The Numerical Simulation Analysis Of Combustion Of Methanol-diesel Blends

Energy conservation and emission reduction are permanent tasks for the study of the internal combustion engine. Finding suitable alternative fuels is one of the most effective means to solve these two problems. Methanol, as a very good alternative fuel, has become an advanced research hotspot. Methanol can be derived from a wealth of sources, meanwhile, it can promote complete combustion of diesel fuel and reduce emissions. The quality of the internal combustion engine performance is mainly controlled by the process of combustion in the cylinder. The research applied emulsification to mix diesel and methanol, conducted numerical simulations on combustion of methanol-diesel blends to explore the performance of the alternative energy.Based on combustion simulation software AVL FIRE in this research, we select WD615 series diesel engine as the research object to simulate the combustion process. We set methanol-diesel blends, and the methanol volume fraction were prepared 5%(M5), 10%(M10), 15%(M15). Under the premise of a certain cyclic injection mass and the low calorific value of fuel, our simulation results were compared with the results of the original machine:On the one hand, the cyclic injection mass unchanged, with the increase in the proportion of methanol, the average maximum cylinder pressure decreasing on account of the net heating value of methanol is slightly lower than half of diesel. However, the peaks of the average maximum cylinder pressure are both in the vicinity of the crank angle of 367°CA, and the temperature in the cylinder is also slightly lowered. After adding methanol fuel in diesel, dynamic property of the internal combustion engine has declined. Using methanol fuel, the speed of combustion raises, combustion duration shortens, heat released by burning is less than using conventional fuels, and the heat release rate reduces, thermal efficiency raises, economical efficiency of the internal combustion engine is improved. Heat of vaporization of methanol is large, temperature of the mixed gas in the cylinder reduces, thus, with the increase in the proportion of methanol added, emissions of nitrogen oxide reducing. After adding methanol fuel, the ignition delay period is extended and speed of methanol combustion raises, under the combined effect of these two factors, when the proportion of methanol is prepared more than 5%, soot emissions will reduce. Compared with diesel, using M10 and M15, soot emissions decreases by 6.9% and 17.7%, while using M5, the number almost flats.On the other hand, the low calorific value fuel is constant, with the increase of the proportion of methanol, cyclic injection mass added, injection moved up, maximum cylinder pressure increased, the temperature lowered, emissions of nitrogen oxide and soot have decreased. Different intake pressure, temperature and fuel injection timing of its impact is as follows:(1) Intake pressure and temperature affect the amount of intake air in the diesel engine and ignition delay of the combustion process. To maintain constant intake air temperature, as the intake pressure increases, cylinder pressure and pressure rise rate increases, nitrogen oxides and soot emissions reduce. To maintain constant intake pressure, as the intake air temperature increases, cylinder pressure drops, temperature increases, emissions of nitrogen oxides and soot increases.(2) Injection timing affects the combustion process of the diesel engine and it’s performance. As injection advances, start of combustion advances, cylinder pressure and pressure rise rate increases, the temperature rises, the nitrogen oxide emissions of the cylinder increase, however, law of soot emissions remains unknown on account of injection timing. Thus, during the actual working process of the engine, we should select proper injection timing according to specific situation.