A review on catalytic converter for automotive exhaust ... - IJSER.org

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through the exhaust valve. Sound waves and exhaust gas pass from exhaust manifold to Catalytic converter through a pipe. Hot exhaust gases entering inside.
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International Journal of Scientific & Engineering Research (IJSER) Volume 7, Issue 2, February 2016 ISSN 2229-5518

$UHYLHZRQFDWDO\WLFFRQYHUWHUIRUDXWRPRWLYH H[KDXVWHPLVVLRQ Dr.M.P Singh,Suman Raj Abstract:This paper illustrates the design of pollutant control system that is catalytic converter having dual bed with air injection for application in gasoline engine. High exhaust purification consisting of less harmful gases along with low sound waves moves out of the tail pipe. Keywords: Catalytic converter, exhaust emission conversion, thermodynamic model

IN TROD UCTION A d u al bed catalyst has tw o sep arate cham bers. Air can be injected in the m id d le of the catalyst to increase oxygen content in the back half of the converter. The engine can then be ru n slightly rich to im p rove N Ox red u ction in the front half of the converter. The air that is injected allow s high efficiency oxid ation of CO & H C in the back half of the converter. This typ e of converter can allow N Ox red u ction to occu r in th e front bed at m axim u m efficiency w hile CO and H C oxid ation are occu rring in the rear bed at m axim u m efficiency. It is the injection of air in front of the rear bed that allow s both oxid ation and red u ction to occu r at m axim u m efficiency. For the d u al bed catalyst to op erate at m axim u m efficiency, it m u st have very low oxygen levels in the exhau st entering the front bed . This only occu rs w hen the engine is ru nning slightly rich w ith no m isfires or d ep osit p roblem s. It m u st also have enou gh air injected in front of the rear bed to allow oxid ation of the CO and H C. The front bed of a d u al bed catalyst d oes also oxid ize CO and H C. Even a rich m ixtu re w ill leave som e oxygen in the exhau st. The catalyst u ses this sm all am ou nt of oxygen to oxid ize CO & H C into CO2 & H 2O. As N Ox is red u ced , oxygen from that N Ox is freed u p . If this extra oxygen w as allow ed to accu m u late it w ou ld start to lim it N Ox red u ction. Bu t the oxygen from the N Ox is u sed to oxid ize CO and H C. This lim its oxygen bu ild -u p in the front bed and keep s N Ox red u ction at m axim u m efficiency.

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A d u al bed catalyst d ep end s on air injection to p rovid e the oxygen to clean u p CO & H C w hen the m ixtu re is rich. Air is only injected into the rear bed . Many cars d o not have air injection. Withou t air injection and a slightly rich m ixtu re these cars m u st d ep end on som ething else to m anage the oxygen in the catalytic converter. THEORY OF D BAI H ot exhau st gas along w ith sou nd w aves generated at the end of exhau st stroke is sent to the exhau st m anifold throu gh the exhau st valve. Sou nd w aves and exhau st gas p ass from exhau st m anifold to Catalytic converter throu gh a p ip e. H ot exhau st gases entering insid e catalytic converter. Du e to p artial com bu stion the gases entering insid e the catalytic converter consists of a m ixtu re of carbon Monoxid e (CO) Unbu rned H yd rocarbons (H C) and oxid es of N itrogen (N Ox) w hich are harm fu l to the environm ent insid e the catalytic converter there consists of tw o ceram ic blocks w ith m icro d u cts consisting of p latinu m and rhod iu m in one block w hile p latinu m and p allad iu m in the other block acting as catalysts. The toxic gas enter into the first ceram ic block and heat u p sim u ltaneou sly. This cau ses the catalyst to react w ith the toxic gases. As the gas enters insid e the nitrogen m olecu les are the first to react. The catalyst cau ses the oxid es of nitrogen to reform into nitrogen and oxygen resp ectively. N Ox = O2 + N 2 The gas flow s throu gh the m icro d u cts of the second ceram ic block w here it react w ith the p latinu m and p allad iu m . Insid e the m icro d u cts of the second ceram ic

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International Journal of Scientific & Engineering Research (IJSER) Volume 7, Issue 2, February 2016 ISSN 2229-5518

block. H ere the carbon m onoxid e reacts w ith oxygen m olecu les to form carbon d ioxid e (CO2) CO + O = CO2 H C + O2 = CO2 + H 2O The u nbu rned hyd rocarbons also react w ith oxygen to form w ater and carbon d ioxid e. The exhau st gas now becom es less toxic and com es ou t from catalytic converter having m ixtu re of carbon d ioxid e (CO2) nitrogen (N 2) and w ater vap ou rs (H 2O). CON STRUCTION The catalytic converter consists of follow ing several com p onents THE CORE OR SUBSTRATE The core is often a ceram ic honeycom b in m od ern catalytic converters bu t stainless steel foil honeycom bs are u sed too.The honey-com b su rface increases the am ou nt of su rface area av ailable to su p p ort the catalyst and therefore is often called a catalyst su p p ort. THE WASHCOAT A w ash coat is u sed to m ake converters m ore efficient, often as a m ixtu re of silica and alu m ina. The w ash coat w hen ad d ed to the core form s a rou gh irregu lar su rface w hich has a far greater su rface area than the flat core su rfaces d o w hich then gives the converter core a larger su rface area and therefore m ore p laces for active p reciou s m etal sites. The catalyst is ad d ed to the w ash coat before being ap p lied to the core. THE CATALYST The catalyst itself is a p reciou s m etal. Platinu m is the m ost active catalyst and is w id ely u sed . It is no t su itable for all ap p lications how ever becau se of u nw anted ad d itional. Pallad iu m and rhod iu m are tw o other p reciou s m etals u sed . Platinu m and rhod iu m a re u sed as a red u ction catalyst w hile p latinu m and p allad iu m are u sed as an oxid ization catalyst TYPES OF CATALYTIC CON VERTER The tw o typ es of catalytic converter is d iscu ssed below : TWO-WAY CATALYTIC CON VERTER A tw o-w ay catalytic converter has tw o sim u ltaneou s tasks Oxid ation of carbon m onoxid e to carbon d ioxid e: 2CO + O2 →2CO2

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Oxid ation of u nbu rnt hyd rocarbons (u nbu rnt and p artially-bu rnt fu el) to carbon d ioxid e and w ater CxH 2x+2 + 2xO2 →xCO2 + 2xH 2O (com bu stion reaction) This typ e of catalytic converter is w id ely u sed on d iesel engines to red u ce hyd rocarbon and carbon m onoxid e em issions. THREE-WAY CATALYTIC CON VERTER A three-w ay catalytic converter has three sim u ltaneou s tasks: Red u ction of nitrogen oxid es to nitrogen and oxygen: 2N Ox →xO2 + N 2 Oxid ation of carbon m onoxid e to carbon d ioxid e: 2CO + O2 →2CO2 Oxid ation of u nbu rnt hyd rocarbons (H C) to carbon d ioxid e and w ater: CxH (2x+2)+ 2xO2 →xCO2 + 2xH 2O These three reactions occu r m ost efficiently w hen the catalytic converter receives exhau st from a n engine ru nning slightly above the stoichiom etric p oint. This is betw een 14.6 and 14.8 p arts air to 1 p art fu el by w eight for gasoline.Generally engines fitted w ith 3-w ay catalytic converters are equ ip p ed w ith a com p u terized closed loop feed back fu el injection system em p loying one or m ore oxygen sensors, thou gh early in the d ep loym ent of 3-w ay converters, carbu retors equ ip p ed for feed back m ixtu re control w ere u sed . While a 3-w ay catalyst can be u sed in an op en-loop system , N Ox red u ction efficiency is low . Within a narrow fu el/ air ratio band su rrou nd ing stoichiom etry, conversion of all three p ollu tants is MOD EL OF THREE-WAY CATALYTIC CON VERTER The m athem atical m od el of a catalytic converter contains tw o elem ents. The first is the kinetic reaction m od el and the second is the transp ort equ ations for the m ass, m om entu m and energy. We u sed a kinetic m od el based on the m echanistic step s. The transp or t m od el w as based on the m od eling of a single channel of the converter. THE KIN ETIC MOD EL We consid er a reaction schem e rep resented by a set of fou r global reactions: 2CO + O2 →2CO2 2CO + 2N O →N 2 + 2CO2 C2H 4 + 3O2 →2CO2 + 2H 2O C2H 2 + 2.5O2 →2CO2 + H 2O

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International Journal of Scientific & Engineering Research (IJSER) Volume 7, Issue 2, February 2016 ISSN 2229-5518

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d ilu ted exhau st gas in system s com p rising a p ositive d isp lacem ent p u m p is calcu lated w ith the follow ing form u la : V = Vo x N w here, V = Volu m e of d ilu ted exhau st gas exp ressed in m 3/ test (p rior to correction) Vo = Volu m e of gas d elivered by the p ositive d isp lacem ent p u m p on testing Cond itions, in m 3/ rev. N = N u m ber of revolu tions p er test.

EXPERIMEN TAL SET UP

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THERMOD YN AMIC MOD EL

CALCULATION OF THE MASS EMISSION S OF POLLUTAN TS The calcu lation p roced u res for the m ass em ission of p ollu tants and correction for hu m id ity for oxid es of nitrogen. The m ass em ission of p ollu tants are calcu lated by m eans of the follow ing equ ation: 𝑉𝑚𝑖𝑥 ×𝑄𝑖 ×𝐾ℎ ×𝐶𝑖 ×10−6

𝑀𝑖 = 𝑑 Mi = Mass em ission of the p ollu tant i in g/ km Vm ix = Volu m e of the d ilu ted exhau st gas exp ressed in m 3/ test and corrected to stand ard cond itions 293K and 101.33 kPa Qi = Density of the p ollu tant i in kg/ m 3 at norm al tem p eratu re and p ressu re (293 K and 101.33 kPa) kH = H u m id ity correction factor u sed for the calcu lation of the m ass em issions of oxid es of nitrogen. There is no hu m id ity correction for H C and CO. Ci = Concentration of the p ollu tant i in the d ilu ted exhau st gas exp ressed in p p m and corrected by the am ou nt of the p ollu tant i contained in the d ilu tion air. d = d istance covered in km VOLUME D ETERMIN ATION Calcu lation of the volu m e w hen a variable d ilu tion d evice w ith constant flow control by orifice or ventu ri is u sed . Record continu ou sly the p aram eters show ing the volu m etric flow and calcu late the total volu m e for the d u ration of the test. Calcu lation of volu m e w hen a p ositive d isp lacem ent p u m p is u sed The volu m e of

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THERMOD YN AMIC MOD EL OF THE TWC Figu re show s a sketch of heat and m ass transfer and cross sectional geom etry of the TWC. Tw o gas p hases and one solid p hase have been consid er ad d itionally m ass is exchanged w ith the second gas p hase by m e ans of rad ial d iffu sion. The inner (second ) p hase contains w ash coat and bou nd ary layers. H ere no axial convection occu rs. Mass is exchange in the rad ial d irection w ith the ou ter gas p hase on the one hand by m eans of d iffu sion and w ith the solid su rface on the other hand by m eans of ad sorp tion or d esorp tion.

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PROCESS MOD EL OF THE TWC The TWC m od el p resented in the follow ing is referred to as the p rocess m od el becau se its goal is to u nd erstand the m ost im p ortant d ynam ics as d escribed above rather than the u se in a control system . The m od el shou ld be able to rep rod u ce the d ynam ic inp u t-ou tp u t behavior of all m easu red sp ecies. The concentrations of N O, CO, H C, CO2, H 2, O2, H 2O, and N 2 have been consid ered . Since only the total H C concentration cou ld be m easu red . The cross sectional d istribu tions of the flow velocity tem p eratu re and concentration p rofiles in the exhau st u p stream of the TWC have been assu m ed to be u niform . In reality this is hard ly the case. H ow ever the focu s here is on the m ain d ynam ic p henom ena rather than on the TWC’s overall p erform ance w hich can be significantly influ enced by the flow velocity p rofile. H ence only one channel has been m od eled u sing a oned im ensional ap p roach. Geom etry and m aterial p aram eters su ch as storage cap acities have been assu m ed to be constant along the flow axis. In reality ageing m echanism s close to the inlet are d ifferent from those close to the ou tlet of the TWC. At the inlet TWC d eactivation occu rs m ainly becau se of p oisoning. Tow ard s the tail m ore therm al effects are d om inant su ch as sintering. Ad d itionally d eactivation d oes not occu r u niform ly on the TWC cross section it is rather d ep end ent on the exhau st gas flow velocity p rofile at the inlet of the TWC. All p henom ena eventu ally lead to a red u ction of the oxygen storage cap acity. The cross sectional flow velocity p rofile in one channel is not constant along.

GOVERN IN G EQUATION S The p hysical m od el of the catalytic converter u nd er stu d y is show n in Fig. w here the stagnation -p oint flow geom etry is u sed . A m ixtu re of gases and air d escribed by the m ass concentrations and flow s w ith a velocity grad ient and tem p eratu re p erp end icu lar to a p latinu m p late of finite thickness The low er su rface of the p late is kep t to the sam e tem p eratu re.

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The bou nd ary layer governing equ ations for the assu m ed frozen gas-p hase are the follow ing 𝜕(𝜌𝑢) 𝜕(𝜌𝑣) + =0 𝜕𝑥 𝜕𝑦 𝜕𝑢 𝜕𝑢 𝜕 𝜕𝑢 𝜌𝑢 + 𝜌𝑣 = (𝜇 ) + 𝜌∞ 𝑎2 𝑥 𝜕𝑥 𝜕𝑦 𝜕𝑥 𝜕𝑦 𝜕𝑇 𝜕𝑇 𝜕 𝜕𝑇 𝜌𝑢𝐶𝑝 + 𝜌𝑣𝐶𝑝 = (𝜆 ) 𝜕𝑥 𝜕𝑦 𝜕𝑥 𝜕𝑦 Where u and v are the longitu d inal and transversal com p onents of velocity, resp ectively ρ , μ, Cp , λ and are the d ensity, viscosity, sp ecific heat at constant p ressu re, and therm al cond u ctivity of the gas-p hase m ixtu re. Di corresp ond s to the d iffu sion coefficient of sp ecies. In Figu re ε = Gas void fraction ρ g= Channel gas d ensity Cp g= Sp ecific heat cap acity Ageo= Sp ecific geom etry catalyst su rface Εw c= w ashcoat p orocity ρ w c= w ashcoat gas d ensity Acat= Sp ecific catalytic active su rface Di= Rad ial m ass transfer coefficient Flow is lam inar and constant sherw ood nu m ber is

𝑆ℎ𝑑 =

𝐷𝑖 𝑋 𝐷𝑐ℎ𝑎𝑛 𝐷𝑖𝑁2

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= 2.47

DiN 2 = binary d iffu sion coefficient of the sp ecies i in N 2. It w as calcu lated by Fu ller et.al.The m ass balance for sp ecies i in the inner gas p hase d oes not contain any convective or axial d iffu sion term only rad ial m ass transp ort occu rs. On the channel sid e m ass is exchanged w ith the channel p hase by m ean of rad ial d iffu sion.On the solid su rface sid e m ass is exchanged by m eans of ad sorp tion and d esorp tion. The m ass balance for gas channel can be w ritten as ρ𝑔 𝜀

𝛿𝑤𝑖

𝛿2𝑤𝑖

𝑚 𝛿𝑤𝑖

= 𝜀 𝐷𝑒𝑓𝑓 − 𝛿2𝑥 𝐴𝑐𝑠 𝛿𝑥 −𝐷𝑖 𝐴𝑔𝑒𝑜 (𝜌𝑔 × 𝑤𝑖 − 𝜌𝑤𝑐 × 𝑣𝑖) + 𝑊𝑖 ∑(𝐷𝑖 × 𝐴𝑔𝑒𝑜 (𝜌𝑔 × 𝑤𝑖 − 𝜌𝑤𝑐 × 𝑣𝑖)) 𝛿𝑡

CON CLUSION The nu m erical m athem atical m od eling of a catalytic converter is d evelop ed in this p ap er. The catalytic com bu stion m od el is for a m ixtu re of CO, N O and air, u sing the stagnation -p oint flow geom etry. The p rop osed chem ical reaction m echanism is able for red u cing N O and oxid ation of CO.

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REFEREN CES 1) Eberhard Jacob, Rheinhard Lam m erm ann, And reas Pap p enherim er, Diether Rothe – Exhau st Gas Aftertreatm ent System for Eu ro 4: H eavy Du ty Engines‖ – MTZ 6/ 2005 2) K.V.R.Babu , Chris Dias, Shivraj Waje, Alfred Reck, Kim Wonsik – PM Metalit – A Continu ou sly Regenerating Partial Flow Particu late Filter Concep t and Exp erience w ith Korean Retrofit Program m e SAE Technical Pap er 2008- 28-0008 3) Sou gato Chatterjee, And rew P. Walker, Philip G.Blakem an – Em ission Control Op tions to Achieve Eu ro IV and Eu ro V on H eavy Du ty Diesel Engines, SAE Technical Pap er 2008-28-0021. 4) Otto A. Lu d ecke et al (1983) Diesel Exhau st Particu late Control System Develop m ent, SAE Pap er 830085. 5) Allan C. Lloyd , Diesel Engines Environm ental Im p act and Control, DEER Conference 2002. 6) Jacobs, T.Chatterjee, S.Conw ay, R.Walker A.Kram er, J.And Mu eller-H aas, K. Develop m ent of a Partial Filter Technology for H d d Retrofit SAE Technical Pap er 200601-0213. 7) Jinke Gong, Longyu Cai, Weiling Peng and Jingw u Liu ,Yu nqing Liu , H ao Cai and Jiaqiang E Analysis to the Im p act of Monolith Geom etric Param eters on Em ission Conversion p erform ance Based on an Im p roved Threew ay Catalytic Converter Sim u lation Mod el, SAE p ap er 2006-32-0089 (2006)

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8) Bassem H . Ram ad an and Philip C. Lu nd berg, Characterization of a Catalytic Converter Internal Flow , SAE p ap er, 2007-01-4024 (2007) 9)Karthikeyan,S.H ariganesh,R.Sathyanand an,M.Krishnn S.Com p u tational and Exp erim ental Investigation on After-Tream ent System s to Meet Futu re Em ission N orm s for Tru ck Ap p lications International Jou rnal of Engineering Science and Technology, 3(4),3314-3326 (2011) 10) Ku m ar Krishan and Aggarw al M.L. A Finite Elem ent Ap p roach for Analysis of a Mu lti Leaf Sp ring u sing CAE Tools, Research Jou rnal of Recent Sciences, 1(2), 9296,(2012) 11) Dev N ikhil, Attri Rajesh, Mittal Vijay, Ku m ar Sand eep , Mohit, Satyap al and Ku m ar Pard eep Therm od ynam ic Analysis of a Com bined H eat and Pow er System , Research Jou rnal of Recent Sciences, 1(3),76-79 (2012) 12) P.Pu nd ir,Engine em issions p ollu tant Form ation and Ad vances in Control Technology, N arosa Pu blishing hou se, N ew Delhi, Chap ter -1, p p . 1-10 13) Ganesan,V.2004, Internal Com bu stion Engines 14) Mathu r and sharm a I.C Engine

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