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

In order to make a reasonable control strategy of Reactivity Controlled Compression Ignition (RCCI) 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 (PR). 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 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 from 110 to 125 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.