol-gasoline blends, and the effects of using blends with low contents of ethanol-methanol (3–10 vol. %) in gasoline compared to ethanol-gasoline blends, methanol-asoline blends and pure gasoline on emissions characteristics. Experiments carried out at varying engine speeds from 2600 to 3400 rpm resulted in the lowest CO2 emissions and highest CO and UHC emissions for neat gasoline. Methanol-gasoline gave the best emission results, i.e. it displayed lower emissions of CO and UHC and the highest CO2 emissions. As compared to M3, M7 and M10, ethanol-gasoline blends gave higher CO and UHC emissions and lower CO2 emissions. EM fuels showed a moderate level of emissions, between those of ethanol and methanol fuels. A decrease of 15.5%, 31% and 42% in CO emissions was observed with E3, E7 and E10, respectively, when compared with neat gasoline. The CO emissions of M3, M7 and M10 decreased by about 17.7%, 51.5% and 55.5%, respectively; on the other hand, the CO emissions of EM3, EM7 and EM10 decreased by about 17.5%, 35.5% and 46.6%, respectively, as illustrated in Figure 23. The comparison of UHC emissions for test fuels is also shown in Figure 23. Compared to neat gasoline, the UHC emissions of M3, M7 and M10 were reduced by about 19.6%, 16% and 26%, respectively; while those of E3, E7 and E10 were reduced by about 3.5%, 14% and 21.5%, respectively; and those of EM3, EM7 and EM10 were reduced by about 10.7%, 15.3% and 23.2%, respectively. As observed, UHC was very low for the M blends, followed by EM and then by E, compared to the neat gasoline. A comparison of CO2 emissions of the test fuels is shown in Figure 23. CO2 emissions increased while the CO and UHC emissions decreased. CO2 was maximized for M, followed by EM, then E and finally the G fuel. The CO2 emissions of M3, M7 and M10 were higher than those for gasoline fuel by about 3%, 8% and 9.2%, respectively; the CO2 emissions of EM3, EM7 and EM10 were higher by about 3%, 5.1% and 7.1%, respectively; and the CO2 emissions of E3, E7 and E10 were higher by about 1%, 1.7% and 4%, respectively, compared to the neat gasoline. Simeon [50] investigated the effect of ethanol (E0, E5, E10, E20, E30 and E50) and methanol (M0, M5, M10, M20, M30 and M50) fuel blends on SI engine emission characteristics. In this regard, a one-dimensional engine simulation model was developed using the software AVL BOOST to analyze the emissions characteristics at full load conditions for speeds ranging from 1000 to 6500 rpm in steps of 500 rpm. It was observed that CO concentration decreased when blends of higher volumes of ethanol and methanol were used.

16


Figure 23. Variation of CO, UHC and CO2 emission versus engine speed [49].

The lowest CO emissions were obtained with blended fuel containing methanol (M50). It was noted that when the ethanol and methanol percentage increases, the HC concentration decreases. An increase in the relative air-fuel ratio led to a decrease in the concentration of HC emissions. A comparison of the decrease in HC emissions among the blended fuels indicated that methanol was more effective than ethanol. M50 displayed the lowest HC emissions. It was concluded that HC emissions were lower when the complete combustion was greater. Investigations indicated that when the ethanol and methanol percentage increased to 30% E30 (M30), the NOx concentration increased, after which it decreased with an increase in the ethanol (methanol) percentage. Kim et al. [51] examined the effect of ethanol port fuel injection and gasoline direct-injection systems on emission characteristics under full load. The experiment was conducted by varying the ethanol injection timings and at CR 9.5 and 13.3. Figure 24 demonstrates the emission characteristics at CR 9.5. There was no variation in THC emission even though ethanol was added. NOx emission showed a marginal increase of 10% with the addition of ethanol. CO emission decreased with the addition of ethanol. The effect of

the injection timing of ethanol seemed insignificant for THC, NOx and CO emission characteristics. THC and CO emissions decreased by approximately 14.7% and 28.3%, respectively, at a CR of 9.5 when ethanol was injected at 5400 bTDC. As illustrated in Figure 25, when ethanol addition was increased by 4 times at CR 13.3, the augmentation in oxidation of THC and CO was magnified. As the ethanol injection time was retarded from 540 to 3050 bTDC, a slight increase in CO emission was observed. On further retardation of ignition timing to 2700 bTDC, THC and CO emissions increased, and NOx emission decreased. Najafi et al. [52] used response surface methodology (RSM) to optimize the exhaust emissions of an SI engine operated with ethanol-gasoline blends of 5%, 7.5%, 10%, 12.5% and 15% (called E5, E7.5, E10, E12.5 and E15). In the experiments, the engine was run at various speeds for each test fuel, and 45 different conditions were constructed. The concentration of CO and HC in the exhaust pipe was decreased by introducing ethanol blends, but CO2 and NOx emissions increased. The experiments were designed using a statistical tool known as DoE (design of experiments) based on RSM. Engine-operating parameters were optimized



Ceviz et al. (2005)

Varde et al. (2007)

Celik (2008)

Koc et al. (2009)

Cooney et al. (2009)

2.

3.

4.

5.

6.

Sl. no Study 1. M. Al-Hasan (2003)

[29] E0, E5, E10, E15, E20

[2] E0, E50, and E85

[28] E0, E25, E50, E75, E100

[27] E10, E22, E85

[26] E5, E10, E15, E20

Different blend compositions Ref. [25] E0, E40, E60

4-cylinder, 4-stroke SI engine, 86.4 mm bore, 67.4 mm stroke, 1.581 dm3 displacement

4-cylinder, 4- stroke SI engine, 1452 cm3 swept volume

2-valve, 4-cylinder 4-stroke engine, 87.5 mm bore, 104 mm stroke, 2.5 L displacement, 9.4 CR port injected Single-cylinder 4-stroke SI engine, 80.26 mm bore, 88.9 mm stroke, 5:1–13:1 CR, maximum power 15 kW at 5400 rpm

Single-cylinder 4-stroke SI engine, 250 cm3 displacement, 6:1–10:1 CR

Engine specifications Single cylinder, 80.26 mm bore, 88.9 mm stroke, 5:1–13:1 CR

Table 4. Comparison of emission parameters.

–

–

–

9.2:1 CR, 2000 rpm, 62/5800(kW/rpm) maximum power, 13/2900(daNm/rpm) maximum torque, water cooled.

(i) Engine operating on compression ratio of 11:1 saw slightly higher NOx emissions than that at 10:1 at all speed ranges

9:1 CR, 52/5600(kW/rpm) maximum power, 1000–4000 rpm

–

(i) The values of CO emissions as observed were 3.76%, 2.65%, 2.06%, 1.24% and 0.73% for E0, E25, E50, E75 and E100 fuels, respectively

(i) Engine operating at compression ratio of 10:1 resulted in 1% lower CO emission by volumes compared to the original value for all three fuels (E0, E50 and E85) at all speed ranges.

(i) Decreased level of emissions for E22 and E85

(i) The value of NOx declined to 1711 ppm, 1434 ppm, 1150 and 988 ppm with E25, E50, E75 and E100 fuels, respectively, from 2152 ppm with E0 fuel

–

–

–

(i) Increasing the ethanol content reduced the CO2 emissions to 13.25%, 12.14%, 11.62%, 10.25% and 9.51% with E0, E25, E50, E75 and E100 fuels, respectively

(i) As the ratio of the ethanol to ethanol–unleaded gasoline blend was increased to 10%, CO2 emissions increased

Results of research objects (different kinds of emissions) CO2 NOx – (i) CO2 emission increases by about 7.5%

(i) As the ratio of the ethanol to ethanol–unleaded gasoline blend was increased to 10%, CO emissions decreased by 30.01% and CO2 emissions increased

CO (i) As the ethanol percentage increases to 20%, the CO emission decreases by 46.5%

1500–5000 rpm, CR 10:1 and 11:1, IgT: 70 bTDC–20 aTDC

Constant speed, variable torque, fixed throttle opening

Operational conditions 2000, 3500, 5000 rpm, 8:1–13:1 CR petrol injection, IgT: 700 bTDC–200aTDC, max power 15 kW, max speed 5400 rpm 6:1, 8:1 and 10:1 CR, 1500–4000 rpm, transistorized coil ignition system, air and water cooled

(continued)

(i) The value of HC declined from 331 ppm with E0 to 271 and 245 ppm with E25 and E50 fuel respectively (ii) The value of HC rises to 340 and 483 ppm with E75 and E100 fuels, respectively (i) A significant reduction in HC emissions is observed between 1500 and 5000 rpm speeds at both compression ratios (10:1 and 11:1) (ii) E50 and E85 showed significant reduction in HC emissions as compared to E0 – (i) Decrease for E10

(i) As the ratio of the ethanol to ethanol–unleaded gasoline blend was increased to 10%, the HC emissions decreased by 20.2% (i) Decreased level of emissions for E85

HC (i) As the ethanol percentage increases to 20%, the HC emission decreases by 24.3%

BIOFUELS 17

Costa et al. (2010)

Gupta et al. (2010)

Park et al. (2010)

Parag et al. (2011)

Schifter et al. (2011)

8

9

10

11

12

Sl. no Study 7 Kiani et al. (2010)

Table 4. (Continued )

Single cylinder, 4-stroke SI engine, 80.26 mm bore, 88.9 mm stroke, Tappet clearance 0.3– 0.4 mm

4-cylinder, 4-stroke SI engine, 71 mm bore, 83.6 mm stroke, 1323 cc displacement

[33] E0, E3, E7, E10, Single-cylinder, M3, M7, M10, 4-stroke SI engine, EM3, EM7, EM10 65.1 mm bore, 44.4 mm stroke

[5] E0, E10, E20, E40, E60

[6] E5, E7.5, E10, E12.5, E15

Engine specifications Single-cylinder SI engine, 2.5 BHP, 70 mm bore, 66.7 mm stroke, 2.5:1–10:1 CR, 3000 rpm [31] E22, E100 4-cylinder, 8-valve fuel engine, 70.0 mm bore, 64.9 mm stroke, 999.057 cm3 swept volume [32] E0 (E50 + 5, E60 + 3-cylinder, 10*) 4-stroke MPFI engine, 86.5 mm bore, 72 mm stroke, 6 engine valves, 796 cc displacement

Different blend compositions Ref. [30] E0, E10, E15, E25, E35, K15, K25, K35, LPG

–

(continued)

– (i) 4.26% increase for E60 when IgT:10 CA and CR 8:1 (ii) 1.82% increase for E60 when IgT:36 CA and CR 8:1 (iii) Maximum at 0.9 RAFR for all test fuels at CR of 8:1 and 10:1 (i) Highest for M3, M7, M10 (i) Highest for E0, E3, E7, E10; highest for M3, M7, M10 –

(i) Increased —

–

(i) Increased

–

(i) Increases with high CR; E100 produces higher volumetric efficiency at low CR at all speeds as compared with E22

HC (i) Increased for all CR (ii) Highest for LPG

–

(i)Increment of 23.24% for (E60 + 10) at 2800 rpm as compared to E0

(i) Increases with high CR

Results of research objects (different kinds of emissions) NOx CO2 (i) Maximum for E0 & E35 – (ii) Lowest for K35

(i) Higher BTE with E100 as (i) Higher BSFC with E100 as compared with E22 at all engine compared with E22 at all speeds engine speeds

CO –

8.7:1 CR, – 2200, 2400, 2600, 2800, 3000 rpm, 35.0/5000 (bhp/rpm) maximum power, 6.1/3000 (kgm/rpm) maximum torque, water cooled 9.7 CR, (i) Decreased 1500–4000 rpm, 103/2750 (Nm/rpm) maxiumum torque, 47/ 5200 (kW/rpm) maximum power, combustion order 1-3-42 (i) Minimum at 1.05 RAFR and CR 5:1–13:1CR, 11:1 2000 rpm, (ii) For E40 maximum decrement RAFR: 0.8-1.2 of 15% IgT: 700 bTDC–200 aTDC, Overhead cam shaft, two vertical valves, water cooled 7:1 CR, – 2600–3450 rpm, air cooled

10:1–12:1 CR, 1500–6500 rpm, IgT: 150–350 bTDC, 1.11 fuel/air mixture equivalence ratio

Operational conditions 2400 rpm, 4.6:1, 6:1, 8:1 and 9:1 CR, eddy current dynamometer loading, crank start method, air cooled

18 A. K. THAKUR AND A. K. KAVITI

Karavalakis et al. (2012)

Zhai et al. (2012)

Schifter et al. (2013)

Canakci et al. (2013)

14

15

16

17

Sl. no Study 13 Chen et al. (2011)


[37]

[36]

[35]

[4]

Engine specifications 4-cylinder, 4-stroke SI engine, 1581 cc displacement

Operational conditions 9.2:1 CR, 2000–4000 rpm, IgT: 2–6 , 64.1 kW at 5800 rpm, maximum brake power 130 Nm at 2900 rpm, maximum brake torque 105.6 Nm brake torque at 5800 rpm 185 kw maximum power, water cooled 10.4:1 CR, E10, E20, E50, E85 4-cylinder, 5, 10, 15, 20 kw wheel 4-stroke SI engine, power, 16 valve, 80 km/h, 100 km/h vehicle 1396 cm3 cylinder volume speeds, 130/4300 (Nm/rpm) maximum torque, 66/5600 (kW/rpm) maximum power, water cooled E0, E3, E7, E10 Single-cylinder, 1.5 kW output power 4-stroke SI engine, approx. 17 kg weight approx. 0.6 L oil volume, , 515 £ 345 £ 370 mm magnetic ignition voltage, (L £ W £ H), 7:1CR, 65.1 mm bore, air cooled, 44.4 mm stroke, 2600–3500 rpm 79.55 mm connecting rod E0, E5, E10, E15, Single-cylinder, 8:1-9.2:1 CR E20, E25, E30 4-stroke SI engine, 1500 rpm and variable 76.2 mm bore, IgT 110.0 mm stroke, 241.3 mm connecting rod 10: 1 CR, M20, E20, P20, 4-cylinder 1000–6000 rpm, B20 SI engine, 3 1596 cm displacement fuel system multi-point 78 mm bore, electric port fuel system, 84 mm stroke, maximum output 78 kW 131 mm connecting at 6000 rpm, rod length maximum torque 135 Nm at 4000 rpm, maximum power 150 kw 100% load condition

Different blend compositions Ref. [34] E85

(i) Increment of 3.5% at CR of 8:1 for E30

(i) For M20, E20, P20 and B20 BTE was higher than that of gasoline by 3.6%, 2.15%, 0.7% and 1.86%, respectively

(i) For M20, E20, P20, and B20 BSFC was higher than that of unleaded gasoline by 7.58%, 5.17%, 4.43%, and 1.95%, respectively

–

(i) For E5, E10, M5 and M10 increment of 1.9%, 2.5%, 1.8% and 4.7%, respectively at speed of 100 km/h (ii) For E10, M5 and M10 increment of 0.4%, 2.2% and 2.5%, respectively and reduction of 0.8% for E5

–

(i) For M20, E20, P20, and B20, an increase in the torque of gasoline by 5.02%, 3.39%, 10%, and 9.2%, respectively

(i) Increases

–

Results of research objects (different kinds of emissions) NOx CO2 – (i) Increases with IgT:40

(i) Increment of 4.3% at CR of 8:1 for E30

(i) Decreases

(i) For E5, E10, M5 and M10 increment of 2.8%, 3.6%, 0.6% and 3.3%, respectively at speed of 80 km/h (ii) For E5, E10, M5 and M10 increment of 0.2%, 1.5%, 1.1% and 1.2%, respectively at speed of 100 km/h

CO –

–

(continued)

(i) Increment of 4% at CR of 8:1 for E30 —

(i) Increases (ii) Increases

–

HC (i) Increases with IgT:40 (ii) No change with varying IgT (iii) Higher at richer fuel

BIOFUELS 19

[39] E0, E5, E10, E20

Altun et al. (2013)

Masum et al. (2014)

Yousufuddin et al. (2012)

Siwale et al. (2014)

Balki et al. (2014)

19

20

21

22

23

Single-cylinder, 4-stroke SI engine, 196 cc, 8.5 CR air cooled

Engine specifications Single-cylinder, 4-stroke SI engine, 76.2 mm bore, 82.84 mm stroke Single-cylinder, 4-stroke SI engine, 100 cc, 50 mm bore, 50.6 mm stroke 4-cylinder SI engine, 1596 cm3 displacement 78 mm bore, 84 mm stroke, 131 mm connecting rod length

4-cylinders Suzuki RS-416 1.6 L, 78 mm bore, 83 mm stroke, 1.586 L swept volume 11.1 CR [46] Ethanol, methanol Single-cylinder, 4-stroke, 196 cc, air-cooled, low-power gasoline engine (DATSU LT 200) 8.5:1 CR

[44] E0, M53b17, M20, M70

[43] E0, E100, M100

[42] M20, E20, P20, B20

Different blend compositions Ref. [38] E0, E10, E20, E30, E40

Sl. no Study 18 Costagliola et al. (2013)


Power (kW) 92 (@ 6800 rpm) maximum torque (Nm) 148 (@ 4800 rpm) camshaft DOHC with VVT number of valves 4

–

(i) At 6000 rpm using E5, E10, E20 increment by 0.29%, 0.59% and 4.77% as compared to gasoline

Results of research objects (different kinds of emissions) NOx CO2 (i) Increases by more than 6% – with E40 (i) Increases (ii) Increases

HC

(i) CO emissions also decreased by (i) CO2 emissions increased by 29.07% and 31.34% with ethanol 4.4% and 2.51%, respectively when ethanol and methanol and methanol usage as were used as fuel as compared with gasoline compared to gasoline

(i) The emissions of CO using E0 at (i) Lower CO2 emission produced using M20 than partial loads (2.4 and 3.1 bars) M53b17 or M70 blends increased considerably

(i) CO2 emission increased to about 1.46% and 2.19% with E100 and M100 at the CR of 9.0:1

(i) NOx emissions decreased by 49% and 47.6% when ethanol and methanol were used

(continued)

(i) HC emissions decreased by 13.6% and 27.12% with ethanol and methanol usage as compared with gasoline

(i) The maximum values of (i) Reduction of 29.01% NOx emissions decreased to and40.12%, respectively, about 18.1% and 22.97% at a CR of 8.5:1 for E100 with E100 and M100 and M100 (ii) For E100 and M100 emissions decreased to about 22.79% and28.22% on average at all CRs (i) HC emissions were lower (i) Blend M70 produced less than those of M20 NOx emission than M53b17 (ii) NOx emission for M20 blend was maximum

(i) At 6000 rpm using E5, E10, E20 increment by 2.31%, 2.77%, and 4.16% as compared to gasoline — (i) NOx emissions by M20, E20, (i) HC emissions for M20, (i) CO emissions were significantly (i) CO2 emissions were 15%, 12%, 6.5%, and 5.8% P20, and B20 were E20, P20, and B20 lower than those of gasoline by significantly higher for M20, significantly higher than significantly decreased by averages of 16.6%, 13.9%, 9.6%, E20, P20, and B20 respectively that by pure gasoline at 10.7%, 14.9%, 5.4%, and and 5.6%, for M20, E20, P20, and 20%, 32%, 14.5% and 11% 2.9%, respectively B20 respectively respectively

(i) Increases

CO (i) Increases by 20% with E30

10:1 CR, 1000–6000 rpm, fuel system multi-point electric port fuel system, maximum output 78 kW at 6000 rpm, maximum torque 135 Nm at 4000 rpm, maximum power 150 kw 100% load condition (i) CO emissions diminished to 8.0, 8.5, 9.0, 9.5 CR about 14.49% and 29.37% for 2400 rpm, 0 E100 and M100 ignition timing (23 bTDC), constant equivalence ratio (1.0)

4000–8000 rpm

Operational conditions 5.3 CR, air cooled

20 A. K. THAKUR AND A. K. KAVITI

Elfasakhany (2015)

Simeon (2015) [50] E0, E5, E10, E20, E30, E50, M0, M5, M10, M20, M30, M50

Kim et al. (2015)

26

27

28

[51] E0, E100

[49] E0, E3, E7, E10, Single-cylinder, M3, M7, M10, 4-stroke SI engine, EM3, EM7, EM10 65.1 mm bore, 44.4 mm stroke, 7 CR

Sayin et al. (2015)

25

4-cylinder, 4-stroke SI engine, 86 mm bore, 86 mm stroke, 143.5 mm connecting rod, 10.5 CR, 2000 cc displacement volume SI engine, 86 mm bore, 86 mm stroke, 9.5,13.3 CR, 500 cc displacement volume

Engine specifications Single-cylinder, 2 valves carburetted SI engine, 65.1 mm bore, 44.4 mm stroke, 7 CR, air cooled, 0.147 L displacement volume,79.5 mm connecting rod [48] ISB0, ISB10, ISB30, Single-cylinder, 4-stroke SI engine, ISB50** 88 mm bore, 64 mm stroke, 9 CR

Different blend compositions Ref. [47] E0, ISB3, ISB7, ISB10

Sl. no Study 24 Elfasakhany (2015)


(i) Highest CO emissions with E0 (ii) A decrease of 15.5%, 31% and 42% in CO emissions was observed with E3, E7 and E10 when compared with E0 (iii) The CO emissions of M3, M7 and M10 decreased by about 17.7%, 51.5% and 55.5%, respectively (iv) The CO emissions of EM3, EM7 and EM10 decreased by about 17.5%, 35.5% and 46.6%, respectively

(i) Decrease in CO emissions with increased CR (ii) Lowest CO emissions for ISB50 as an average of 27.62% compared to ISB0 at 11 CR

Engine speed 1000 rpm, 9.5, 13.3 CR, engine load- WOT Lambda ¡1.00

(i) CO emissions reduce by 28.3% on ethanol addition at CR of 9.5

–

–

(i) NOx emissions increase for higher percentages of ethanol and methanol to E30 and M30. (ii) NOx decreases after E30 and M30 (iii) Lowest NOx emissions were observed with E0 (i) NOx emissions increase by 10% on ethanol addition

(i) Increase in CO2 emissions with increased CR (ii) Highest CO2 emissions for ISB50 as an average of 30.56% compared to ISB0 at 11 CR (i) Lowest CO2 emission with E0 (ii) CO2 emissions of M3, M7 and M10 were higher than that for gasoline fuel by about 3%, 8% and 9.2%, respectively (iii) CO2 emissions of EM3, EM7 and EM10 were higher by about 3%, 5.1% and 7.1%, respectively (iv) CO2 emissions of E3, E7 and E10 are higher by about 1%, 1.7% and 4%, respectively, compared to E0 –

–

Results of research objects (different kinds of emissions) NOx CO CO2 – (i) Using ISB10 CO emissions (i) Using ISB10 CO2 emissions reduced by 43% compared to reduced by 30% compared to E0 E0 at 2600 rpm at 2600 rpm (ii) At 3400 rpm CO2 is lower as (ii) At 3400 rpm CO emissions compared with E0 by about exceed by 2.5% as compared to 27% E0

Full load, (i) CO emissions reduce for higher 1000–6500 rpm in steps of percentages of ethanol and 500 rpm methanol (ii) Lowest CO emissions for M50

2600–3450 rpm, load of 1.3–1.6 KW

2600 rpm, IgT-240 bTDC, WOT, 9, 10, 11 CR

Operational conditions 2600–3400 rpm

(continued)

(i) HC emissions increased on ethanol addition

(i) Decrease in HC emissions with increased CR (ii) Lowest HC emissions for ISB50 as an average of 28.13% compared to ISB0 at 11 CR (i) Highest HC emission with E0 (ii) The HC emissions of M3, M7 and M10 reduced by about 19.6%, 16% and 26%, respectively when compared with E0 (iii) HC emissions for E3, E7 and E10 reduced by about 3.5%, 14% and 21.5%, respectively (iv) HC emissions for EM3, EM7 and EM10 reduced by about 10.7%, 15.3% and 23.2%, respectively (i) HC emissions reduce for higher percentages of ethanol and methanol (ii) Lowest HC emissions for M50

HC (i) Using ISB10 HC emissions reduced by 21% compared to E0 at 2600 rpm (ii) At 3400 rpm HC emissions exceed by 7% as compared to E0

BIOFUELS 21

(i) NOx emission for ethanolgasoline blends is higher than gasoline – Maximum power (kW) 4.8 (i) CO emissions decrease with (at 3600 rpm), increasing ethanol percentage maximum torque (Nm) 4.71 (at 3600 rpm), 40%, 50%, 60%, 70%, 80%, 90%, 100% load conditions for constant engine speed

Results of research objects (different kinds of emissions) NOx CO2 (i) CO2 emissions increases; the (i) NOx emissions increase;. value at optimal input the value at optimal input parameters was 12.8 (%vol) parameters was 136.6 ppm CO (i) CO emissions reduced; the value at optimal input parameters was 3.5 (%vol)

[53] E0, E10, E20, E30 30

Banday et al. (2015)

Different blend compositions Ref. [52] E5, E7.5, E10, E12.5, E15 Sl. no Study 29 Najafi et al. (2015)


Engine specifications 4-cylinder SI engine, 71 mm bore, 83.6 mm stroke, 9.7 CR, 1323 cc displacement volume Single-cylinder, 4-stroke SI engine, 65.09 mm bore, 61.91 mm stroke, 123.82 mm Connecting rod, 9 CR, 206 cc displacement volume

Operational conditions Maximum power (kW) 47 (at 5200 rpm), maximum torque (Nm) 103 (at 2750 rpm)

(i) HC emission decreases at higher percentage load


HC (i) HC emissions reduced; the value at optimal input parameters was 1300 ppm

22

using the desirability approach of RSM. The emission characteristics of the engine improved significantly. An engine speed of 3000 rpm and a blend of 10% bioethanol and 90% gasoline (E10) were found to be optimal values. The results of this study revealed that at optimal input parameters, the values of the CO, CO2, HC and NOx were found to be 3.5 (% vol.), 12.8 (% vol.), 136.6 (ppm) and 1300 (ppm), respectively. Banday and Wani [53] investigated the effect of blending ethanol and gasoline in a single-cylinder four-stroke cycle SI OHV engine fitted to a generator. The simulation was done using professional engine simulation software from AVL Austria, named BOOST. AVL BOOST is used as a computational thermodynamic simulation tool to analyze the emission characteristics for different blends of ethanol and gasoline (10%, 20% and 30% ethanol by volume). The study was carried out for 40%, 50%, 60%, 70%, 80%, 90% and 100% load conditions at constant engine speed. Results were compared with those for pure gasoline. With an increase in ethanol content, CO decreased. Thus, E30 showed lower CO emission than the pure gasoline. With the increase in percentage load the fuel became leaner and resulted in a decrease in HC emissions. Further, initially the ethanol-gasoline blends showed higher HC emissions than gasoline because of the rich mixture, but at full load percentage HC emission was higher in pure gasoline than in the ethanolgasoline blends. The NOx emission increased with increasing load for all percentages of ethanol. With the increase of ethanol content in the gasoline the NOx emission increased, due to the oxygen content of the ethanol, as ethanol supplied addition oxygen for NOx formation. For comparison purposes, a summary of all the discussed emission parameters is given in Table 4.

Conclusion The aim of this review paper was to study the use of ethanol as a gasoline substitute and review the work done by researchers in the recent past. Ethanol-gasoline blends have the potential to be used as an alternative fuel that can effectively control the regulated emissions (CO, CO2, NOx and HC). Some key findings of this study are as follows: Tests were conducted at various percentages of blends, ranging from 0% to 100% ethanol. Based on the above observations, increasing the ethanol percentage to 20% showed a reduction in CO and HC emissions by 46.5% and 24.3%, respectively, in comparison to other percentages of ethanol, when tests were carried out at variable engine speeds ranging from 1000 to 4000 rpm. It was also observed that if the ethanol content in an ethanol-gasoline blend is increased to 10%, the HC and CO emissions decrease by 20.2% and

BIOFUELS

30.01%, respectively. When the ethanol content in the ethanol-gasoline blend exceeds 10%, HC and CO emissions increase and CO2 emissions decrease due to an increase in the temperature of the intake manifold and a decrease in the volumetric efficiency. Increasing the ethanol content reduced the CO2 emissions to 13.25%, 12.14%, 11.62%, 10.25% and 9.51% with E0, E25, E50, E75 and E100, respectively, when tests were conducted with CRs in the range of 6:1 to 10:1 at full load and by varying the engine speed in the range of 1500–4000 rpm at intervals of 500 rpm. Compared to unleaded gasoline, UHC emissions for ethanol and methanol decreased to about 22.79% and 28.22% on average at variable CRs. CO emissions also diminished to about 14.49% for ethanol blended fuels. It is very difficult to identify the optimum regulated emissions of ethanol-gasoline blends in a spark ignition engine. Researchers should develop techniques to optimize the emissions, which will be economical and save significant time and energy.

Disclosure statement No potential conflict of interest was reported by the authors.

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