Numerical Simulation Research On Combustion Mechanism Of Gasoline Engine With Syngas

Under the social background of the continuous increase of car ownership in China,the shortage of fossil energy and the emission of harmful pollutants are the two main factors that hinder the further development of the automobile industry.Based on the energy structure of "more coal and less oil" in China,from the perspective of fuel formulation,syngas from coal chemical industry is introduced into the cylinder as an alternative fuel of gasoline engine for blend combustion.In this research background,the combustion characteristics of syngas/gasoline blend fuel are studied by numerical simulation.First,the accuracy of the relevant syngas and gasoline chemical kinetic models on the prediction of combustion process parameters such as ignition delay time and laminar flame speed is verified,and the detailed syngas/gasoline chemical kinetic model is constructed as the research basis in this paper.Through the numerical simulation of zero dimensional homogeneous reaction,it is found that with the increase of the proportion of syngas in the syngas/gasoline blend,the ignition delay time of the blend fuel in the high temperature region(temperature higher than 1000 K)is gradually shortened,while the ignition delay time of the blend fuel in the low temperature region(temperature lower than 1000 K)is prolonged;The increase of initial pressure and equivalence ratio can shorten the ignition delay time,and the same effect can be achieved by increasing the H2/CO ratio in syngas.In the heat release process,the increase of syngas proportion in the blend fuel promotes the increase of heat release rate and the decrease of accumulated heat production;When the initial temperature increases,the peak of heat release rate first decreases and then increases,and the accumulated heat production decreases monotonously;The peak of heat release rate and accumulated heat production increase with the increase of initial pressure.With the increase of equivalence ratio,the peak of heat release rate and the accumulated heat production increase first and then decrease.On the other hand,with the increase of H2 content in syngas,the peak of heat release rate increases gradually.In the emission process,with the increase of the proportion of syngas in the blend fuel,the unburned hydrocarbon(UHC)emissions gradually decrease,while the CO emissions gradually increase.The increase of initial temperature promotes the increase of UHC and CO emissions,while the increase of initial pressure promotes the increase of UHC emissions but inhibits the formation of CO.At the same time,the lean combustion mode can promote the complete combustion of UHC and CO.On the other hand,the emissions of UHC and CO decrease linearly with the increase of H2 fraction in syngas.Through the numerical simulation of one-dimensional laminar flame,it is found that increasing the proportion of syngas in syngas/gasoline blend and the proportion of H2/CO in syngas can increase the laminar flame speed,and the increase of initial temperature promotes the increase of laminar flame speed,but higher initial pressure has the opposite effect.The temperature sensitivity analysis of the reaction system shows that the addition of syngas enhances the rate of chain branching reaction H+O2(?)O+OH and reaction chain H+O2(+M)(?)HO2(+M),2HO2(?)O2+H2O2,20H(+M)(?)H2O2(+M),thus accelerating the combustion reaction and increasing the flame propagation speed.On the other hand,the results of rate of production analysis show that the effect of syngas addition on n-heptane and isooctane is divided into two stages,low temperature stage and high temperature stage,according to the C-C bond fracture of C7～C8 alkanes.The addition of syngas inhibits the low-temperature oxidation rate of n-heptane and isooctane and increases the high-temperature reaction rate of n-heptane,while the reaction path of the two species does not change;The addition of syngas accelerates the reaction rate of toluene at low temperature stage,and changes the oxidation path of toluene,which makes the reaction chain shorter.Therefore,the addition of syngas changes the oxidation reaction rate and reaction path of the main components of gasoline at different temperature stages,and reflects the different effects on the ignition delay time of gasoline in diverse temperature regions.The three-dimensional numerical simulation results of syngas/gasoline dual fuel engine show that with the increase of syngas mass ratio in the blend fuel,the mean pressure and mean temperature in the cylinder,the indicated power and the peak value of heat release rate all increase first and then decrease.Meanwhile,the increase of H2 proportion in the syngas can promote the temperature and pressure rise in the cylinder.In addition,the increase of H2 component leads to the advance of the peak pressure in cylinder,which makes the heat release of engine closer to the constant volume heat release of theoretical cycle with higher thermal efficiency.With the increase of the proportion of syngas,NOx emission decreases gradually,soot emission increases monotonously,UHC emission decreases first and then increases,and CO emission increases monotonously,while CO2 emission is negatively related to the proportion of syngas.With the increase of H2 content in syngas,NOx emission is higher and soot emission is significantly reduced,while H2/CO mass ratio has little effect on UHC emission.In addition,with the increase of H2 content,CO emission decreases gradually,and CO2 emission first increases and then decreases.