Simulation Research On Combustion And Emission Characteristics Of Dual Methanol/Diesel Direct Injection HCCI Engine

The use of methanol as a fuel can greatly reduce the degree of dependence on external oil.And it contains oxygen,which is a clean fuel.In the paper,a certain three-cylinder diesel engine is used as the original engine,and transform it into a dual direct injection methanol/diesel HCCI engine by installing an methanol injector.And using Converge 3D fluid simulation software to build a simulation model and simulate it.The effects of methanol energy ratio,methanol injec-tion timing and pressure,and different nozzle diameter settings on the combustion and emis-sions of dual direct injection methanol/diesel HCCI engine in cylinders under full load condi-tions of 1200r/min and 2400/min are investigated.The conclusions as follow:Compared with the original engine,the increase in methanol’s energy ratio will gradually extend the flame retardation period.This is conducive to the further mixing of methanol pre-mix.At the same time,The combustion of methanol is faster.The combustion pressure,temper-ature and the pressure rise rate in the cylinder increase.Since methanol contains oxygen,add it into combustion can greatly reduce the generation of SOOT,HC and CO emissions.But it also makes the NO_x emission at low speed higher than the original engine.With the delay of methanol injection,the mixing degree of methanol and air decreases.It hinders the spread of flame when burning and prolong the burning period.At the same time,the cylinder pressure,cylinder temperature and pressure rise rate decrease.At low speed,SOOT emissions decrease with the delay of methanol injection.NO_x and CO emissions rise.At high speed,the emissions show an irregular trend.With the increase of methanol injection pressure,SMD has shown a downward trend.The mixture in the cylinder also gradually tends to be homogeneous.Ignition delay increases but the combustion duration decreases.The combustion pressure and temperature in the cylinder have also increased to varying degrees.The rate of pressure rise increases,and the combustion is relatively rougher.The increase in methanol injection pressure increases emissions at low speed.Except for HC,the other emissions are higher than the low injection pressure.The per-formance at high injection pressure under high speed is better.Under the working condition of 1200r/min full load,the nozzle area of the intake direction is increased by 20%,and the nozzle area of the exhaust direction is reduced by 20%,which is beneficial to the uniform distribution of methanol with the intake airflow.It shortens the flame retardation period and combustion duration,increase the pressure in the cylinder during combustion and reduce the pressure rise rate.Increasing the nozzle diameter on the intake side slightly increases SOOT emissions and reduces NO_x,HC and CO emissions.