Experimental study of alcohol fuels on engine performance, efficiency and emissions

Abstract

In order to reduce emissions of carbon dioxide (CO2) to minimize global warming and climate change, and pollutants emissions from vehicles for better air quality, it is necessary to improve the efficiency and minimize pollutant emissions from internal combustion engines by means of better engine technologies and low/zero carbon fuels, as well as the electrification of the powertrain system in vehicles. Renewable ethanol and methanol are the two alcohol fuels which can significantly reduce CO2 emissions. In this project, a state-of-art single cylinder spark ignition (SI) engine and testing facility were set up and used to study the combustion characteristics, fuel efficiency as well as gaseous and particle emissions from the engine operations with ethanol or methanol. The engine performance and the combustion process of ethanol and methanol were measured and compared with E10 RON95 gasoline. The first part of the study was carried out at three engine speeds of 2000rpm, 3000rpm and 4000rpm under different load conditions with the same engine parameter settings (cam timings, injection parameters) for gasoline, ethanol and methanol to have a direct comparison between alcohol fuels and gasoline. Particular emphasis was on the high load operations at and above 16bar IMEP when gasoline engine operation was found to be prone to knocking combustion and over-fuelling was introduced to keep the exhaust gas temperature below 780°C. In comparison, engine could be operated at stoichiometric conditions without exceeding the exhaust gas temperature limit due to their higher enthalpy of evaporation and the use of MBT timings without knocking combustion for ethanol and methanol. The result shows that methanol leads to 3.6% higher brake thermal efficiency than gasoline, and ethanol by 3.3% when operated at higher load operations at around 18bar IMEP. Both ethanol and methanol fuels lead to substantial reductions in the emission of particles, with the particle numbers reduced by up to 90%. The second series of experiments were then carried out to find the best injection strategies for ethanol and methanol. The result shows that both ethanol and methanol have larger best efficiency island than gasoline because of their greater evaporation and charge cooling effect. In addition, there’s also a reduction in emission across the fuel matrix testing. Finally, a low speed & load spark timing sweep was carried out to assess the performance of the engine fuelled by ethanol and methanol under catalyst light off condition. The result shows that both ethanol and methanol could operate with more retarded spark timings than gasoline to enable by faster catalyst-light-off. In addition, particulate emissions released by alcohol fuels are much less and of smaller sizes. The novelty of the work is enabling detailed systematic analysis of alcohol fuelled combustion, fuel consumption, performance and emissions under advanced, highly boosted SI engine conditions. The load sweep part fills in the gap of high load test conditions of pure ethanol/methanol fuelled SI engine. The fuel matrix part presents the effect of injection timing and injection pressure variation on fuel efficiency, combustion characteristic and emissions which gives a deeper understanding of air-fuel mixture of ethanol and methanol benefit from their greater evaporation and charge cooling effect. The cold start spark timing sweep shows that both ethanol and methanol could operate with more retarded spark timings than gasoline to enable by faster catalyst-light-off.