Investigation of ignition delay times for ethanol and the Brazilian gasoline

The prediction of ignition delay times is very useful during the development phase of internal combustion engines. When it comes to biofuels such as ethanol and its blends with gasoline, its importance is enhanced, especially when it comes to flex-fuel engines and the need to address current and future emissions legislations and efficiency goals. The ignition delay time measured as the angular difference between the spark discharge time, as commanded by the ECU and a relevant fraction of fuel mass burned (usually, 2, 5 or 10%). Experimental tests were performed on a downsized state-of-the-art internal combustion engine. Engine speed of 2500 rpm, with load of 6 and 13 bar IMEP were set for investigation. Stoichiometric operation and MBT or knock-limited spark timings were used, while valve overlap was varied, in order to address the effects of scavenging and residuals on ignition delay times. Results showing the effects of both are presented for both E27 (27% ethanol in gasoline) and E100 (100% hydrous ethanol). A comparison shows a general trend of reduced ignition delay times for gasoline in comparison to ethanol. However, this trend is affected by the engine running conditions. Results showing angular difference between both fuel blends are presented.