Investigation of the combustion characteristics of a dual direct injection fuel (diesel-propane) strategy on a rapid compression expansion machine

For internal combustion engines, liquid petroleum gas (LPG) is a promising alternative fuel due to its typical specific calorific value. A rapid compression and expansion machine (RCEM) that resembles a compression ignition (CI) engine has been the subject of experimental research using a dual direct injection fuel. For this application, 10 %-100 % diesel-propane (DP) is applied based on the percentage of the low heating value (LHV) with the propane injection timing varying from 0 degrees to 40 degrees before top dead center and maintaining the diesel injection timing at 10 degrees before top dead center (BTDC). The compression ratio was varied between 17 and 19 by adjusting the connecting rod of the RCEM. The outcome indicates that at the compression ratio of 17, propane promoted no auto-ignition. Meanwhile, at a compression ratio (CR) of 19, the auto-ignition was enhanced and occurred earlier as the amount of propane increased. However, a longer ignition delay was produced as the propane fraction was above 60 %. The highest indicated thermal efficiency (ITE) was produced at a propane fraction of 40 % at 40oBTDC. At propane fractions greater than 60 %, the highest efficiency was achieved at 20 degrees 30oBTDC start of injection (SOI) of propane for both CR 17 and 19.