Numerical Simulation Of Plasma Enhanced Combustion Of Methane

Nowadays,the traditional internal combustion engine is developing towards the direction of higher pressure,low flame temperature and thin combustion.As the fourth kind of physical state of aggregation,Plasma can collide with fuel molecules to produce the effect of high temperature and catalytic which will effectively accelerate fuel oxidation,shorten ignition delay time and improve the speed of flame propagation so as to strengthen the ignition and combustion.In this paper,the influences of plasma on the ignition and combustion characteristics of methane/air are studied through numerical simulation platform.The main research contents and conclusions are as follows:Firstly,the independent programming of sub modules is carried out by using the open source CFD software OpenFOAM according to the requirements.Besides,the theoretical basis,composition and application of the software are introduced in this paper.A hedging laminar premixed model is also established to analyze the combustion process.The results show that the plasma distribution is closely related to the combustion process of methane,which promotes the ignition and combustion.Secondly,based on the detailed chemical kinetic mechanism GRI-MECH 3.0,the chemistry kinetics analysis software is applied to analyze the methane combustion.The influence of different factors such as the kinds and concentrations of plasma on the ignition delay,combustion characteristics and changes of heat release rate of methane combustion are explored in this paper.The results show that the addition of plasma can not only shorten ignition delay time,but also increase the maximum pressure and temperature in cylinder.Moreover,the effect of O radical is better than that of H radical.By comparing the effects of free radical O with the concentration of 0.5%,1% and 1.5%,respectively,on the combustion characteristics of methane,it is demonstrated that in-cylinder pressure and temperature is improved with the increase of the concentration of O radical,which promotes the process of combustion.However,when the concentration of O is too high,the effect of free radical on ignition and combustion-supporting is not obvious.With the addition of free radicals,the ignition time is advanced and the heat release interval between each partition decreases,which makes the heat release process more concentrated.Finally,on the basis of the above combustion mechanism,by coupling and simplifying the reaction mechanism of natural gas and ozone(O3)properly,this paper explores the influence of the trace additive O3 on the combustion characteristics of the natural gas HCCI engine.The influences of inlet pressure,compression ratio and other initial parameters on combustion and emission characteristics are also studied.The results indicate that the addition of ozone can obviously improve the combustion characteristics of the engine,shorten ignition delay time and increase the peak values of temperature and pressure.Under the condition that the concentration of O3 is 40 ppm,the ignition time can be advanced by increasing the intake temperature,the inlet pressure and the compression ratio,but the ignition time will be delayed by the increase of the equivalent ratio.Furthermore,the increase of ozone concentration and the inlet air temperature will improve the production of NOx dramatically.