High load expansion with low emissions and the pressure rise rate by dual-fuel combustion

The combustion process using two different fuels with different reactivity is known as dual-fuel combustion. Many studies have proven that dual-fuel combustion has a positive prospect in future combustion to achieve near-zero NOx (nitrogen oxide) and soot emissions with high indicated thermal efficiency. However, it has a limitation while expanding high-load conditions because of the high mPRR (maximum in-cylinder pressure rise rate) under light-duty diesel engine. Thus, it is important to establish the operating strategy with dual-fuel combustion to achieve a low mPRR while maintaining high-efficiency and low-emission combustion in high load conditions. This study describes a detailed process of emission and the mPRR reduction under 1500 rpm/gIMEP (gross indicated mean effective pressure) at 14.5 bar. Operating parameters such as the fuel rate, diesel injection timing and EGR (exhaust gas recirculation) were changed to find the suitable point for the low emissions and mPRR. Stable combustion was possible with only a small amount of diesel injection (5% to total LHV (low heating value) of fuels) because the high compression ratio helped the ignition process. After the ignition occurred with the diesel fuel, the combustion process with stabilized propagation and auto-ignition began for the low-reactivity fuel. This process helped to reduce the mPRR and provided faster combustion, which is positive for the increase in gITE (gross indicated thermal efficiency). The result indicates that the mPRR can be less than 7 bar/deg, whereas the load condition is as high as gIMEP 14.5 bar. Lower NOx and soot emissions and higher gITE were also achieved compared to the neat diesel combustion case.