Mar 19, 2012 - of Diesel Engine Emissions, Journal of the Air Pollution Control Association, 12:11, 516-546, DOI: ..... which diverted 30 cc per minute of gas.
Journal of the Air Pollution Control Association
ISSN: 0002-2470 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/uawm16
Measurement of Diesel Engine Emissions Herbert C. Mckee , John M. Clark & Ralph J. Wheeler To cite this article: Herbert C. Mckee , John M. Clark & Ralph J. Wheeler (1962) Measurement of Diesel Engine Emissions, Journal of the Air Pollution Control Association, 12:11, 516-546, DOI: 10.1080/00022470.1962.10468122 To link to this article: https://doi.org/10.1080/00022470.1962.10468122
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MEASUREMENT of DIESEL Engine EMISSIONS1 HERBERT C. MCKEE, JOHN M. CLARK, and RALPH J. WHEELER, Southwest Research Institute, San Antonio, Texas
• he recent adoption of regulations concerning automobile exhaust emissions by the State of California1 has focused attention on automotive air pollution on a national scale. One result of this activity-has been that questions were raised concerning the possibility of regulations to be applied to diesel powered vehicles. The California standards specify "motor vehicle exhaust emissions" and thus could be assumed to apply to all vehicles. The State Motor Vehicle Pollution Control Board has so far limited its enforcement activities to the development of a program to control automobile emissions, although the problem of diesel engine emissions is being studied. The testing procedures specified for the evaluation of automobile exhaust control devices are based on extensive data in the literature on automobile exhaust emissions, and thus were not intended to be used to measure diesel exhaust emissions or to evaluate control devices intended for use on diesel engines. Due to differences in the design and operation of diesel engines, it is probable that different methods of measurement should be used. This paper will outline the differences between conventional automobile engines and diesel engines, to see how these differences may affect potential air pollution problems, and will present data comparing different methods of measurement which are available for determining the amount and nature of diesel engine emissions. Several literature references are found describing work on diesel engine exhaust, although the amount of work is only a very small fraction of that performed to study automobile exhaust. Most of the previous investigations of diesel exhaust were concerned with smoke and odor, since these manifestations are most obvious to the general public. Due to the lack of good experimental methods to study smoke and odor, especially odor, the knowledge available concerning these * Presented at the 55th Annual Meeting of APCA, Sheraton-Chicago Hotel, May 20-24, 1962, Chicago, Illinois. 516
problems and their control is less than would be desired. Very little attention has been paid to the hydrocarbon content of diesel exhaust. The most complete study appears to be that of Elliott, Nebel, and Rounds of the General Motors Research Laboratories.2 They compared the exhaust composition of diesel, gasoline, and propane-powered motor coaches, measuring carbon monoxide, oxides of nitrogen, formaldehyde, and total hydrocarbons. The hydrocarbon determinations were made with a mass spectrometer and showed average concentrations from 90 to 390 ppm for the diesel-powered vehicles, depending on engine operating conditions. The maximum single value for a diesel was 610 ppm, obtained with one of the vehicles during deceleration. These values, when compared with the values for gasoline and propanepowered vehicles and with other data in the literature on automobile engines, certainly indicate that the hydrocarbon content of diesel exhaust is quite low compared to other types of automotive power plants. Nevertheless, in view of the recent actions to control motor vehicle exhaust emissions, it seemed desirable to make some
further investigation of hydrocarbon emissions. A primary objective in this work was to determine what shortcomings might exist in attempting to measure diesel emissions by a procedure similar to that specified bj' the Calkfornia Motor Vehicle Pollution Control Board for automobile exhaust control devices. Characteristics of Diesel Engines
In order to compare the combustion characteristics of diesel engines with conventional automobile engines, it is helpful first of all to review the basic principles of operation of each type. Conventional passenger car engines operate on the Otto cycle, in which a spark plug is used to ignite a combustible homogeneous mixture of gasoline and air in the cylinder. The ratio between the amount of gasoline and air in the mixture is controlled rather closely, since combustion cannot be maintained if the mixture is either too lean or too rich. In general, the usable combustible limits range from approximately 90 to 120% of the chemically correct or stoichiometric fuel/air ratio. The action of the carburetor plus the turbulence and mixing which
TO IR OR FREEZEOUT TRAP
RECORDER
f
SAMPLE PROBE TO ENGINE EXHAUST
I3x MOLECULAR SIEVE FILTER
Fig. 1.
Schematic diagram of sampling and analytical system. Journal of the Air Pollution Control Association
Table I—Typical Calculation of Exhaust Emission (Engine C) Measured Concentrations HC, Weighting Weighted Values , Mode ppm° CO, %» co , %h Factor HC, ppm CO, % co , % 2 2 0.42 1.4 0.042 0 10 0 0.06 Idle 30 0 0 0-25 10.0 0.185 5.55 1.85 0 11 0 30 10.2 0.061 0.67 0.64 15 0 8.0 0 30-15 0.033 0.50 0.26 15 0 8.0 0 15-30 0.455 6.83 3.68 40 8 0.5 12.2 0.042 0.34 0.021 0.51 50 15 0.8 12.7 0.015 0.23 0.012 0.19 20 0.6 50-20 11.3 0.029 0.58 0.017 0.33 30 0 0 20 10.0 0.050 1.50 0.50 12 0 6.0 0 30-0 0.029 0.35 0.17 0.1 18 0-60 10.0 0.059 1.06 0.006 0.59 0.056 1.000 18.03 8.78 Composite values: Hydrocarbons—18 ppm CO—0. 0 6 % CO2—8. 8% As indicated by infrared analysis of freezeout samples. As indicated by Orsat analysis. occurs in moving the air and fuel mixture from the carburetor through the intake manifold into the cylinder is sufficient so that for all practical purposes the cylinder is filled with a homogeneous mixture of fuel and air when ignition occurs near the top of the compression stroke. The spark initiates a flame front which progresses away from the point of ignition in approximately a spherical pattern. This progression of the flame front through the combustion volume occurs at a finite rate of speed, usually 100 to 150 feet per second depending on the fuel/air ratio. This relatively slow combustion of the fuel permits the piston to move down and expand the combustion volume prior to completion of combustion. This effectively lowers the peak pressures and temperatures achieved in the Otto cycle from what would occur if all combustion occurred while the piston was near or at the top of the stroke. A diesel engine, on the other hand, works in quite a different manner. Fuel and air are not mixed prior to being passed into the cylinder. Rather, air alone is drawn in through the intake valve and is compressed to a high pressure and temperature by the compression stroke. Fuel is then injected as a spray into the top of the combustion zone; after a certain time interval, known as the ignition delay period, combustion is initiated simultaneously in a multiple number of points throughout the combustion chamber due to the high temperature and pressure. Combustion starts along the edges of the spray where the fuel/air ratio is sufficiently close to the stoichiometric value to initiate combustion. Mixing of the fuel droplets and the oxygen in the combustion chamber results in very rapid completion of the combustion process. This multiple point simultaneous ignition results in a sudden release of energy which rapidly November 1 962 / Volume 1 2, No. 11
raises the pressure within the combustion chamber before the piston can move to expand the charge in the combustion volume. This quick burning prior to expansion, together with the higher inherent compression ratio of the diesel, generates peak pressures and temperatures during combustion that may be two or three times those experienced in a comparable Otto cycle engine. Another important factor is that, so far as the over-all charge within the cylinder is concerned, a large excess of oxygen is present. In fact, a diesel cycle normally operates with an amount of fuel ranging from almost zero to perhaps 60% of the stoichiometric ratio, although in the zone immediately around the fuel spray where combustion is initiated the composition approaches the stoichiometric ratio. In high output diesel engines, it is economically feasible to utilize a turbocharger. This is a centrifugal blower driven by the exhaust gases passing through a turbine wheel, which serves to compress the air entering the intake manifold. This provides a greater supply of air at higher pressures than is the case with the naturally aspirated engine without a turbocharger. The excess air permits more fuel to be injected to provide additional power and still maintain usable air-fuel ratios. Other details of operation of this cycle are essentially the same, but increasing the pressure of the intake air serves to further increase the peak pressures and temperatures achieved during combustion. In summary, the diesel engine when compared to the conventional automobile engine is characterized by (1) combustion in the presence of an excess of oxygen and (2) higher pressures and temperatures during combustion. These differences in combustion characteristics result in many differences in the exhaust and blowby
emissions produced by diesel engines and therefore in the potential air pollution problems which such engines cause. Experimental Procedure In connection with other test and development work on diesel engines, tests were made to determine the hydrocarbon concentration of exhaust and blowby. The type and number of engines available and the amount of sampling that could be performed were not sufficient to provide a statistically significant estimate of the total diesel emissions in an average city, and no interpretations of this nature are warranted. However, the data do indicate the general range of concentration encountered. More important, comparisons can be made between different methods of hydrocarbon measurement to indicate the advantages and limitations of the different techniques. Supplementary work was also performed to evaluate possible errors due to condensation in the sampling system. When possible, hydrocarbon concentrations were measured over a driving cycle similar to the method specified by the State of California for evaluation of automobile exhaust control devices. In other cases, sampling was conducted on engines being used for other tests; for this work, speed and load conditions were specified by the other test conditions, and sampling was conducted in portions of the cycle that produced operating conditions of possible interest in considering air pollution problems. The following engines were used in this work: Engine A. An experimental four-cycle, divided chamber engine, similar in combustion characteristics to conventional diesel engines used in trucks, naturally aspirated. Engine B. The same as Engine A, but equipped with a turbocharger. Engine C. Another experimental fourcycle engine, open chamber, naturally aspirated. Engine D. The same as Engine C, but equipped with a turbocharger. Engine E. A single-cylinder research diesel engine, naturally aspirated. Engine F. A supercharged version of Engine E. Engine G. A large 2-cylinder, two-cycle, research diesel engine. Measurements of the hydrocarbon content of exhaust and blowby streams were made with three different methods in order to obtain a comparison be517
tween these methods. The instruments used were the following: (1) Liston-Becker Model 15A nondispersive infrared gas analyzer with n-hexane detector and Varian Model Gil, 0 to 10 mv strip chart recorder. (#) A Carad flame ionization analysis detector and Texas Instruments PSR 0 to 5 mv strip chart recorder. (FIAD) (3) A Perkin-Elmer Model 21 recording infrared spectrometer and one-meter gas cell. The Perkin-Elmer instrument was used to calibrate the other two instruments and to analyze for ethylene and acetylene in the grab samples and freezeout samples which were collected during engine operation. The Perkin-Elmer instrument was calibrated by expanding a known volume of hexane vapor into the gas cell and allowing the cell to come to atmospheric pressure. The sample was then scanned in the region from three to four microns and the optical density obtained. The procedure was repeated using ethylene and acetylene, scanning from 10 to 11 and 13 to 14 microns, respectively. The calibration curves for the other two instruments were obtained by passing mixtures of air or nitrogen and n-hexane through the instruments and simultaneously collecting a sample in the one-meter gas cell. The sample was then scanned on the Model 21 in the same manner as used for calibration of that instrument. Figure 1 illustrates the sampling system used for the flame ionization detector and the nondispersive infrared instrument. A ' pump was provided to pull the sample through a short sampling probe placed in the exhaust line, through a water trap, and fiberglass filter, into the pump. . The sample then went through a sample splitter which diverted 30 cc per minute of gas through the flame ionization detector and allowed the remainder to' flow through the infrared instrument. The flow through the flame ionization detector was measured by, a flow meter and controlled by two needle valves in series, since the flow, rate to this instrument is critical. Hydrogen for the flame ionization detector was ^controlled by a pressure regulator and needle valve,.and measured with a flow meter. Freezeout samples for analysis • oh the Model 21 infrared instrument were obtained by pulling one liter of gas per minute through an ascarite trap for CO2 removal and then through a fiberglass packed U-trap immersed in liquid nitrogen, sampling for a total 518
Table II—Summary of Exhaust Hydrocarbon Emissions Hydrocarbon, ppm
Engine
(A) (B) (C)
CO, %c
CO*. oc
°/
I—Weighted averages, 11-mode cycle Experimental, naturally 26« aspirated Experimental, turbocharged 122« Experimental, naturally 176 aspirated 18
0
5 .8
0.05 0.06
6.,0 8..8
35'J 35
4.02 4.02
7,.4 4
(D) . Experimental, turbocharged II—Values at stated speed and load Speed/load
(F)
(G)
a b •
c
One-cylinder, supercharged accel. Two cylinder two-cycle accel.
500/0 500/0 to 1000/0 1800/max 250/0 250/max to 835/max 835/max
35 a 175° ONS MEASUREMENT (Continued from page 521)
Bay. Area
Acting in line with its motto "Air Pollution Control Is Everyone's Business," the six-county Bay Area Air Pollution Control District has established a Message Center in Alameda County to facilitate communication between local citizens and public agencies, and the District. Located in the Alameda County Health Department Building, San Leandro, the Center will receive local complaints of air pollution sources and requests for assistance, and will serve as a headquarters for meetings with violators and parties requiring help with compliance programs. A conference room will be provided for this purpose. "With Message Centers located in the counties," explained Bay Area APCD Director of Enforcement, Joseph Coons, BY-LAW CHANGES APPROVED "the District hopes to strengthen its liaison with public agencies and with The APCA membership has approved private citizens, eliminating the long the following changes to the By-Laws: distance communications formerly necThe first amendment is a statement to essary in reporting air pollution probbe incorporated in Article III, Section 1 lems." as subparagraph (k). The third in a series of regular meet"Provide a forum for the expression ings of the Board of Directors of the of different viewpoints and the climate Bay Area Air Pollution Control District for the resolution of differences relatscheduled in the member counties to ing to atmospheric pollution." alternate with those at the District The second By-Law Amendment has headquarters in San Francisco, was held to do with the authorization for formain San Mateo's County Supervisors tion of local sections and the rules under Chambers. which they will operate. This amendIn an outline of the District's high ment was proposed to become Article priority drives aimed at full correction, XVII of the By-Laws entitled "Local a tight compliance schedule or legal Sections" and encompasses two paraprocess, a progress report on Owensgraphs. Corning Fiberglas anti-smog installations stated that 16 of the plant's 29 air "(a) It shall be the policy of the pollution sources have been corrected, Association to encourage the organizaand by the final correction date May tion of local sections of the national 1963, the total clean-up program will body to carry out on a local level the have cost more than one million dollars. functions and objectives of the It was predicted that by July 1, 1963, Association. drives will be in full operation on 1083 "(b) The Board of Directors shall industries, including nonferrous melting formulate a set of 'rules for local plants, paint spraying operations, chemsections' which set forth the proical manufacturers, food industry operacedures and requirements necessary tions, and wood waste burners. for the formation, administration, and operation of local sections of the New York City Association." Apartment house owners and superThe proposed amendments were pubintendents are being notified by Comlished in the March 1962 Journal of the missioner Arthur J. Benline of the DeAir Pollution Control Association. The partment of Air Pollution Control of the amendments were discussed at the Department's continuing drive against membership meeting held in Chicago, pollution from domestic incinerators. May 22, 1962. Building owners have an obligation to instruct their superintendents, janitors, Tabulation Results and porters in the principles of incineraAmendment to Article III, Section 1 tor operation and maintenance. Smoke, as subparagraph (k): approved—772; fly-ash, and odors adversely affect the disapproved—24. buildings in which the incinerators are By-Law amendment to become Artilocated, just as they do adjoining buildcle XVII, entitled "Local Sections:" ings, by creating costly cleaning probapproved—762; disapproved—35. lems, discomfort to tenants, and they are a health menace. Incinerator burning is legal only beCommissioner Benline offers to send tween the hours of 7 A.M. and 5 P.M. the Department's leaflet, "Tips on Only incinerators with full automatic Incinerators," in either English or controls may be operated at other hours Spanish, free of charge, to any landlord under special permit from the Departor tenant who requests it from Publicament. Violators are liable to court tions, Department of Air Pollution summons which may result in a fine up Control, 15 Park Row, New York 38, to $100 for the first offense. New York. 546
comparing results with a naturally aspirated engine with results obtained with a turbocharged engine, under conditions of acceleration. Since the turbocharger is operated by exhaust gases, rapid acceleration caused an excess of fuel to be injected, until the increase in engine rpm provided enough exhaust gases to allow the turbocharger to accelerate and produce sufficient air flow to match the increased fuel flow. Before this occurred, however, the engine operated for a brief period with an insufficient supply of air, compared to the excess of air normally present. Since acceleration conditions comprise a major portion of the recommended operating cycle, this difference is important in comparing overall emissions from a naturally aspirated engine and a turbocharged engine. If this factor becomes important because of possible effects on community air pollution problems, design of turbocharged diesel engines to prevent a sudden increase in fuel flow during acceleration might be considered; this could be accomplished without unduly affecting performance. REFERENCES
1. Diana Clarkson and John T. Middleton, "The California Control Program for Motor Vehicle Created Air Pollution," / . Air Poll. Control Assoc, 12: 1, 22-28 (January 1962). 2. Martin A. Elliott, George J. Nebel, and Fred G. Rounds, "The Composition of Exhaust Gases from Diesel, Gasoline and Propane Powered Motor Coaches," J. Air Poll. Control Assoc, 5: 2, 103-108 (August 1955). 3. Robert L. Beatty, L. B. Berger, and H. H. Schrenk, "Determination of Oxides of Nitrogen by the Phenoldisulfonic Acid Method," B. I. 3687, U. S. Bureau of Mines (February 1943). 4. P. R. Lepisto, H. C. McKee, K. D. Mills, and R. J. Wheeler, "Hydrocarbon Emissions from Automobiles," Report No. 32, Air Pollution Foundation, San Marino, California (February 1961).
W. L FAITH CONSULTING CHEMICAL ENGINEER
—REPORTS —SURVEYS —EVALUATION AIR POLLUTION PROBLEMS 2540 Hunfington Drive, San Marino, Calif. Tel: Atlantic 7-9383 (Area Code-213)
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