Optical characterization of methanol compression-ignition combustion in a heavy-duty engine

Methanol is a low sooting fuel that can potentially be used in compression-ignition engines despite its high resistance to auto-ignition and reduce emissions while maintaining high engine efficiency. Due to the auto-ignition resistance, few studies of methanol compression-ignition exist and even fewer are conducted in an optically accessible engine. In this paper, two cases of premixed combustion and two cases of spray-driven combustion of methanol were investigated in a heavy-duty optically accessible engine. Ignition and combustion propagation were characterized with a combination of time-resolved natural flame luminosity measurements and single-shot, acetone fuel-tracer, laser induced fluorescence. Mie-scattering was used to identify the interaction between liquid spray and ignition sites in spray-driven methanol combustion. Results demonstrated that methanol combusts drastically different compared to conventional fuels, especially in spray-driven combustion. The evaporative cooling effect of methanol appears to play a major role in the auto-ignition characteristics of the delivered fuel. Ignition sites appear right at the end of injection when the evaporative cooling effect is withdrawn or at liquid length oscillations where, again the effect is momentarily retracted.