Optical Characterization of Methanol Sprays and Mixture Formation in a Compression-Ignition Heavy-Duty Engine

Methanol is not a fuel typically used in compression ignition engines due to the high resistance to auto-ignition. However, conventional diesel combustion and PPC offer high engine efficiency along with low HC and CO emissions, albeit with the trade-off of increased NOx and PM emissions. This trade-off balance is mitigated in the case of methanol and other alcohol fuels, as they bring oxygen in the combustion chamber. Thus methanol compression ignition holds the potential for a clean and effective alternative fuel proposition. Most existing research on methanol is on SI engines and very little exists in the literature regarding methanol auto-ignition engine concepts. In this study, the spray characteristics of methanol inside the optically accessible cylinder of a DI-HD engine are investigated. The liquid penetration length at various injection timings is documented, ranging from typical PPC range down to conventional diesel combustion. Three matched engine operating conditions are studied, where the effective variant is injection pressure alone. The liquid penetration length and cone angle are characterized by Mie-scattering and the effect on fuel distribution is visualized via fuel-tracer PLIF. Finally, the liquid penetration length of methanol is compared to commonly used PRF81 gasoline, demonstrating a stark dependence on ambient conditions.