Published on

  • Be the first to comment

  • Be the first to like this

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide


  1. 1. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408 Numerical Analysis Of Surface Reaction Of Catalytic Converter B. JOTHITHIRUMAL,1 Dr .E. JAMES GUNASEKARAN2, CHANDAN DEY3, Assistant professor, Associate professor, Research Scholar Dept. of Mechanical Engineering Annamalai UniversityABSTRACT Pollution has become a major problem converter components is playing a very vital acrossthroughout the world. The automotive pollution the world.Literature review reveals numerousis responsible highly for the global climatic publications on two-and three- dimensionalchanges since fifties increased concentration of computational fluid dynamic(CFD) modelling of apollutants in the vehicle emissions poses a single channel of the monolith(Canuserious health hazards to the public. &Vecchi,2002;Chatterjee, Deutschamnn, &Consequently, the air (prevention & control of Warnatz, 2001; Deutschamnn, Maier,Riedel,pollution) act was passed in India in 1981, and Stroemann, & Dibble, 2000;Grimm &its amendments and emissions control Mazumder,2008; Groppi, Belloli, Tronconi,regulations became stringent step by step. Due &Forzatti, 1995; Holder, Bolliga,Anderson,to increasingly stringent government regulations &Hochmuth, 2006; Mantzaras, Appel, & Benz,on vehicle nitrogen oxides (NOx) emission levels 2000; Papadias, Zwinkels, Edsberg, & Bjormborg,the selective catalytic reduction (SCR) of NOx to 1999; Raja, Kee, Deutschmann, Warnatz, &N2 by hydrocarbons has gained a great deal of Schmidt,2000; Sallamie &Koshkanab, 2003;attention. Catalytic converters for petrol driven Young & Finlayson, 1976, among manypassenger car have now become mandatory for others).Recently, due to the shortage of betternew cars and SCR with ammonia water alternatives,the knowledge gained from theinjection system is used to reduce the exhaust simulation of a single channel is extrapolated to thepollution. entire catalytic conveter.Since the channels are The project work reports some result of coupled to each other through heat transfer,andinvestigations carried out on the operation of individual channels may encounter different flowammonia water injection system on exhaust rates,extrapolation of the results of a single channelcarried out by simulation model to reduce the to the entire converter is not always accurate,andNOx formation. The present work was done on may lead to flawed designs(Tischer,correa &simulation model of catalytic converter on duetschmann,2001).Shuai and wang (2004)exhaust system using Comsol multiphysics modelled the monolithic reactor using a twosoftware. This project report describes the use dimensional model,in which the reactor wasof catalytic converter and injected ammonia modelled as a porous medium and surface reactionswater to reduce the harmful exhaust gas. were modelled using a two step mechanism.Kolaczkowski and Serbertsioglu(1996)Keywords: monolith reactor,NOx,NO,Ammonia performed analytical modelling of channel interactions in catalytic combustion reactors.The1.INTRODUCTION focus of their study was the effect of monolith The reduction of Automobile pollution material properties on heatusing catalytic converter in the latest vehicle speaks dissipation.Chen,Alexio,Williams,Leprince,andin high volume towards its successes. The uses of Yong(2004)performed three dimensional CFDcatalytic converter are becoming compulsory for all modelling of flow and heterogeneous reactions inthe heavy vehicles in order to prevent global catalytic converters.The pressure and velocitywarming. The modelling of catalytic converter as fields were calculated by modelling the monolith aswell as its simulation of surface reaction is very a porous medium. The surface reaction model wasimportant to determine the conversion rate or the then superimposed on the fluid flow results.Teamount of pollutants reduction in the core of objective of the present study is to demonstrate thecatalytic converter of the flue gasses from the effectiveness of a new implicit coupled for suchengines. The catalytic converter model is large scale catalytic converter.simulating for the implementation of new catalytic This paper describes how the modelling ofconverter technology. For this aspect, the role of catalytic converter has done using plug flow reactorexhaust gas after treatment method for the catalytic to obtain its high efficiency while simulating the model, the characteristic graphs of various inlet 399 | P a g e
  2. 2. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408temperatures on what the changes in molar flowrate, selectivity parameters, temperature profilesetc.With the results this paper illustrates about thechanges of different parameters of fluid like molarconcentrations, temperature distributions,isosurface etc.which represents the conversions ofpollutants like SOx and NOx in its monolithiticreacting surface made up of materials zeolite andkaoline.While on the designing the catalyticconverter model the important issue is the impactsof scale up or scale down of the catalyticconverter,that is what happens if the overalldimensions of the catalytic converter is going toincrease or decrease,keeping the channeldimensions unchanged?This is a critical question FIG: 1 SIMULATION MODEL FOR THE MULTIwhich has to be answered by modelling and CHANNELsimulation in order to keep design cost low.2.COMPUTATIONAL METHOD The modelling of catalytic converter isdone here using comsol multiphysics software. The3D model of the catalytic converter is drawn herewith its inlet, outlet, inlet walls, outlet walls,reactor surface boundaries, and the domains likesupporting walls &channel blocks. The 2D objectof 100 mm dia circle with its channel blocks isextruded up to 470mm to represent the 3D model of catalyticconverter with its reactor surface. In the process ofsimulation It is used the „standard SCR‟ reaction4NH3+4NO+O2→4N2+6H2O----------------------(1)In the absence of oxygen, to reduce NO a slower FIG:2 THE MESH OBJECT OF CATALYTICreaction also goes on, which is CONVERTER4NH3 +6NO→5N2+6H2O.--------------------------(2)When the NO2/NO ratio is close to unity,a muchhigher rate reaction prevails, often known as „fastSCR‟ 2NH3+NO+NO2→2N2+3H2O.--------------------(3) Madia et al performed an investigation ofthe side reactions observed during the SCRprocess.Madia et al also investigated the effect ofthe increased NO2 fraction caused by an oxidationcatalyst located upstream of the SCR converter, andconcluded that increasing the NO2/NO fraction upto 1 enhances NOx conversion at low temperatures,due to the reaction with NO and NO2,which issignificantly faster than reaction with NO andO2.In the numerical studies ,heterogeneousreactions mechanisms are used to describe surface FIG:3 INLETreactions on catalytic plates,where the chemicalspecies are absorbed,react with the surface plane ofthe catalyst,followed by the desorption. The stationary plug flow is used In thesimulation process, and the study 1 is computed toplot the graphs according to different temperatures. 400 | P a g e
  3. 3. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408FIG:4 OUTLET FIG:7 SUPPORTING WALLSFIG:5 INLET WALLS FIG:8 REACTION SURFACE 2.1 NO Reduction in a Monolithic Reactor This is a modelling example of catalytic converter that removes nitrogen oxide from a car exhaust through the addition of ammonia. This example shows an application of the above described modelling strategy and demonstrates through a series of simulations how an understanding of this reactor and its system can be improved. To do this, it uses a number of the interfaces and features found in the Chemical Reaction Engineering Module. This example illustrates the modelling of selectiveFIG:6 OUTLET WALLS reduction of nitrogen oxide (NO) by a monolithic reactor in the exhaust system of an automobile. Exhaust gases from the engine pass through the channels of a monolithitic reactor filled with a porous catalyst, and by adding ammonia (NH3) to this stream, the nitrogen monoxide can be selectively removed through a reduction reaction. Yet, ammonia (NH3) is also oxidised in a parallel reaction, and the rates of the two reactions are affected temperature as well as composition .This 401 | P a g e
  4. 4. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408means that the amount of added ammonia must temperature. From a mass transfer point of view,exceed the expected amount of nitrogen oxide channels of the reactor monolith can be consideredwhile not being so excessive as to release NH3 to to be uncoupled to one another. Therefore it isthe atmosphere. reasonable to perform initial simulations where aThe simulations are aimed at finding the optimal single reactive channel, modelled by nonisothermaldosing of NH3, and investigating some of the other plug flow equations represents the monolithoperating parameters in order to gauge their effects. reactor. This model is set up and solved using theOn defining the modelling strategy, first the Reaction Engineering interface.selectivity aspects of the kinetics are studied mymodelling initial reaction rates as function of 2.4 MODEL EQUATIONtemperature and relative reactant amounts. Assuming steady state, the mass balanceInformation from these studies point to the general equation for a flow reactor is given byconditions required to attain the desired selectivity. 𝐝𝐅𝐢 = 𝐑𝐢The reactor is then simplified and modelled as a 𝐝𝐕 Where F is the species molar flow rate (mol/s) ,Vnon-isothermal plug flow reactor. This reveals the represents the reactor volume(m2)and is R, thenecessary (NH3) dosing levels based on the species net reaction rate (mol/(m2s)).the energyworking condition of catalytic converter and balance for the ideal reacting gas is:assumed flow rate of NO in the exhaust stream. A 𝑑𝑇3D model of catalytic converter is then set up and 𝑖 𝐹𝑖 𝐶 𝑝,𝑖 . = 𝑄 𝑒𝑥𝑡 + 𝑄---------------------------- 𝑑𝑉solved. This includes mass transfer, heat transport, -----(5)and fluid flow and provides insight and information Where CP is the species molar heat capacityfor optimizing the dosing levels and other (J/mol.k) and Qaxt is heat added to the system peroperational parameters. unit volume (J/m2s). Q denotes the heat due to chemical reaction (J/(m2s)).2.2 CHEMISTRY Q= - j Hj rj Two parallel reactions occur in the Where h, the heat of reaction (j/mol) and, r thezeolite/kaolin washcoat of the monolithic reactor reaction rate (mol/m3s).The desired reaction is NO reduction by ammonia: The reactor equations are solved for a channel 0.36 4NO + 4NH3 + O2 → 4N2 +6H2O-------------- m in length with a cross section area of 12.6 mm2 --------------(1) .It is assumed that that exhaust gas containing 41.1 mmol/m3 of NO at a temperature of 523K However, ammonia can at the same time undergo passes through the channel at 0.3m/soxidation: 4NH3 + 3O2 → 2N2 + 6H2O---------------------- 2.5 THE 3D REACTOR--------(2) It is clear from the kinetic analysis as wellThe heterogeneous catalytic conversion of NO to as from the single channel model that temperatureN2 is described by an Eley-Rideal mechanism .A plays a central role in affecting the optimal dosingkey reaction step involves the reaction of gas phase of NH3.As the temperature distribution is likely toNO with surface adsorbed NH3.The following rate vary from the channel to channel in a catalyticequation (mol/(m3s)) has been suggested in Ref.1 converter, a full 3D reactor model is called for.for Equatiion1: r1=k1 cNO( acNH3/1+ acNH3)------------------------------ 2.6 Model geometry----(3) The monolithic reactor has a modular Where structure made up of monolith channel blocks and E1 k1=A1exp(− ) supporting solid walls. The reactor is 470 mm long RgT And and 50 mm in radius. Eo a=A0 exp (− ) RgT For Equation2, the reaction rate (mol/(m3s)) is given by r2=k2cNH3----------------------------------------------------(4) Where E2 k2=A2 exp (− ) RgT Fig:9 NO reduction chemistry takes place in the2.3 THE PLUG FLOW REACTOR channel blocks. Supporting walls hold together the To find the minimum level of (NH3) full reactor surface.required to reduce the NO present in the exhaustgas requires a reactor model accounting forchanging reactant concentrations and system 402 | P a g e
  5. 5. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-4082.7 MODEL EQUATIONS AND channel models are connection though the heat -ASSUMPTIONS transfer equation for the reaction monolith. In the present example a pseudohomogeneous approach is used to model the 2.9 Fluid Flowhundreds of channels present in the monolith Assuming fully developed laminar flow inreactor. As no mass is exchanged between channels, the average flow field is proportional tochannels, each channel is described by 1D mass pressure difference across the reaction .The flow oftransport equations. Furthermore, fully developed reaction gas through the monolith can the belaminar flow in the channels is assumed, such that modelled using a Darcy‟s law interface withthe average flow field is proportional to the following governing equation;pressure difference across the reactor. The fluid 𝛻. (𝑝 𝑢)=0flow transports mass and energy only in the 𝑘 u=- 𝛻𝑝channel direction. The energy equation describes µthe temperature of the reacting gas in the channels, The monolith is treated as a porous matrix with theas well as the conductive heat transfer in the effective permeability k(m2).the densitymonolith structure and the supporting walls. As the ,p(kg/m3),and viscosity,µ(Pa.s),represent propertiestemperature affects not only the reaction kinetics of the reacting gas.but also the density and viscosity of the reactinggas, the energy equation is what really connects the 2.10 Heat Transferchannels in the reactor structure turning this into a A single temperature equation describing the heat3D model. transfer in porous monolith reactor can be written as: 𝜕𝑇2.8 Mass Transport (pCp)eq +pf Cpf u𝛻𝑇 = 𝛻.(keq 𝛻𝑇)+Q---------------- 𝜕𝑡 The mass balance describing transport and -(7)reaction in reacting channels are given by For the stationary case this reduces to:diffusion-convection equations at steady state: piCpfu.𝛻𝑇=𝛻.(keq 𝛻𝑇)+Q-------------------------------- ∇. (−Di∇ci)+u.∇ci = Ri------------------------------ --(8)--------(6) Where pi(kg/m3) is the fluid density Cp(J/kg.K) isHere Di denotes the diffusion coefficient (m2/s), CI The fluid heat capacity ,and keq (W/(m.k))is theis the species concentration (mol/m3), and u equals equivalent thermal conductivity. Furthermorethe velocity (m/s). The term R (mol/(m3s)) u(m/s) is the fluid velocity field, which in thiscorresponds to the species rate expression. model is calculated in the Darcy‟s law interface,Mass transport is only allowed in the direction of and Q(W/m3) is the heat source, which is due tothe channels, corresponding to direction of the x- exothermic chemical reaction:axis in the 3D geometry used in this example. For Q= Q1 + Q2 =-r1H1-r2H2the diffusive transport this is accomplished by The equivalent conductivity of the solid –fluidsetting the y and x components of the diffusivity system, keq is related to the conductivity of thematrix to zero. The pressure –driven flow in the solid keq, and to the conductive of the fluid, keq by:monolith is also defined in the direction of the x- Keq=ʘP kp+ ʘf kfaxis hereby restriction the convective mass Here ʘp denotes the solid materials volumetransport to the channel direction as well. Each friction, here 0.25, which is related to the volumemonolith channel thus behaves as a 1D plug-flow fraction of the fluid ʘfby:model with included diffusion. These separates ʘf+ʘp=1 model (equation8). the chemical reactionEquation (8) is the equation set up by heat transfer engineering module uses the following setinterface for a fluid domain. For the supporting in polynomial as default expressions describingthe reactor, only heat transfer by conduction species thermodynamics propertiesapplies: Cp, i =Rg (a1+a2T+a3T2+a4T3+a5T4) --------------------− 𝛻 (k8 𝛻𝑇)=0 ----------------(9)Where k8 (w/m-k) is the thermal conductivity for hi = Rgthe solid walls a 2T 2 a3T 3 a 4T 4 a5T 5As mentioned, the temperature affects not only ( a1T      a 6)reaction kinetics but also the density and viscosity 2 3 4 5of the reacting gas. In this way the heat transfer ----(10)equation connects channels in the reactor structure. si = Rg (a1InT+a2T 2 3 a3T a 4T    a5   a 7) 42.11 Thermodynamic and transport Properties -------- 2 3 4 Accurate thermodynamic data is requiredas input to energy balance equation, both in the -(11)plug flow model (equation5) and the 3Dmonolith 403 | P a g e
  6. 6. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408Here Cp ,denotes the species heat capacity (J/mol The chemical Reactions are modelled withk),T the temperature (K) and Ri the ideal gas chemical kinetic reaction mechanism. It is used toconstant ,8.314 (j/mol k) further ,h is the molar perform three different analyses concerning theenthalpy (j/mol) and SI represent its molar entropy reduction of NO in a monolithic reactor. the(J/mol k).A set of seven coefficients per input for reactions modelled are:the polynomials. The coefficients a1 through a2 1) Kinetic Analyses-to explore the system ofrelate to the species heat capacity ,the coefficient a3 competing reactions and learn whatis associated with the species enthalpy of formation conditions that promote selectivity(at 0 K) and the coefficient a1 comes from the towards NO reductionspecies entropy of formation (at 0 K). 2) Plug Flow Reactor Model- to explore theThe equation from outline by equqtion9 through coupled mass and energy balanceequqtion11 is referred to as CHEMKIN or NASA equations in a single channel model,format (ref 2) Database resources list the needed resulting in a first estimate of the NH3coefficients are for different temperature intervals dosing level(ref3).in the this exampl. 3) 3D Reactor Model-testing the reactor3 RESULT AND DISCUSSIONS operating conditions in a full 3D reactor To model the injection of urea a typical representation, noting the space-dependentcatalytic converter is chosen whose dimension is effect due to coupling between monolith100 mm and length is 470 mm. It is necessary to channels.inject urea as a liquid solution (called Ad blue The surface reaction of NOx reduction will besolution) into the hot exhaust gas, which is effective only at certain temperatures. Hence tonormally between the temperatures of 423k to573k find out the range at which the reactions aredepending upon the load of the engine. effective, the simulations were conducted for fourUrea injection process is modelled by Ad blue exits. The temperature profile came acrossliquids (32.5% urea and 73.5%water), solid model corresponding the temperatures 423k, 523k,is created and meshed in comsol multiphysics4.2 623k,&723k with the changes in molar flow ratesoftware. and temperatures. The results are plotted below3.1 SIMULATION PROCEDURE The graphs of molar flow rate are plotted below: For reacting gas mixtures the reactionengineering feature makes use of kinetic gas theoryto set up expressions for transport properties suchas diffusivities viscosity and thermal conductivityas function of temp ,pressure and composition .inthis example ,the species diffusivities (m3/ s) arecalculated using the formulaD  2.695.10 3 . T3 M A   M B  / 2.10 3 M A M B  P  A B  D---------(12) (a) Exhaust gas temperature 423kWhere 𝛺 D is a collision integral     D  f T ,  ,  ,    kb  404 | P a g e
  7. 7. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408 length of the catalytic converter.Fig:10 show the comparison of flow rates of ammonia and nitrogen oxide (NO) along the length wise direction. It is evident from the picture that, as the temperature of exhaust increases the reduction of NO is enhanced. For example at a volume of 15 units the NO level are147.5 and 2.0 moles /sec for the temperatures of 423k and 523k.Further increase in temperature does not enhance NO reduction as it can be seen for the figures 10 (b) and 10 (c).Analysing the figure it can be seen that the NO level is around 2.5 moles/sec. at a location of 15 volume units. Hence it can be concluded that the optimum b)Exhaust gas temperature 523k exhaust gas temperature for the NO reduction with ammonia for the given NO emission level is 523k. The graphs of temperature profile are given below; c)Exhaust gas temperature 623k (a) Exhaust gas temperature 423k d) Exhaust temperature 723kFig:10 Spatial variation of flow rates of NH3 andNO for different temperatures with respect tovolume of catalytic converter.Various parameters like the reaction rates of b)Exhaust gas temperature 523kreaction 1 and reaction 2, molar flow rates andtemperature across the domain were calculated andmeasured. The measurements were done across the 405 | P a g e
  8. 8. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408 apparently NO reaction induced temperature rise. The Fig: 11 b) temperature 523k represents that the temperature is 523 k at the zero unit volume of the SCR system and it suddenly goes high up to 530k at 10 unit of volume of the SCR system and then continuously decreases to below 490k at the outlet of SCR system. From the Fig:11 c)temperature 623k , it shows that the temperature graph rapidly increases from 623k temperature to above 650k temperature within 2 unit volume of the SCR system and then decreases to below 560k to the outlet of SCR system. The last Fig: 11 d) temperature 723k represents the temperature increasement from 723k to above 750k very fastly within the single unit volume of the SCR system and then continuously decreases to below 620k temperature at the outlet of the SCR system. c)Exhaust gas temperature 623k Ammonia (NH3) and nitrogen oxide (NO) for the surface concentration. From the fig:12 concentration figure of NO & NH3, d) Exhaust temperature 723k it is shown that the surface concentration (mol/m3) is maximum at inlet of the model, continuously decreasing towards the outlet of the model. ThisFig: 11 Spatial variation of exhaust gas temperature represents that the pollutants like NO,NH3 are highfor different exhaust conditions (inlet SCR in concentration at the inlet of the catalytic modelcondition). and while passing through the catalytic core the pollutants get converted to some other elements by From the fig: 11 a) temperature 423k,it shows the chemical reaction inside the catalytic core. that the temperature is very high (about 423k) at Which shows the lower concentration value of NO the zero volume (inlet) level of the SCR system, & NH3 at the outlet of the model. and it continuously reduces to about 402 k at the outlet of SCR system. It shows that there is12 a. Concentration of NO 12 b.concentration of NH3Fig: 12 Surface concentrations of NO & NH3 for atypical 3D volumeAmmonia (NH3) and nitrogen oxide (NO) forthe slice concentration. 406 | P a g e
  9. 9. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408 Contour Plots of NH3 & NO 13 a concentration of NO 13 b. 15 a Contour Plots of NH3 15 b concentration of NH3 Contour Plots of NO Fig: 13 slice concentration of NO & NH3 for a Fig 15 Contour Plots of NH3 & NOtypical 3D volume Contour plots of both the NH 3 and NO is higher at inlet and reduced to almost zero at the exit. Moreover the ammonia slippage is minimum in thisThe above figures shown the slice concentration case. Hence we can safely assume that health(mol/m3) of NO and NH3 which is maximum at hazard due to ammonia is nil.inlet and continuously decreasing towards the Enthalpy of reaction 1 & reaction 2outlet. It refers the slice concentrations of NO &NH3 part by part how & by what value it isdecreasing towards the outlet of the model. Itrepresents that the surface reaction takes place fromthe inlet of the model and it is well finished beforethe outlet of the model.Pressure on both the cases of slice and surface ofthe catalytic converter 16 a Enthalpy of reaction 1 16 b Enthalpy of reaction 2 Fig 16 Enthalpy of reaction 1 and reaction 2 The Fig: 16, shows that the enthalpy is higher at the inlet portion and decreases to the outlet of the SCR system of both the cases of Reaction 1 & Reaction 2.This shows that by the time the exhaust stream enters the middle of the Catalytic core 13 a Slice pressure almost all the reactions have been completed. At 14 b surface pressure the exit no reaction occurs at all. Reaction rate of reaction 1 & reaction 2 Fig 14 Slice and Surface Pressure of Catalytic Converter model.The figures show the pressure distribution throughthe catalytic converter model, which is having ahigher pressure at the inlet and continuouslydecreasing pressure towards the outlet for both theslice and surface cases. This represents that at theinlet of the model due to the injected ad bluesolution and entering exhaust gas from the enginethe pressure is high, as the reaction takes place atthe entrance of the catalytic core, the specificvolume increases and hence the pressure increases.As the gas flows further downstream the reactiontemperature reduces and hence the pressure toodecreases. 407 | P a g e
  10. 10. B. Jothithirumal, Dr .E. James Gunasekaran, Chandan Dey / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.399-408 17 a. reaction rate of reaction 1 17 b. system. The reaction rate pictures of reaction 1 andreaction rate of reaction 2 reaction 2 also shows that the reaction rate is high Fig 17 Reaction rates of reaction 1 and at the inlet and decreases at the out let of the SCRreaction 2 system.The Fig: 17 (A) shows that the reaction rate of The concentration of NOx and NH3 is alsoreaction 1 is higher at the inlet of SCR system and maximum in the inlet and reduced downstream ofcontinuously decreases to the outlet of the SCR the SCR system .The pollutants like NO and NH 3system. The Fig: 6.6 (B) shows that the reaction are higher in concentration (0.0557 mol/m3) .Therate of reaction 2 is also much higher at the inlet of concentration of NO is reduced to a lowest value ofSCR system and continuously decreases to the flow at 0.005 mol/m3 at the exit of the catalyticoutlet of the SCR system. This represents that the core. Whereas the NH3 concentration at exit ischemical reaction started from the inlet of the SCR around 0.01 mol/m3.This clearly shows that thesystem and it is well finished before the outlet of surface reaction occurs satisfactorily at the catalyticthe SCR system. The reaction is completed within core.the catalytic core. Moreover it can be concluded that at 523k temperature the catalytic converter is highlySurface temperature effective and it reduces the pollutants to a very minimum level. 5. REFERENCE 1. B.Jothi Thirumal and Dr. E.James Gunasekaran, “Numerical Study on Ammonia Evaporation for Urea Selective Catalytic Reduction System”International Journal of Science and Advanced Technology (ISSN 2221- 8386) Volume 1 No 5 July 2011. 2. S.Pietrzyk, F.Dhainaut,A.Khodakov and P.Granger, „Catalytic Reduction under Surface temperature unsteady- state conditions. Modelling with COMSOL’ Excerpt from the proceedings of the COMSOL users Fig18. Surface temperature of the catalytic conference 2006 Paris.model 3. K. Hirata,N Masaki,M Yano,H The surface temperature figure shows that the Akagawa,K, Takada, J kusaka,and T Mori,temperature variation is maximum at the inlet of “Development of an improved ureathe model which is approximately 523k and it selective catalytic reduction-dieseldecreases to the outlet where it seems to be less particulate filter system for heavy-dutythan 440k.This represents that the reaction has been commercial vehicles” Int.J.Engineoccurred from the inlet of the SCR system and it is Res.vol.10 on 15 May 2009.completed before the exit of the SCR system. 4. D Tsinoglou and G Koltsakis, “Modelling of the selective catalytic NOx reduction4. CONCLUSION in diesel exhaust including ammonia The SCR technology is a successful storage” Proc.IMechE Vol.221 Part D:method of reducing the harmful gases such as NOx, J.Automobile Engineering on 13 SepHC, CO. The aim of the research work is to show 2006.the reaction of NO and NH3 in the monolith reactor 5. S-C Jung and W-S Yoon, “Modelling andof catalytic converter with varying temperatures by parametric investigation of NOxusing COMSOL MULTIPHYSICS 4.2 software. reduction by oxidation precatalyst-From the simulation study it was observed that the assisted ammonia-selected catalyticconversion of NO into N2 is effective only in the reduction” Proc.IMeche Vol.223 part D:middle range of temperature i.e. about 523k. J.Automobile Engineering on 15 mayFrom the enthalpy picture it is seen that the internal 2009.energy is maximum at the inlet of the SCR systemand decreases towards the outlet. This representsthat the reaction is started from the inlet of SCRand finished well before the outlet of the SCR 408 | P a g e