PLII-LEM and OH* Chemiluminescence Study on Soot Formation in Spray Combustion of PODEn-Diesel Blend Fuels in a Constant Volume Vessel

Polyoxymethylene dimethyl ethers (PODEn) are promising alternative fuel candidates for diesel engines because they present advantages in soot reduction. This study uses a PODEn mixture (contains PODE_3-6) from mass production to provide oxygen component in blend fuels. The spray combustion of PODEn-diesel bend fuels in a constant volume vessel was studied using high speed imaging, PLII-LEM and OH* chemiluminescence. Fuels of several blend ratios are compared with pure diesel. Flame luminance data show a near linear decrease tendency with the blend ratio increasing. The OH* images reveal that the ignition positions of all the cases have small differences, which indicates that using a low PODEn blend ratio of no more than 30% does not need significant adjustment in engine combustion control strategies. It is found that 30% PODEn blended with diesel (P30) can effectively reduce the total soot by approximately 68% in comparison with pure diesel. The profile of the soot distribution of the P20 and P30 cases are different to that of diesel because the high oxygen contents in PODEn result in significant differences in soot formation and the oxidization process. The statistics results of the soot distribution indicate that the soot reduction effect of PODEn occurs not only because the high oxygen contents of PODEn promote oxidization, but also related to the absence of a C-C bond in the molecule which suppresses the generation tendency of soot precursors.