Effect of Ethanol Reforming Gas Combined with EGR on Lean Combustion Characteristics of Direct Injection Gasoline Engine

Ethanol reforming gas combined with EGR technology can not only improve thermal efficiency, but also reduce pollutant emission under lean combustion condition. In this investigation, GT-Power is used to carry out one-dimensional simulation model calculation and analysis to explore the combustion characteristics, economy performance of a direct injection gasoline engine when the excess air coefficient (λ) increases from 1 to 1.3 and the ethanol reforming gas mixing ratio increases from 0% to 30% at the working condition of 2000 r/min and 10 bar. Then the EGR system is introduced to deeply discuss the working characteristics of the direct injection gasoline engine when the EGR rate increases from 0% to 20%. The results show that the increase of λ leads to the decrease of in-cylinder pressure and the delay of the peak of cylinder pressure. After introducing 20% reforming gas, the combustion environment is improved, the maximum cylinder pressure and pressure rise rate can increase by 35%, the flame development period and rapid combustion period are shortened noteworthy, the cyclic variation coefficient of the maximum cylinder pressure under dilution condition is reduced by 3.5%, and the thermal efficiency is further improved. It is worth noting that fuel RE20 has the highest heat release rate and thermal efficiency, meanwhile, it also generates lowest ignition delay and the cyclic variation coefficient of the maximum combustion pressure compared with other fuels within λ from 1.0 to 1.3. Besides, the introduction of EGR reduces the combustion pressure and temperature. The cylinder pressure peak decreases by 42.5% and the rapid combustion period increases by 19° CA with 20% EGR. Eventually, the synergistic effect of reforming gas can effectively alleviate the combustion deterioration.