Investigation to direct ethanol injection in spark ignition gasoline engines
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Ethanol is a promising alternative fuel in terms of addressing future energy and environmental problems. The existing method of using ethanol fuel by blending gasoline and ethanol fuel does not fully exploit ethanol’s advantages. The dual-fuel injection strategy, ethanol direct injection plus gasoline port injection (EDI+GPI), offers a potentially new way to make use of ethanol fuel more effectively and efficiently. The effect of EDI+GPI on engine performance has been experimentally investigated on a 249cc, 4 stroke, air cooled single cylinder engine which was modified by adding an ethanol fuel direct injection system. The research purpose was focused on efficiency improvement (leveraging effect) and emissions reduction. Engine performance at original engine spark timing setting (15 CAD BTDC), knock margin and lean conditions was carried out to assess EDI+GPI’s effectiveness. The impacts of EDI+GPI on engine control parameters, such as start of injection (SOI) timing and spark timing, were also evaluated in order to best match this new fuelling system to conventional SI engines. When the engine was operating at the original engine spark timing setting (15 CAD BTDC), less energy input was required in a SI engine equipped with EDI+GPI to achieve comparable engine power output. Thus, the total fuel consumption could be reduced by leveraging the use of ethanol fuel. At engine speed of 3500rpm, when the ethanol energy ratio (EER) was less than 42.4% at light load and 36.3% at medium load, the EDI+GPI showed a positive impact in relation to combustion with reduced combustion duration and advanced central combustion phasing. However, with further increase of EER, the combustion duration prolonged and central combustion phasing retarded. This may be caused by over cooling due to increased ethanol fuel directly injected. EDI+GPI effectively mitigated engine knock and permitted more advanced spark timing and higher inlet air pressure. At three tested engine loads of indicated mean effective pressure (IMEP), 7.2 Bar, 7.8 Bar and 8.5 Bar, every 2% or 3% increment of EER permitted about 2 CAD advance of knock limited spark advance (KLSA) when the EER was in the range from 15% to 35%. The highest load achieved in this investigation was 10.5 Bar IMEP at inlet (compressed) air pressure of 1.4 Bar. The EER level at this condition was 36.9%. Early ethanol direct injection (EEDI) was more suitable to the EDI+GPI engine since the IMEP in EEDI conditions was greater than that in later ethanol direct injection (LEDI) conditions due to improved volumetric efficiency and combustion. LEDI was less effective on increasing IMEP because its major combustion duration was longer than that in the EEDI condition. In lean burn, EEDI was more effective on extending the lean burn limit than LEDI. The maximum lean burn limit (λ) achieved by EEDI was 1.29. LEDI only slightly increased the lean burn limit which was just over the stoichiometric air-fuel ratio (AFR). When the EER varied, spark timing required corresponding changes to achieve the best efficiency. At IMEP of around 4.0 Bar, spark timing of 25 CAD BTDC resulted in the highest indicated thermal efficiency when the EER was less than 29%, whilst when the EER was greater than 39%, the maximum indicated thermal efficiency was at spark timing of 30 CAD BTDC.
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