Optical study on spray combustion characteristics of PODE/diesel blends in different ambient conditions

•Spray combustion of diesel/PODE blends with PODE fraction of 0–100% was studied.•Ignition delay decreases more in higher ambient temperature and higher EGR condition.•Flame lift-off length shows increasing tendency when more PODE is added.•When the PODE fraction is more than 50%, nearly no soot was observed.•Soot reduction caused by PODE addition weakens in high temperature and EGR cases. Polyoxymethylene dimethyl ethers (PODE) have been reported as a promising alternative fuel for the potential to reduce soot, CO and HC emissions of the diesel engine and improve the engine performance of gasoline compression ignition and dual-fuel engines. However, the fundamental data of spray and combustion characteristics of fuels with PODE are still deficient. In this study, the ignition delay, flame lift-off length (LOL) and soot distribution of diesel/PODE blends with PODE volume fraction of 0–100% were studied using high-speed OH chemiluminescence and planar laser-induced incandescence under different ambient temperature and oxygen concentration conditions. Results show that the ignition delay decreases and the flame LOL increases with the increase in PODE content. The increase in LOL is more distinct in lower ambient temperature conditions, whereas the decrease in ignition delay is relatively larger in higher temperature and lower oxygen concentration conditions. The total soot amount in the tested region decreases more than 50% and 95% when PODE volume fraction reaches 20% and 50%, respectively. When the PODE fraction is larger than 50%, nearly no soot can be observed in all the tested cases. The influence of PODE on soot reduction is more significant in higher ambient oxygen concentration and lower ambient temperature conditions. The soot distribution profile of the soot shows that the addition of PODE can not only reduce the soot formation but also accelerate the soot oxidation.