喷油定时与进气压力对RCCI特征参数的影响

为制定合理的活性控制压燃RCCI(Rreactivity Controlled Compression Ignition,RCCI)燃烧模式的控制策略,探明不同燃烧边界条件对RCCI燃烧与排放特性的影响,该研究在发动机转速和汽油能量预混比不变的条件下,用一台六缸重型柴油机进行了汽油/柴油双燃料RCCI试验,研究了不同循环能量(CycleEnergy,CE)下喷油定时(Startof Injection,SOI)和进气压力(Inlet Pressure,IP)对汽油/柴油RCCI燃烧和排放特性的影响规律和影响程度。结果表明,当CE从885增加到1700J时,SOI和IP对燃烧特性的影响规律不改变,但SOI和IP对缸内温度的影响程度增加,使缸内平均温度峰值分别增加约130和70 K,压力升高率峰值增加约0.054 MPa/°CA,而SOI和IP对滞燃期的影响程度不变;在排放方面,仅SOI对CO排放的影响规律发生变化,SOI和IP对HC排放的影响程度降低,使HC的排放分别减小约89和13.65g/(kW·h),IP对NOx排放的影响程度增加,使NOx的排放增加约3g/(k W·h),SOI对颗粒物总质量浓度的影响程度不变。研究结果可为制定合理的RCCI燃烧模式控制策略提供数据支撑。

Effects of start of injection and inlet pressure on characteristic parameters of RCCI

In order to make a reasonable control strategy of RCCI (reactivity controlled compression ignition) combustion mode and to explore the influence of different combustion boundary conditions on the combustion and emission characteristics of RCCI, in this paper, a six-cylinder heavy-duty diesel engine was used to test the RCCI of gasoline / diesel dual fuel under the condition of constant engine speed and gasoline energy premixing ratio. The effects and its degree of start of injection (SOI) and inlet pressure (IP) on gasoline/diesel RCCI combustion and emission characteristics were studied under different cycle energy (CE) operating conditions with a fixed gasoline energy premix ratio (PR) of 65%. The results indicated that the effects of SOI and IP on all combustion characteristic parameters hardly changed with the increase of CE. For example, the ignition delay increased with the advancement of SOI under different CE. The effects degree of SOI and IP on some combustion characteristic parameters changed with the increase of CE. For example, with the same advancement of SOI (23 °CA), the maximum of cumulative heat release was average increased by about 150 J when CE was 885 J, while the maximum of cumulative heat release was average increased by about 250 J when CE was 1 700 J, the effects degree of SOI on maximum of cumulative heat release became greater with the increase of CE. What''s more, the adjustment range of IP on the peak average temperature in the cylinder was decreased by about 130 K, when CE increased from 885 to 1 700 J, the effects degree of IP on the peak average temperature in the cylinder became greater with the increase of CE, which indicated that the adjustment capacity of IP on the in-cylinder temperature became stronger. However, the effects degree of SOI and IP on some combustion parameters did not change with the increase of CE, such as the effects degree of SOI and IP on the ignition delay, the increase of the ignition delay was almost the same (about 10 °CA) with the advancement of SOI (23 °CA) under different CE. What''s more, the change of thermal efficiency was almost the same (about 5%) with the advancement of SOI (23 °CA) under different CE. Besides, the effects of SOI and IP on the gas emissions, except the CO emission, almost unchanged with the increase of CE. In fact, when CE increased from 885 to 1 700 J, the CO emission decreased continuously. However, the increase of CE changed the effects degree of SOI and IP on some gas emissions, for example, with the same increase of IP by 15 kPa, the HC emission was average increased by about 13.65 g/(kW·h) when CE was 885 J, it remained almost the same with the CE was 1 700 J, that was, the effects degree of IP on the HC emission was greatly reduced with the increase of CE, which indicated that the adjustment capacity of IP on the HC emission became weaker. What''s more, with the same increase of IP by 15 kPa, the NOx emission was average decreased by about 1 g/(kW·h) when CE was 885 J, while the NOx emission was average decreased by about 4 g/(kW·h) when CE was 1 700 J, that was, the effects degree of IP on the NOx emission was slightly increased with the increase of CE, which indicated that the adjustment capacity of IP on the NOx emission was slightly enhanced. In addition, the increase of CE changed the effects or its degree on some parameters of particles emission. For example, the effects degree of SOI and IP on the average particle size and number concentration of nuclear particles were both decreased with the increase of CE, which indicated that the adjustment capacity of SOI and IP on the nuclear particles became weaker. On the contrary, the effects or its degree of some parameters of particles emission did not change with the increase of CE. For instance, the impact of SOI on the total mass concentration of particles was almost the same under different CE. The research results can provide data support for making a reasonable control strategy of RCCI combustion mode.