GEM Ternary Blends of Gasoline, Ethanol and Methanol: An Initial Investigation into Fuel Spray and Combustion Characteristics in a Direct-Injected Spark-Ignition Optical Engine Using Mie Imaging

Five different fuels, including gasoline, commercial E85, pure methanol and two mixtures of gasoline, ethanol and methanol, (GEM), configured to a target stoichiometric air fuel ratio have been investigated in a fully-optically-accessed engine. The work investigated effects of injection duration, and performed spray imaging, thermodynamic analysis of the combustion and OH imaging, for two fixed engine conditions of 2.7 and 3.7 bar NMEP at 2000 rpm. The engine was operated with constant ignition timing for all fuels and both loads. One of the most important results from this study was the suitability of a single type of injector to handle all the fuels tested. There were differences observed in the spray morphology between the fuels, due to the different physical properties of the fuels. The energy utilisation measured in this study showed differences of up to 14% for the different GEM fuels whereas an earlier in-vehicle study had showed only 2 to 3%. However, there was no information about any changes imposed by the engine management system for the earlier in-vehicle study, and this work was performed without a dynamometer (load being set by operating the engine at a fixed valve timing and intake depression as per earlier work using the equipment). The combustion analysis gave some interesting results when the OH images were compared to the rate of heat release. Here, E85 showed a consistently faster burn rate to that of gasoline, whereas the combustion images appeared to show the opposite. A short section on future work details further investigations that are required to explain some of the contradictory results found in the present work.