Effect of ethanol content, water injection, and compression ratio on combustion and detailed emissions in an SI-GDI engine

The transportation sector accounts for 29 % of the total greenhouse gas emissions produced in the US. Steadily tightening criteria emissions and fuel efficiency requirements have led to current research efforts evaluating multiple mixed strategies or extending beyond traditional engine architectures and fuels. Ethanol is used extensively as both a fuel additive and primary fuel replacement for gasoline. Modern engines utilizing boosting or high compression ratios require fuels such as ethanol that are more resistant to pre-ignition to operate efficiently at high load conditions. Water dilution has historically been used for knock reduction and some potential has been found for emissions and efficiency improvements. The studies on these topics, however, often focus on wide-open-throttle (WOT) conditions and neglect part load where engines normally operate. This investigation evaluates the combined effects of fuel ethanol content, compression ratio, and water dilution on the combustion and emissions characteristics A 2.4L 4-cylinder naturally aspirated (NA) gasoline direct injection (GDI) engine at part load conditions. The results indicated that the varied combinations of compression ratio and fuel ethanol content did not change the typical performance or emissions results expected for either parameter alone. Water dilution only significantly degraded stability at conditions with coefficient of variation (CoV) of indicated mean effective pressure (IMEP) values near or above 3 %. Water dilution at 10 % and 20 % W/F rations reduced average oxides of nitrogen (NOx) emissions by 20 % and 40 % respectively. The water dilution effect on unburned hydrocarbons (UHCs) was more mixed with flame ionization detector (FID) results showing mixed positive and negative effects for lower ethanol content fuels and up to a 20 % increase in UHC emissions with the high ethanol fuel (E85). Fourier transform infrared (FTIR) results agreed with the fuel blend UHC sensitivity reported with the FID. Ethanol emissions were found to increase by two to three times more for each level of water dilution than unburned gasoline emissions.