Study of the soot quantification for two-stage injection of hydrogenated catalytic biodiesel in a constant-volume combustion chamber

Abstract

The effect of two-stage injection strategies on the soot formation of 0# fossil diesel were investigated experimentally using a constant volume combustion chamber. The ambient conditions was kept constant as injection pressure 150 MPa, ambient gas temperature 900 K, ambient gas pressure 45 bar. A high-speed diffused back-illumination extinction imaging technique was employed to make quantitative measurement on temporal soot evolution and reacting spray liquid length and a direct high-speed camera was used to measure the ignition delay. Two-stage injection strategies were varied with different pilot and main injection time, including a sweep of dwell time in pilotmain injection and pilot injection duration. The results show that the ignition delay decreases with the increasing dwell time. It may result from the entrained surrounding gas enhance the spray combustion process. In the reacting condition, the liquid-phase penetration is slightly longer with the shorter dwell time. However, the pilot injection duration shows slighter impact. The longer dwell time contributes to more total soot mass while the different pilot injection duration barely affect the total soot mass of the main injection. In non-reacting conditions, the spray of the main injection penetrates faster within a shorter dwell time investigated by Mie-scatter and CFD models [8]. When the two-stage injection duration are same, the second injection vapor phase penetration is longer and faster [9][10][11] [12]. For combustion characteristics, ignition delay of main injection is much shorter than that of the pilot injection and it may be shorter or longer with the dwell time increasing due to the different entrainment of surrounding gas [8]. In the multiple injection strategy investigation, the dwell time between injections and the pilot injection duration were seen as the two main factors. Seong-Young Lee et al. [13] found that it exists a slight reduction of the soot mass at the 0.3/0.65/1.2 ms condition. Fang et al. [14]measured the soot production of the biomass to liquid fuel using multiband flame measurement and two-color pyrometry. They found that the pilot injection results in a lower soot level compared with single injection with the same injection quality, while the pilot injection shown little impact on No. 2 diesel soot generation. However, in the study of [15], more fuel quantity during the first injection resulted in less soot emission with no increase in NOx emission when the pilot injection quantity is relative small to the main injection. Coupling the two factors, Carlucci et al. [16] found that both injection timing and duration show similar effect on the soot formation and oxidation. From the discussion before, in conslusion the soot formation in the multiple injection strategy isn't still precisely understanding. In this study, the ignition delay, reacting spray liquid length and total soot mass evolution of 0# fossil diesel were measured in a high-temperature high-pressure constant volume combustion chamber, the objective i...

Experimental study of the influence of the fuel and boundary conditions over the soot formation in multi-hole diesel injectors using high-speed color diffused back-illumination technique

“…Mass of soot was calculated with an assumed density of 1.8 g/cm 3 for soot, this value was determined by Choi et al [35], studying the collected soot from an acetylene/air premix fame and using a helium pycnometry to determine the value of the density. Same density value has been used in similar studies with diesel injectors and similar optical vessels [36,15].…”