Chemical kinetic analysis on the auto-ignition characteristics of natural gas–diesel dual-fuel combustion under engine-relevant conditions

With the advent of energy crisis and stringent emission regulations, natural gas (NG)/diesel dual-fuel engines have entered the popular view. In this paper, the accurate boundary conditions are determined by the Converge model and the transient parameters were introduced into the chemical kinetics model to make the operating conditions more closely match the actual engine operating conditions. The effects of different methane/n-heptane ratios, initial temperatures, initial pressures, and equivalence ratios on the IDT of methane/n-heptane fuel mixtures were analyzed using comprehensive chemical kinetic tools such as mole fraction analysis, ROP analysis, and sensitivity analysis. The IDT of methane/n-heptane mixture decreased significantly with increasing the equivalence ratio, initial pressure, and the proportion of n-heptane in the mixture, but the change of temperature was more complicated for the IDT. The NTC behavior of methane/n-heptane mixture was also affected by the NTC behavior of n-heptane. With the increase of initial temperature, the consumption of methane and n-heptane appeared to be significantly accelerated. The peak of radicals and intermediate groups appeared earliest and had the highest radical concentration when the n-heptane content was 30%. With the increase of initial pressure, the peak moments of the six radicals were further advanced, but the mole concentrations of O, OH, H radicals decreased significantly. This paper not only provides a reference for the design of NG/diesel dual-fuel engines, but also provides a theoretical basis and data support for improving the ignition and initial condition setting strategies of the engines.