Experimental study of the effect of hydrogenated catalytic biodiesel-Ethanol blends on combustion and soot formation process within an optical engine

The utilization of Ethanol in compression ignition engines has demonstrated great potential for reducing greenhouse gas emissions and breaking the NOX-soot trade -off relationship. However, it is usually necessary to burn ethanol with high-reactivity fuels to address its problem of high resistance to autoignition and low power output, especially during cold-start or low-load conditions. However, this combustion of high-reactivity fuels can lead to high soot emissions. This paper examines the characteristics of in-cylinder soot formation throughout two-color pyrometry in an optical engine operated in partially premixed low-temperature combustion mode, focusing on hydrogenated catalytic biodiesel/ethanol/n-octanol blends with two different proportions (75%/ 15%/10% and 60%/30%/10% by volume) and varying injection strategies. The results indicate that both blends exhibit a typical two-stage heat release process, with the highest cylinder pressure, earliest soot onset and the highest integrated KL factor occurring at an injection timing of - 25 degrees CA. By slightly compensating for power output, a higher proportion of ethanol in the blends leads to a significant in-flame soot reduction and a more uniform soot distribution within the cylinder.