| The global focus on reducing pollutant emissions from automobiles has intensified in recent years.Enhancing in-cylinder combustion and mitigating engine pollutant emissions have become crucial objectives,prompting advancements in fuel injection technology,and integrated aftertreatment systems.Within the integrated control system of the engine,post-injection assumes a pivotal role in optimizing both combustion and emission performance.This in-cylinder injection technique proves instrumental in reducing harmful engine emissions while preserving engine efficiency,often without the need for exhaust after-treatment devices.Notably,post-injection generates additional heat,elevating in-cylinder temperatures.This,in turn,fosters the formation of OH radicals and light hydrocarbons(HCs)through the thermal cracking of diesel fuel,thereby facilitating the oxidation process of soot.Post-injection proves versatile not only in reducing emissions but also in generating reactive light hydrocarbons(HCs),which serve as valuable heat sources in the oxidation catalytic converter.This strategic use of post-injection plays a pivotal role in maintaining optimal temperatures for the regeneration of the Diesel Particulate Filter(DPF).Elevating exhaust gas temperature and introducing reactive light HC reactants through in-cylinder post-injection represent effective measures to support the efficient operation of diesel engine exhaust after-treatment systems for pollution control.The study encompasses a series of experiments and numerical simulations aimed at evaluating the impact of varied post-injection strategies on engine combustion and emissions.Leveraging the geometric features of the engine combustion chamber,the CONVERGE CFD software facilitated the creation of a simulation model for a 1/8-scale diesel engine operating at a constant speed of 1200 r/min.This comprehensive approach included a brief overview of turbulence,combustion reaction,and NOx emission models.The simulation results underwent rigorous comparison with experimental data,confirming the model’s validity.The CFD simulation results demonstrated a commendable alignment with experimentally collected data.The investigation delved into the analysis of post-injection parameters,shedding light on their influence on combustion behavior and pollutant formation.This detailed exploration serves as a foundational step toward a deeper understanding of post-injection mechanisms and the optimization of postinjection strategies,outlining the primary focus of this research endeavor.(1)The impact of post-injection parameters on engine performance at a constant speed of1200 revolutions per minute(r/min)was systematically assessed through both experimental and computational evaluations.This comprehensive analysis considered the effects of post-injection parameters on crucial indicators such as indicated instantaneous heat release rate(IHRR),incylinder pressure,in-cylinder temperature,as well as regulated and unregulated emission characteristics.In the bench test experiment,the post-injection timing(SOI)was varied between20-120 °CA ATDC,with post-injection mass(PIM)ranging from 5-15 mg.Results underscored the efficacy of post-injection technology in significantly reducing both regulated and unregulated emissions when compared to a single main injection.Notably,a trade-off relationship between soot and NOx emissions was observed under different post-injection conditions.Specifically,at an SOI of 40 °CA,soot emissions were reduced by up to 26% in comparison to a single main injection.Early SOI conditions resulted in lower unregulated emissions(excluding formaldehyde and acetaldehyde).Furthermore,at an SOI of 20 °CA and a post-fuel injection mass of 15 mg,NOx emissions witnessed a 20% reduction,while total hydrocarbons(THC)emissions experienced a notable 60% decrease compared to a single main injection.(2)The investigation into the impact of post-injection parameters on combustion and emission characteristics extended to different engine load conditions while maintaining a constant engine speed.Experimental analyses were conducted at three distinct engine loads 20%,40%,and 60%,corresponding to average effective pressures of 0.5 MPa,1.15 MPa,and 1.65 MPa,respectively.Notably,results revealed that NOx,THC,and soot emissions were most pronounced with postinjection under higher(60%)load conditions in comparison to a single main injection.Conversely,the concentration of unregulated emissions was minimal at the 20% load condition.Significantly,post-injection technology demonstrated effective emission reduction,particularly at lower engine loads.Earlier Start of Injection(SOI)consistently augmented engine output power and exhaust temperature across all engine operating conditions.Specifically,at medium(40%)and high(60%)loads,an SOI of 60 °CA resulted in a noteworthy reduction in NOx emissions(up to 25%),soot emissions(up to 40%),CO emissions(up to 12%),and THC emissions(up to 60%).Additionally,an increase in the detection of light hydrocarbon(HC)compounds was observed,presenting potential benefits for after-treatment devices.(3)The impact of post-injection parameters on emission performance was systematically examined under varied engine speeds while maintaining a constant engine load.Three distinct speeds 1000 r/min,1200 r/min,and 1400 r/min were selected to investigate their influence on postinjection efficiency and engine emissions.Results underscored that,in comparison to higher engine speeds,implementing the post-injection strategy at a lower speed(1000 r/min)notably enhanced combustion characteristics,including IHRR,in-cylinder temperature,and pressure.However,this improvement was accompanied by a significant increase in emissions.Conversely,at 1400 r/min,an earlier SOI and increased post-injection fuel mass effectively reduced emissions of NOx,CO,and Non-Methane Hydrocarbons(NMHC).Soot emissions exhibited an initial rise followed by a decline with delayed SOI.Notably,at the higher engine speed of 1400 r/min,post-injection demonstrated a substantial reduction in soot emissions compared to the other two speeds.Additionally,at 1400 r/min,post-injection played a mitigating role in the formation of reactive light hydrocarbons such as C3H8,C3H6,and C2H4 under different PIM conditions.(4)Given the pivotal role that light hydrocarbon(HC)compounds play in enhancing the efficacy of Diesel Oxidation Catalysts(DOC)to reduce emissions and facilitate Diesel Particulate Filter(DPF)regeneration,this research delved into assessing the impact of various post-injection strategies on exhaust HC compound emissions.The primary focus was on understanding how different post-injection parameters influence HC species formation and distribution under varying temperatures.The SOI was varied within the range of 20-120 oCA,and the post-injection fuel volumes were set at 5 mg,10 mg,and 15 mg,respectively.Results unequivocally demonstrated that post-injection parameters significantly influence the composition and formation of HCs in diesel engine exhaust.Under SOI conditions of 20-40 °CA,light HCs experienced a reduction due to higher in-cylinder temperatures and the maximum oxidation of post-injected fuel.Additionally,an increase in post-injection fuel quantity promoted the formation of more light HCs through cracking.At an SOI of 60 °CA with post-injection fuel volumes ranging from 5-15 mg,peak values of C1,C2,and C3 compounds were observed,with Non-Methane Hydrocarbon(NMHC)emissions reaching their peak under an SOI of 80°CA.During early SOI(20-40 °CA)with post-injected fuel ranging from 5-15 mg,the concentration of light HCs constituted approximately 50-80% of Total Hydrocarbons(THC)emissions.Conversely,with delayed SOI(80-120 °CA),the proportion of the C8 compound surpassed that of all other measured HC compounds.Notably,post-injection proved effective in producing lighter HCs at SOI intervals of 60~80 °CA,demonstrating potential benefits for post-treatment devices such as DOC,Lean NOx Trap(LNT),and DPF. |
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