Simulation Research On Effects Of Injection Strategy On Combustion And Emission Of Direct Injection Methanol Engine

With the increasing demand of fossil fuels, the energy crisis and environmentalpollution have become two major issues in this century. In order to find an efficient andclean fuel, a large number of scientific studies have been conducted. Methanol (CH3OH) istreated as an alternative fuel with great potential because of its unique properties: higheroctane number, better antidetonating quality, higher latent heat of vaporization, strongerability of lean burning and convenience in fuel transportation, storage and utilizationconsidering methanol’s physical and chemical characteristic similar to gasoline and diesel,which enlightens the combination of methanol and direct injection engine. By using theAVL-FIRE simulation software, the dynamic meshing based on the original3d model isfinished, as well as setting the boundary parameters through the bench test and verifying thefeasibility of the model. The following conclusions are drawn with the study that how theinjection strategy influences combustion and emissions in direct injection methanol engine:1. Under equivalent air-fuel ratio, ignition timing has a great effect on the formation ofthe mixture in cylinder, the combustion process and emissions. With the delay of ignitiontime, the average in-cylinder pressure decreases, the peak value of the average temperaturein cylinder decreases, the NO generation comes down and the soot generation increases.2. Under equivalent air-fuel ratio, double injections have a great effect on theformation of the mixture in cylinder, the combustion process and emissions. With theincrease of fuel injection proportion, the average pressure in cylinder increases, the peakvalue of the average temperature in cylinder increases, the NO generation becomes largerand the Soot generation decreases.3. Under equivalent air-fuel ratio, the second fuel injection time has little effect on theformation of the mixture in cylinder, the combustion process and emissions. With the secondfuel injection time delays, there is little influence of the average in-cylinder pressure and the average in-cylinder temperature, the NO generation comes down and the Soot generationincreases.4. Through the comparison between the double injection strategy and the singleinjection during the intake stroke under equivalent air-fuel ratio, we find that the NOgeneration decreases by nearly40%and the cylinder pressure decreases by4%comparing tothe single injection situation. The soot generation is more than that of the single injection.5. In the lean burning mode, ignition time has a great effect on the average in-cylinderpressure and heat release rate. With the ignition time delays, the average in-cylinder pressuredecreases, the peak value of the average in-cylinder temperature decreases, the NOgeneration comes down and the soot generation increases. The overall mixture lowconcentration during lean burning slows down the flame propagation speed in combustionprocess. In order to make the engine work stably, we should advance the ignition timeproperly, making the better ignition time17°CA BTDC earlier than that when λ=1, theignition time is23°CA BTDC.6. With the fuel injection proportion increases in lean burning mode, the averagein-cylinder pressure increases, the peak value of the average temperature in cylinderincreases, the NO generation becomes larger and the soot generation decreases. Thein-cylinder air flow grows stronger than that of equivalent air-fuel ratio mode. The amountsof the fuel later injected into the cylinder become less and the influence on the air flow madeby the oil bunch from the fuel spray nozzle decreases.7. Through the comparison of the double injection strategy and the single injectionduring the compression stroke under lean burning mode, the in-cylinder pressure increasesby3.6%, the NO generation increases by nearly30%and the soot generation decreases morethan50times.