The Effect of Direct Injection Timing and Pressure on Engine Performance in an Ethanol Direct Injection Plus Gasoline Port Injection (EDI+GPI) SI Engine 2013-01-0892

Ethanol direct injection plus gasoline port injection (EDI+GPI) is a new technical approach to make the use of ethanol fuel more effective and efficient in spark ignition (SI) engines. Ethanol fuel direct injection timing, as one of the primary control parameters in EDI+GPI engines, directly affects the quality of the fuel/air mixture and consequently combustion and emissions. This paper reports the experimental investigation to the effect of ethanol injection timing and pressure on engine performance, combustion, emissions of a single cylinder SI engine equipped with EDI+GPI. Firstly, the effect of EDI timing before and after the inlet valve closing, defined as early and late injection timings (EEDI and LEDI) was investigated at three injection pressure levels of 40 Bar, 60 Bar and 90 Bar and a fixed ethanol/gasoline ratio. Spark timing was fixed at original engine setting to investigate the potential engine efficiency improvement due to the EDI solely. Experimental results showed that the engine IMEP in EEDI conditions was greater than that in LEDI conditions due to improved volumetric efficiency and combustion. EDI pressure had insignificant effect on IMEP in EEDI conditions. In LEDI conditions high injection pressure led to increased IMEP at EDI timing of 50 CAD BTDC but decreased IMEP at 110 CAD BTDC. EEDI resulted in lower CO and higher NO emissions than in LEDI conditions. The effect of EDI timing on HC emissions was not significant. HC and CO emissions in EEDI conditions and EDI pressure of 90 Bar were lower than that at other pressures. NO emissions in that condition reached the maximum. Secondly, the effect of EDI timing on engine knock mitigation was examined in two engine load conditions. Experimental results showed that the LEDI was effective in suppressing engine knock and permitting more advanced spark timing. The effect of EEDI on knock suppression was less significant than that of LEDI. However, the volumetric efficiency and combustion could be effectively improved in EEDI conditions. The combined effect of spark advance and improved volumetric efficiency in EEDI conditions led to higher IMEP and engine efficiency than in LEDI conditions.