Simulation Research On Dual Fuel Compression Ignition Combustion Of Diesel Engine

With the increasing degree of dependence on foreign oil and the stringent emission regulations,the research on new energy vehicles using unconventional fuels as energy sources has become a hot topic for the national government,automobile manufacturers and major research institutions.Methanol has many advantages,such as wide source,low price and clean oxidation and so on.It has a enormous advantage as a kind of alternative fuel for gasoline and diesel oil.But there are still urgent problems to solve such as compression ignition difficulty and low operating conditions due to its high octane number and high latent heat of vaporization.In this paper,diesel igniting methanol air premixed gas combustion mode were used in diesel engine.Inject methanol early to form methanol air mixture.Diesel as the ignition fuel is injected before TDC.Firstly,the FIRE software was used to analyze the cold flow of a complete cycle to study the variation trend of turbulent flow energy and velocity field in the cylinder.Then,investigate the effect of fuel methanol quality ratio on combustion and emission characteristics and compare with the original diesel engine.Finally,changing the engine parameters such as methanol mass ratio,diesel ignition timing,compression ratio and initial temperature to investigate trend of engine combustion characteristics and emission characteristics.The results showed that,compared with the original diesel engine,at 40% methanol mass ratio,the power index is better,the CO and SOOT emission is greatly decreased and the NO emission is slightly higher.With the increase of methanol mass ratio,the peak value of pressure and heat release rate decrease and harmful substances emission increase slightly.With the change of methanol injection time,the combustion and emission characteristics of the engine are nonlinearity,and the combustion and emission characteristics are best at 70°CA BTDC.The effect of compression ratio for the premixed combustion mode is the same as conventional diesel engine.With the increase of the compression ratio,the peak of the combustion characteristics is increased,and the emission of other harmful substances is improved except for the slight increase of NO emission.With the change of diesel injection time,the combustion and emission characteristics have obvious fluctuation.Appropriate advance injection timing can advance the ignition of methanol air mixture,the combustion timing and peak heat release rate close to the crank angle of TDC,get better combustion and emission characteristics.The results also show that the combustion of methanol premixed gas is sensitive to the initial temperature of in cylinder.The low temperature led to the obvious delay of combustion timing and significantly increased of the harmful emissions.The engine bench test of different methanol mass ratio for the combustion characteristics are same as simulation test,but there are some differences on emission characteristics.the emission of CO and SOOT is greatly decreased.The combustion and emission characteristics can be improved by appropriately increasing the compression ratio and changing the injection advance angle.Above all,Methanol and premixed gas combustion mode combined have bright development.By changing the injection strategy and engine parameters can effectively improve the combustion and emission characteristics.