Combustion Characteristics and Exhaust Emissions of a Direct Injection SI Engine with Pure Ethanol and Methanol in Comparison to Gasoline

The automobile industry is under intense pressure to reduce carbon dioxide (CO₂) emissions of vehicles. There is also increasing pressure to reduce the other tail-pipe emissions from vehicles to combat air pollution. Electric powertrains offer great potential for eliminating tailpipe CO₂ and all other tailpipe emissions. However, current battery technology and recharging infrastructure still present limitations for some applications, where a continuous high-power demand is required. Furthermore, not all markets have the infrastructure to support a sizeable electric fleet and until the grid energy generation mix is of a sufficiently low carbon intensity, then significant vehicle life-cycle CO₂ savings could not be realized by the Battery Electric Vehicles.

This investigation examines the effects of combustion, efficiencies, and emissions of two alcohol fuels that could help to significantly reduce CO₂ in both tailpipe and the whole life cycle. The alcohol fuels have been compared to a RON95 E10 gasoline that conforms to EN228 and represents the main gasoline fuel in the EU. The experimental work was carried out at Brunel University London, where the fuels have been tested using a single cylinder version of the MAHLE Powertrain downsized engine, which can operate at brake mean effective pressure levels of up to 30bar.

The paper presents results showing detailed combustion analyses, across a focused operating region, taking into consideration both high-load conditions at multiple speeds, as well as lower engine load and lower temperature spark retard conditions. In addition, the direct injection settings for each fuel will be characterised, to understand the effects of injection parameters on the engine efficiency and emissions performance for each fuel. Furthermore, particle number and size distribution has been measured and analysed for the three fuels. The results show the potential benefits of alcohol fuels, and design considerations that could be made to optimize for the use of pure ethanol and pure methanol in a direct injection spark-ignited internal combustion engine.