无节气门汽油机燃烧循环变动特性试验

Experiment of Combustion Cyclic Variations in Unthrottled SI Engine

一种全可变液压气门机构(FHVVS)可实现气门升程和开启持续期的连续可变,采用进气门早关的方式可取代节气门实现无节气门负荷控制方式.通过试验测量缸内压力,发现无节气门汽油机在小负荷工况下的燃烧循环变动明显增大,燃烧速率显著降低.通过增大点火提前角,使燃烧重心(CA 50)调整至5°~10°,CA ATDC的推荐位置,却导致出现失火循环.探讨了通过组织进气涡流和增大点火能量的方式改善燃烧性能,结果表明:螺旋进气门能够在小升程时产生较强的进气涡流,显著改善了无节气门汽油机在小负荷工况下的燃烧循环变动和失火循环,提高了指示热效率;增大点火能量对改善燃烧循环变动也有一定作用.

A fully hydraulic variable valve system （FHVVS）was developed to vary the valve lift and opening duration con- tinuously in a spark ignition （SI） engine. The unthrottled load control mode was then achieved by using early intake valve closing （EIVC） mode instead of throttle. The cylinder pressures measured in the unthrottled SI engine show that the combus- tion cyclic variations are obviously increased and the burning rates are significantly reduced under low load operations. The center of heat release （CA 50） can be adjusted to the recommended position of 5^--10~ CA ATDC by increasing ignition ad- vancing angle, but some misfire cycles occur unfortunately at this condition. An attempt to improve the combustion process was conducted by increasing the intake swirl and the ignition energy. The results show that a helical intake valve with spiral grooves on the back of the valve enhances the intake swirl under the small valve lift, leading to remarkably improvement of the cyclic variations, misfire cycle and the indicated heat efficiency under low load conditions. The enhanced ignition energy also has a certain effect on the improvement of cyclic variations.