Research On Fuel Injection Strategy And Combustion Optimization For Methanol/PODEn Engine Under Premix Compression Combustion Ignition Mode

With the soaring number of cars in our country,the energy crisis and environmental pollution have been aggravated,which put forward higher requirements for the innovation of internal combustion engine.In this thesis,the combustion mode of Premix Controlled Compression Ignition(PCCI)is chosen: the clean fuel methanol premixed with air,is injected into the intake port,then the PODEn is injected directly into the cylinder,the premixed gas is ignited by PODEn’s spontaneous combustion,thus realizing highly efficient and clean combustion.Particularly,intake parameters and fuel injection strategy are the key factors that affect the mixture degree and combustion quality of fuel and air.the effects of initial conditions and fuel injection strategy on the combustion characteristics of a low-load methanol/PODEn hybrid fuel combustion model were researched under the module of PCCI by the simulator CONVERGE.The effects of different methanol equivalence ratio,intake air temperature and intake air pressure on the combustion and emission of methanol/PODEn mixed fuel engine were studied,analyzed and optimized by the law curve,equivalence ratio and temperature distribution cloud of the combustion characteristic index.The results show that where the proportion of methanol is appropriately increased,the high cetane number of the homogeneous mixture in the cylinder decreases,the combustion activity is reduced,the ignition start point is delayed,the overhigh combustion rate is improved under low-load conditions,the fuel utilization rate is improved,and the emission of Soot and NOx is lower.Especially the 35% of methanol equivalence ratio performs the best,because the higher temperature and pressure of the intake air promotes the diffusion movement of molecules,stimulates the collision between molecules,and improves the ignition combustion characteristics and combustion efficiency,but high temperature and the oxygen enrichment promote NOx production.In order to further optimize the combustion emission characteristics of methanol/PODEn dual fuel,the proportion of methanol in M35 was selected to study the influence of different injection strategies on the combustion characteristics,mainly including single injection timings,pre-injection timings(SOI1)of two injections and main-injection timings(SOI2)of two injections.In the single injection strategy,advancing injection helps to form a homogeneous mixture of dual fuel in advance,advances the ignition phase,shorten the combustion duration period,concentrate the heat release,greatly reduces NOx,HC,and Soot.And where the fuel injection time is22°CA BTDC,the reaction between fuel and mixture is mild,and the emission control is balanced.The injection ratio and the fuel injection duration determine the influence of SOI1 and SOI2 on the combustion characteristics.Where the pre-injection ratio is set to20% and 30%,respectively,SOI1 is appropriately advanced or SOI2 is postponed,the pre-main injection interval is increased,the active material will fill thoroughly the room,the combustion is stable,the combustion duration period increases slightly.SOI1 mainly affects the premix combustion timing,which effectively reduces NOx,HC and CO by appropriate delay,and SOI2 affects the diffusion combustion timing,effectively improving the fuel combustion efficiency in advance.