Combustion Characteristics of Dual-Fuel Diesel Engine Using Emulsified Bio-Fuel for Pilot Ignition

Compression-ignition engines are more efficient than similar-sized spark-ignition engines because of the higher compression ratios and leaner operation. The emissions of soot and nitrogen oxides are the main hurdle in the wider exploitation of these engines. Dual-fuelling is a means favoured in solving the emission problem because high octane fuels can be used as the main fuel ignited by a smaller pilot injection of diesel fuel or another high cetane fuel. These dual-fuel engines produce lower particulate matter than diesel operation and lower nitrogen oxides than spark ignition engines, while retaining the desired compression-ignition engine efficiency. In the present investigation, tests were conducted using renewable and non-renewable fuels for pilot injection. The pilot fuels employed were conventional diesel fuel as baseline, neat and emulsified rapeseed methyl ester (RME) known as bio-diesel while natural gas was used as the main fuel. The emulsified pilot fuels were found to have extended ignition delay, compared to neat diesel and neat RME pilots, by a maximum of 10%, producing up to 30% lower peak combustion pressures. Emissions of nitrogen oxide were found to be significantly reduced (by about 40%) when emulsified fuels were used as pilot ignition at certain conditions. For the same conditions, unburnt hydrocarbons as well as carbon monoxide emissions were found to have increased (by about 60%). Carbon dioxide emissions were found to be relatively unchanged. It is noted that at high loads, all pilot fuels produced similar amounts of exhaust gas species.