Compression-ignition engine performance and emissions in single and dual fuelling modes with sustainable fuels

The experimental investigation in this work reports on performance and emissions in compression-ignition (CI) engines in normal (diesel fuel only) and "dual-fuel" operation. The dual-fuel mode allows a fuel of low cetane number to be used in CI engines, with "pilot" spray injection of a fuel with high cetane number in order to provide the source of ignition. Two low cetane gaseous fuels were tested, hydrogen gas and natural gas. Hydrogen dual-fuel operation generally increases NOx emissions while CO2 emissions are reduced compared with normal engine operation. Preliminary fuel map plots show thermal efficiencies remain comparable with normal engine operation. Natural gas dual-fuel operation reduces NOx and CO2 emissions while thermal efficiencies are maintained compared with normal operation. However, significantly higher unburnt hydrocarbon (HC) emissions are recorded at low and intermediate engine loads. Lower volumetric efficiency is recorded during all dual-fuel cases compared with normal engine operation, while the possibility of "hydrogen knocking" contributes to lower maximum power output. During hydrogen dual-fuel operation, water-in-RME emulsions were also tested as pilot fuels. During these test cases, NOx emissions are lowered at certain conditions compared with the neat RME pilot. This is possibly the result of charge cooling. Overall, significant optimization is needed to improve combustion efficiency at low and intermediate engine loads during dual-fuel CI engine operation.