The recent strict emission regulations and the necessity to reduce the global CO2 levels have promoted research studies in alternative fuel combustion technologies. Dual-fuel technology is a fascinating approach as it can combine the benefits of two fuels to achieve high thermal efficiency and lower harmful emissions. Natural gas burns cleaner than other fossil fuels, and its recent low price makes it an attractive fuel as a near-term solution. The utilization of natural gas with diesel in a compression ignition engine can result in efficiency improvement and lower CO2 emissions. However, at low engine loads, natural gas-diesel operation suffers from low combustion efficiency and high unburned hydrocarbon and carbon monoxide emissions. The present paper collates the work of experimental and simulation studies on natural gas-diesel dual-fuel operation over three different engine setups. Two single-cylinder, with and without optical access, and a multi-cylinder engine were used to analyze the effects of different diesel injection and air-path strategies on the combustion performance, with a focus on the low-load operation zone. The results show that the injection timing, as well as intake charge dilution, can severely promote clean combustion at the low-load zone. An advanced diesel injection can enhance the diesel-natural gas homogeneity within the cylinder and improve the combustion efficiency of the engine. On the other hand, high levels of exhaust gas recirculation are mandatory to suppress the NOx formation and further enhance the engine’s brake thermal efficiency.
- engine combustion
- natural gas