Dual Fuel Compression Ignition Combustion Concept for Gasoline and Diesel

Dual Fuel concepts are of interest from different perspectives: use of available fuel, independence of supplier, emission reduction and energy costs. This article presents the results of experimental work investigating the possible combination and functional effects of gasoline and diesel fuels. The test bed setup for a single cylinder research engine with a displacement of 2 liters allows gasoline to be added by external mixture formation and combustion to be started by diesel pilot injection.
The goal is to reduce the engine out pollutant emissions, while keeping the efficiency at a level comparable to a modern diesel engine. The main focus is on reducing soot and nitric oxide emissions. The charge composition of gasoline is homogenous, so the combustion system can also be seen as a partial or fully homogenous combustion concept, depending on the ignition timing and the ignition delay of the diesel fuel.
Reaching the nitric oxide level of 0.4 g/kWh (Tier IV final 130-560kW) requires low combustion temperatures. Particle mass is limited to 0.02 g/kWh. A cold combustion concept on the single cylinder research engine can be realized by using exhaust gas recirculation (EGR). Soot and nitric oxide target values for Tier IV final can be achieved at engine out. The mass fraction burned 50% (MFB50) can be controlled more easily than with other concepts such as HCCI (homogenous charge compression ignition). A pilot injection system is used, which is timed close to TDC. In this study, an EGR rate of 30-35% is needed to fulfill the soot and nitric oxide requirements. The application of a lower EGR rate is possible, but the target value for nitric oxide of Tier IV final cannot be achieved. While keeping the engine out nitric oxide and particle mass inside the limits of Tier IV final, the current configuration produces a maximum indicated mean effective pressure (IMEP) of 18. A parameter study was done to better understand and optimize the combustion concept. Various parameters were adjusted, such as compression ratio, EGR rate, pilot injection quantity and timing, fuel mass fraction levels, excess air ratio and rail pressure.