Research On The Influence Of Syngas Direct Injection On Engine Combustion And Particulate Characteristics Based On Combined Injection Mode

With increasing vehicle holdings,the particulate issue from GDI vehicles becomes more and more serious.From the point of environmental conservation and emission regulations,reducing the particulate number(PN)should be a matter of instant importance.This paper adopts syngas direct injection combined with combined injection mode to reduce engine particulate emissions as much as possible.Plenty of bench tests have been conducted to analyze engine combustion and particulate characteristics.During the whole experiments,three injection modes have been directly compared within the same construction,which are gasoline direct injection(GDI),gasoline port injection combined with gasoline direct injection(PGDI)and gasoline port injection combined with syngas direct injection(PSDI).From the direct comparison on engine combustion and particulate characteristics,the specific influences of these two technical methods have been concluded.And the potential and actual value of syngas direct injection combined with combined injection mode has been analyzed.Firstly,the combustion characteristics and common gaseous emissions of engine have been researched.During the research,excess air ratio,ignition timing and direct injection pressure have been chosen as main parameters,while the whole experiments use single variable method.This part includes the influence of syngas direct injection combined with combined injection mode on cylinder combustion state,engine dynamic performance,engine cyclic variations and common gaseous emissions.Among them,cylinder combustion state can be used as the theoretical basis of particulate characteristics.Then,analyzing the influence of syngas direct injection combined with combined injection mode on engine particulate characteristics under the same experimental points.This section has two main parts,the first part aims on the total particle number,while the second part analyzes the influence of controlling parameters on specific particle size distribution.To broaden the researching scope and conclude the comprehensive influence of syngas direct injection combined with combined injection mode,researching on different operating points and different fuel distribution ratios have been conducted in follow-up studies.Analyzing engine combustion and particulate characteristics through a large number of bench tests,sensitivities of different injection mode on controlling parameters can be obtained,which is useful to formulate an efficient and reasonable strategy to reduce engine particulate emissions.These main conclusions have been achieved through the research:1.Engine uses PSDI mode can obviously accelerate the combustion speed,which also raises the peak cylinder pressure,the peak heat release rate and the peak cylinder temperature,while the peak corresponding times are the earliest.Within the PSDI mode,engine has the best dynamic performance,the least cyclic variations and the largest thermal efficiency,while the potentiation becomes more obvious under leaner situation.2.PSDI mode brings very low CO emission and unburned HC emission,while they are insensitive with controlling parameters.As PSDI mode has the highest cylinder temperature,it has the highest NOX emission.The syngas direct injection obviously enhances the combustion stability and lean burn performance,so large EGR ratios and lean combustion technology can be used to reduce NOX emission.3.The total particulate number of GDI mode and PGDI mode show a downward trend with higher excess air ratios,when ignition timing is fixed at 15° CA BTDC.Total particulate number of PSDI mode decreases with higher excess air ratios under small load.However,total particulate number of PSDI mode first increases then decreases with higher excess air ratios under high load,while the total number maximizes at ? =1.4.4.Three different injection modes show different trends with advancing ignition timings.The total particulate number of GDI mode first decreases then increases with advancing ignition timings,which minimizes at MBT point.The total particulate number of PGDI mode shows little change with different ignition timings.The total particulate number of PSDI mode first increase then decreases with advancing ignition timings,which maximizes at MBT point.5.The particulate number decreases with higher direct injection timings.When PSDI mode select 5 MPa injection pressure,the total particulate number is already very low which obviously less than GDI mode and PGDI mode(even adopts 7 MPa injection pressure).So the requirement of PSDI mode is much lower,and less injection pressure can obviously reduce particulate number.6.PSDI mode can dramatically reduce engine particulate emissions under low and medium load,while the reduction declines under high load,which even appears higher total number than PGDI mode in some special points.To reduce engine particulate emissions as much as possible,PSDI mode should be used in low and medium load,while PGDI mode should be used in high load.7.When the excess air ratio is relatively small,changing fuel distribution ratios can effectively reduce engine particulate emissions.When the excess air ratio is relatively high,changing fuel distribution ratios only has little influence on engine particulate emissions.