Generation of Reactive Chemical Species/Radicals through Pilot Fuel Injection in Negative Valve Overlap and Its Effects on Engine Performances 2022-01-1002

This study investigated the potential of generating reactive chemical species (including radicals) through pilot fuel injection in negative valve overlap for improving the combustion and emissions performances of spark ignition gasoline engines under low load and low speed operating conditions. Several Ford sub-models were used for simulating the physics and chemistry processes of injecting a small amount of fuel in NVO (negative valve overlap). Effects of different NVO degrees and different pilot injection timings, factors for fuel conversion were simulated and investigated. CO and H₂ conversions during NVO, CO and H₂ amounts before spark timing were used for comparing different schemes. Finally, effects of pilot injection during NVO on engine performances were studied, including in-cylinder pressure, in-cylinder burn rate, in-cylinder NOx and UHC (unburned hydrocarbon), IMEP (indicated mean effective pressure), PMEP (pumping mean effective pressure), and ISFC (indicated specific fuel consumption). Based on simulation results and analyses, several conclusions were drawn: significant amount of reactive chemical radicals or species can be generated during NVO; the larger the NVO degree, the more conversion of CO and H₂; the earlier the pilot fuel injection timing, the more the conversion of CO and H₂; more O₂ favors the conversion rate of CO and H₂; due to reactive CO and H₂, burn rate is fast; at low load, high EGR can be used, causing lower NOx emission, while the UHC, IMEP, and ISFC can keep the same level as the baseline engine case.