Visualization study on combustion characteristics of direct-injected hydrous methanol ignited by diesel in a constant volume combustion chamber

Aiming to regulate the combustion and emission of diesel/methanol dual-fuel engine more effectively, the using of hydrous methanol was proposed in the current study. The ignition and combustion characteristics of direct -injected hydrous methanol ignited by diesel were investigated by optical diagnostics. Visualization experi-ments were conducted on a constant volume combustion chamber (CVCC) test bench with a dual-direct injection system. Diesel was injected into CVCC prior to methanol. The results show that adjusting water content in methanol and injection interval between diesel and methanol injection are two of the most important strategies that can control the ignition and combustion process. Higher water content in methanol results in much more heat absorption during water evaporation, which should be corresponding to longer ignition delay, longer flame lift-off length (FLOL) and lower spatial integrated natural luminosity (SINL). However, the decomposition of water under high temperature as well as high pressure condition can produce OH groups, which accelerates the combustion process. Moreover, the injection interval can alter the collision timing and position of spray plumes, which are very significant for diesel ignition and methanol combustion. There are almost no monotonic effect laws when water is introduced under different injection interval conditions. Suitable design and calibration of injection strategy is crucial for effective and clean combustion in diesel/hydrous methanol dual-direct injection mode.