Development of a reduced multi-component combustion mechanism for a diesel/natural gas dual fuel engine by cross-reaction analysis

In this paper, a four-component reduced mechanism (methane, n-dodecane, methylcyclohexane and toluene) with 150 species and 847 reactions was proposed for predicting the combustion characteristics and emissions from natural gas-diesel dual fuel engines. Equivalence ratio (phi) from 0.5 to 2.0, pressure (P) from 30 to 90 bar, temperature (T) from 500 to 1700 K and phi from 0.5 to 2.0, P from 1 to 10 bar, T from 298 to 550 K were set as the reaction conditions for two reaction models respectively. The detailed mechanisms were reduced using the directed relation graphs (DRG), directed relation graphs with error propagation (DRGEP) and full species sensitivity analysis (FSSA) methods. The validation of the reduced mechanism was performed based on the ignition delay and the laminar flame speed data available in the literature. Then the effects of cross-reactions on the oxidation of diesel were further studied, associated with the reaction flux, concentration and sensitivity analysis. Finally, the reduced mechanisms were verified at a reactivity controlled compression ignition (RCCI) combustion mode at 25% and 75% loads, the maximum validation error is 3.3%. It was found that the effects of cross-reactions on ignition were more pronounced in medium and low temperatures. Ignition was also enhanced by an increase in the equivalence ratio, but was not found to be sensitive to pressure. Under lower temperatures, adding cross-reactions can better reveal the formation of diesel intermediates. However, at higher temperatures, the addition of cross-reactions did not significantly increase the reaction speeds of the intermediate products.

Automated summary

In this paper, a four-component reduced mechanism was proposed for predicting combustion characteristics and emissions from natural gas-diesel dual fuel engines. The validation of the reduced mechanism showed good performance under different reaction conditions. The effects of cross-reactions on ignition were more pronounced in medium and low temperatures, but not significant at high temperatures.