Effect of alternative fuels on diesel low temperature combustion

A set of experiments have been carried out in a heavy duty single cylinder engine using high EGR rates and different start of injection angles (SOI). Three different fuels (conventional diesel fuel, a diesel-ethanol mixture (e-diesel) and a Fischer-Tropsch fuel (GTL)) have been tested in order to evaluate their potential to achieve Low Temperature Combustion (LTC) conditions. Diesel and e-diesel have shown poor repeatability for the most delayed angle (4 deg aTDC) due to significant cycle-to-cycle variations. GTL has shown a heat release rate pattern typical of conventional diesel combustion for all the SOI values, while diesel and e-diesel show fully premixed combustion for delayed SOI (from 4 deg bTDC). A delay of SOI causes a decrease in the brake thermal efficiency and an increase in THC and CO emissions, the latter being more important when e-diesel is used. While late injection seems to considerably improve NOx emissions, no benefits have been obtained for diesel particles, maybe due to the low engine torque tested (which causes the soot production rate to be more significant than the oxidation rate). The low autoignition tendency together with the high volatility of ethanol makes e-diesel as a promising fuel to achieve LTC conditions while keeping acceptable fuel consumption and CO/THC emissions.