Numerical Analysis And Algorithm Investigation Of Diesel Particulate Filter Fuel Injection Regeneration System

With the rapid development of automobile industry,diesel engine is widely used worldwide.Compared to its gasoline counterpart,diesel engine has advantages of high torque,superior fuel economy,low unburned hydrocarbon emission and so on.However,particle matter emission of diesel engine is much higher than gasoline due to diesel properties and ignition method.Particulate matter is one of the main inducements of atmospheric haze and respiratory diseases.To reduce emission of particulate matter,some in-cylinder purification technologies are adopted such as electronically controlled common rail injection and intake turbo-charging.With increasingly stringent emissions regulations(National VI,Europe VI and TIRE2)to restrict both particulate mass and number,after-treatment technologies are indispensible,among which diesel particulate filter(DPF)is the most efficient device.Regarding to thermal regeneration system of DPF,fuel is injected at front end of diesel oxidation catalyst(DOC)to raise temperature of exhaust gas and further burn deposited particulate inside DPF.Through numerical simulation,combustion characteristics of diesel and other common gas fuels in DOC micro-channel are investigated.Transient process of soot combustion in DPF is researched as well.Raising reliable modeling methods,coupled algorithom,estimation algorithm of particulate loading and reasonable control strategies are meaningful to design fuel injection regeneration system both theoretically and in real application.Firstly,the computation fluid dynamics(CFD)model of diesel surrogate n-dodecane(n-C₁₂H₂₆)catalytic combustion in micro-channel was developed.Detailed gas phase and hierarchical surface mechanisms were utilized.In specific,methane which is the simplest carbon-contained product of n-dodecane decomposition reacts on platinum active sites following elementary surface mechanism.The other complicated carbon-contained products react with rate defined by surface molecular dynamics theory and the generated absorbed-state carbon,hydrogen and oxygen atoms react following elementary surface mechanism.Accuracy model was verified with experiment and combustion characteristics of some other common fuels like hydrogen,methane and propane were compared.Computation results revealed that n-dodecane has relatively wider stability envelope under low inlet velocity and narrower stability envelop under high inlet velocity.Meanwhile,n-dodecane yields smaller wall temperature gradient under high inlet velocity.However,emission is an issue.This part of work provides theoretical guidance on catalytic combustion modeling of complicated fuels.Secondly,a porous wash-coat resolved CFD model of methane catalytic combustion in micro-channel was developed.Molecular and effective mass transport model was adopted in pure fluid domain and porous wash-coat domain,respectively.The interplay of homogeneous reactions(HR)and heterogeneous reactions(HTR)under different channel confinements were discussed with the built model.Internal diffusion limitation and overall catalyst usage were analyzed quantitatively.Effects of porous layer properties including porosity,average pore diameter and tortuosity were investigated.The numerical model predicted velocity,species distribution and influence rules of porous layer properties accurately.This part of work completes modeling work of catalytic combustion in micro-channel.Meanwhile,it's instructive to catalyst manufacturing and selection.During DPF regeneration,thickness of soot cake layer decreases due to soot consumption.Normally,dynamic mesh is incapable of simulating non-uniform computation domain variation.Thus,compaction algorithm of porous computation domain is developed and applied to modeling work of DPF regeneration.At the end of every time step,local soot concentration is exchanged between adjacent cells based on porosity criteria.By doing this,collapse is simulated in the process of soot cake combustion.Results show that numerical model coupled with compaction algorithm can predicts temperature and soot concentration profiles precisely and varying soot catalytic reactivity leads to different regeneration modes.This section provides new method in modeling DPF regeneration.Considering the fact that maximum temperature,temperature increasing rate and regeneration timing are largely depend on soot loading amount,an algorithm of soot loading prediction is built.The algorithm includes Peclet number determination and properties of soot cake layer calculation.This algorithm is helpful in deciding regeneration timing,prolonging DPF lifetime and lowering fuel consuming.Ultimately,control strategies of DPF regeneration system were raised.It includes MAP update of regeneration termination,timing determination,real-time diagnosis and termination determination.Unburned ash effect was considered to update inlet channel geometry,which is instructive in industrial application.