Engine performance affected by direct injection timing in a dual ethanol injection SI engine

Publication Type:
Conference Proceeding
11th Asia-Pacific Conference on Combustion, ASPACC 2017, 2017, 2017-December
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© 2018 Combustion Institute. All Rights Reserved. Ethanol fuel, as a bioproduct, has become an alternative option to gasoline fuel in SI engines. Dual ethanol injection strategy (DualEI) is a new technology under development to maximise the benefits of ethanol’s properties to the SI engine use. The direct injection timing could significantly affect the DualEI engine performance and fuel economy. In this study, four direct injection timings were set after the intake valve closed to investigate the combustion and emissions characteristics and specific fuel consumption of the DualEI engine. Experiments were conducted at a light load (Engine torque 6.5-7.5 N.m) and four-selected spark timings at a fixed direct injection ratio. The results showed that the IMEP and engine thermal efficiency improved with advanced direct injection timing from TDC, and the indicated specific fuel consumption was reduced. As the direct injection timing works interactively with spark timing, advanced spark timing could improve the engine performance when the direct injection timing was retarded. The maximum improvement to the IMEP was 7.61%, and the indicated specific fuel consumption reduction was 7.07%. This was attributed to the improved mixture and combustion quality caused by the longer time available when the direct injection timing was advanced. The greater in-cylinder pressure and temperature could play a significant role in the engine performance improvement when the direct injection timing was retarded, and the spark timing was advanced. Consequently, the indicated specific nitric oxide (ISNO) was sharply increased because it is directly related to the burned gas temperature. On the other hand, because of the cooling effect, ISNO decreased with the retarded timing of the direct injection. The indicated specific carbon monoxide was increased with advanced direct injection and spark timings. This was attributed to the lean mixture quality caused by the decreased equivalence ratio with the advanced direct injection timing.
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