Chemical Reactivity Control of DME/Ethanol Dual Fuel Combustion

The use of renewable fuels in place of conventional hydrocarbon fuels can minimize the carbon footprint of internal combustion engines. DME has been treated as a suitable surrogate to diesel fuel because of its high reactivity and soot-less combustion characteristics. The lower energy density of DME fuel demands a higher fuel supply rate to match the engine loads compared to diesel, which was achieved through prolonged injection duration and larger nozzle holes. When used as a pilot fuel to control the combustion behavior in a dual-fuel application, the fuel energy delivery rate becomes less critical allowing the use of a standard diesel common-rail injector for DME direct injection. In this work, the combustion of DME-Ethanol dual-fuel reactivity-controlled compression ignition was experimentally investigated. Compare with diesel, the high volatility of neat DME fuel can enhance its mixing with port injected fuel even under very early fuel injection timing, which is critical for reactivity-controlled compression ignition. On the other hand, the high chemical reactivity can enhance the combustion efficiency under high ethanol ratio conditions by enhancing ignition. Both factors make DME suitable as the direct injected fuel for the dual-fuel combustion process. The impact of DME pilot injection timing and DME/ethanol ratio on combustion characteristics was investigated under various engine load conditions. The results are then compared with diesel/ethanol dual fuel combustion, to discuss the impact of chemical reactivity of direct injected fuel on dual fuel combustion process.