高海拔(低介质密度)下燃油喷雾与燃烧特性

Diesel Spray and Combustion Characteristics under High Altitude(Low Gas Density)

通过可视化喷雾与燃烧试验台,研究了不同海拔、低介质密度条件下燃油的喷雾和燃烧特性,并分析了各介质密度条件下不同喷射压力对燃油喷雾和燃烧特性的影响.结果表明:模拟不同海拔的发动机在高、中、低3个转速工况的缸内热力边界条件下喷雾的发展过程中,液相贯穿距先增加然后保持在相对稳定的数值,随模拟海拔高度增加,最大喷雾液相贯穿距明显增加,海拔3,000,m以上出现撞壁现象,喷雾锥角有小幅度减小,卷吸空气体积明显增大,但燃空当量比增加;海拔从0,m升高到4,500,m,着火滞燃期增加了0.2,ms,着火位置开始远离喷嘴,燃烧重心逐渐靠近壁面区域;在相同的喷孔直径下,随喷射压力升高,油束液相达到准稳态时刻提前,最大液相贯穿距基本不变,喷雾锥角略微增加,喷雾体燃空当量比减小且在高海拔变化明显,燃烧过程的滞燃期变化不大,着火位置后移.

The diesel spray and combustion characteristics under different conditions of low gas density were studied on an optical accessible diesel spray and combustion test bench. Effects of the injection pressure on the fuel spray and combustion characteristics were analyzed. The results show that, under the in-cylinder thermodynamic boundary con- ditions of three engine speeds at different altitudes, the liquid penetration distance increases first and then keeps in the relatively stable value during the spraying process. It increases significantly with the increase of the altitude. The im- pingement occurs above the altitude of 3 000 m. With the increase of altitude, the spray cone angle reduces slightly, the air entrainment area increases significantly and the fuel-air equivalent ratio increases. With the increase of altitude from 0 m to 4 500 m, the ignition delay increases by 0.2 ms, and the ignition location gradually stays away from the nozzle and close to the wall. On the other hand, with the increase of injection pressure, the time of achieving quasi- stable state is advanced, the maximal liquid penetration distance does not change significantly, and the spray cone angle is less changed. In addition, the air entrainment area increases and the fuel-air equivalent ratio reduces obvi- ously at high altitude. The ignition delay changes little but the ignition position moves backward.