The efficient ethanol engine with cold start capability
Sammanfattning: In light of the world’s growing demand for personal transportation and the decreasing availability of fossil fuels, alternative fuels must be evaluated. Ethanol is a renewable fuel whose adoption could help to reduce the burden of anthropogenic activity on the environment. In addition to being renewable, it has properties that make it an ideal fuel for spark-ignited engines, such as its high octane number and oxygen content. Today, ethanol is widely available as a blended fuel containing 15% gasoline that is known as E85. Furthermore, all gasoline sold today in Europe and the USA has an ethanol content of approximately 10%. The project described in this paper was conducted to investigate the scope for modifying a contemporary SI engine to make optimal use of neat ethanol as a fuel. A state-of-the-art gasoline engine was acquired and modified by fitting it with stronger mechanical parts and a two-stage turbo system, and increasing its compression ratio (to 13:1). The modified engine uses piezo-actuated, outwards-opening, injectors to inject fuel into the cylinders via a fuel system that can generate injection pressures of up to 200 bar. The mass flow through the injectors can be controlled by varying the opening of the pintle, making it possible to achieve a wide range of injection rates and durations while exercising precise control over the mass of fuel injected. This is very useful in enabling the engine to run on both gasoline and ethanol because the two fuels have different heating values. Moreover, the injectors are capable of delivering a fuel cloud with good separation from the surrounding air, which is essential when using stratified combustion. One major problem faced by contemporary flex-fuel vehicles is their limited ability to achieve cold starts. In winter, it is necessary to increase the amount of gasoline blended into E85 to facilitate starting in cold weather. However, the results presented herein demonstrate that when using stratified combustion with neat ethanol as the fuel, it is possible to achieve cold starts at very low temperatures (in a single cylinder engine) without outside assistance. The modified 4-cylinder engine was shown to have an excellent fuel consumption of 310 g/kWh at 2000 rpm and 2 bar due to its use of stratified combustion, while still providing ~30 bar BMEP at wide open throttle. When the engine was tested on gasoline, the number of soot particles produced was six times greater than when using ethanol at the 2000 rpm, 2 bar test point. This implies that particle traps, which will probably be required on direct injection gasoline vehicles to satisfy the requirements of future laws on emissions, may be unnecessary for engines that burn ethanol exclusively. In conclusion, this project has demonstrated that it is possible to achieve cold starts at -23°C when using neat ethanol as fuel, and that this approach produces very low emissions of un-burned hydrocarbons. The maximum efficiency of the modified engine is estimated to be over 37%, which is greater than most SI engines currently on the market. Moreover, the modified engine offers a downsizing potential of 43% relative to a state of the art naturally aspirated engine, producing slightly more power (more than 300 bhp overall) with 19% lower fuel consumption at a vehicle speed of 70km/h. If the concept were downsized further, to “only” supply ~200bhp, the fuel consumption at this vehicle speed could be decreased by a further 15%. Ultimate performance have been predicted in modelling efforts and verified in test bench. The factors that made these results possible are ethanol’s high knock resistance in conjunction with the use of stratified combustion and a two-stage-turbo charging system.
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