汽油/柴油双燃料低温燃烧过程和排放的试验

摘要

在转速为1 900 r/min、平均指示压力为0.8 MPa的工况下,通过一台单缸高压共轨柴油机进行了不同参数对汽油/柴油双燃料低温燃烧过程影响的试验,结果表明:在给定的试验工况及边界条件下,通过调整汽油和柴油的混合比例、EGR率、柴油喷射压力及喷射正时,可以实现燃烧过程的控制和优化,发动机热效率显著提升,氮氧化物(NOx)和碳烟(soot)排放大幅降低.在汽油比例为90％、EGR率为40％的条件下,发动机热效率随柴油喷射压力的升高有所改善,HC排放呈降低趋势,soot排放则一直保持极低水平,但NOx排放升高.在此基础上进一步对柴油喷射正时进行了试验,结果表明:柴油喷射正时对该工况下的低温燃烧过程有明显影响,若柴油喷射靠近上止点,其燃烧过程受柴油传统扩散燃烧影响;若喷射正时过于提前,其燃烧过程受预混燃烧控制.通过优化第二次柴油喷射正时,发动机指示热效率达到了53.2％.%The effect of different parameters on the characteristic of gasoline-diesel dual fuel based low temperature combustion was conducted on a single cylinder diesel engine equipped with common rail fuel system at 1900 r/min and 0.8 MPa IMEP condition.The results indicate that at the selected operating condition,this low temperature combustion process can be controlled and optimized by adjusting the premixed gasoline fraction,EGR rate,diesel rail pressure and injection timing.As a result,the indicated thermal efficiency (ITE) can be improved while NOx and soot emissions can be significantly reduced.At the condition of 90％ gasoline fraction and 40％ EGR rate,the increase of diesel injection pressure makes the ITE improved,HC emission reduced and NOx emissions obviously increased.However the soot always keeps at an extremely low level.The subsequent injection timing swing test results show that the diesel injection timing has a significant impact on the low temperature combustion process.When the diesel injection timing is close to the top dead center,the overall combustion process is dominated by the diffusion combustion mode.When the diesel injection timing is advanced enough,the combustion process is then dominated and controlled by the premixed combustion mode.An ITE of 53.2％ is reached by optimizing the second injection timing of the diesel fuel.