A numerical and experimental study of dual fuel diesel engine for different injection timings

The dual-fuel technology has the potential to offer significant improvements in the CO2 emissions from light-duty compression ignition engines, and in this sense, such a concept represents a viable solution to reduce emissions from diesel engines by using natural gas as an alternative fuel. In light duty, high-speed engines, where the combustion event can be temporally shorter, the injection timing plays an important role on the performance and emissions. Following a methodology that has been proposed in previous authors' papers, this article summarizes the results of a combined numerical and experimental study on the effect of injection timing on performance and pollutant fractions of a common rail diesel engine supplied with natural gas and diesel oil. The study of dual-fuel engine carried out in this paper aims at the evaluation of the CFD potential to predict the main features of this particular technology. The experimental investigations allow the validation of the CFD modeling and, at the same time, highlight the major aspects that arise from the actual engine operation with different diesel injection advances. The fluid-dynamic calculations are extremely useful to put into evidence the key phenomena that take place during the dual-fuel operation, say the typical flame propagation throughout the premixed methane-air medium that is activated by the early self-ignition of the diesel fuel. While previous papers have discussed the effect of the NG/diesel fuel ratio, this paper focuses the attention on different conditions that have been induced by varying the injection timing at fixed brake torque and diesel amount. Actually, the start of injection timing can considerably influence the combustion development and therefore THC and NOx fractions production. Calculations making use of the fluent code have been compared with the experimental data and a comparison between full diesel and dual fuel operation has been made, in terms of performance and pollutant levels.