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Ignition delay times (IDTs) were measured in a shock tube facility for NH 3 /n-heptane mixtures with NH 3 concentrations in the blending fuel ranging from 0.3 to 0.95 by molar fraction. The measurements were conducted under low pressure of 2 atm and intermediate temperatures of 1350–1500 K at equivalence ratios of 0.5, 1, and 2. With the increase of n-heptane content or equivalence ratio, there is a decrease in the IDTs of NH 3 /n-heptane mixtures at intermediate temperatures. A detailed mechanism was updated in this study based on the mechanism of Dong et al. Subsequently, the proposed mechanism was compared to existing blending mechanisms of ammonia and n-heptane in terms of laminar burning velocities (LBVs), IDTs, and species profiles reported in literature. The present model improved the predictions in reproducing the performed experimental measurements compared to previous mechanisms. Finally, rate of production (ROP), sensitivity analysis, and instantaneous and cumulative reaction path analysis were performed to interpret the experiment observations and deepen the understanding of auto-ignition kinetics of ammonia and n-heptane. The results indicate that intermediate species, such as C 2 H 4 and C 3 H 6 , characterized by long lifespans and high concentrations during n-heptane decomposition, play a crucial role at elevated temperatures, while the significance of n-heptane dehydrogenation by NH 2 diminishes with increasing temperature. [ABSTRACT FROM AUTHOR]

• Influence of exhaust gases on the ignition of CH 4 /n-C 7 H 16 mixture were revealed. • Thermal, chemical and third-body collision effects are qualitatively compared. • CO 2 suppressed ignition due to its thermal and chemical effect. • H 2 O accelerated ignition due to its third-body and chemical effect. • The addition of CO 2 /H 2 O mixture slightly fastened auto-ignition of CH 4 /n-C 7 H 16. To further optimize the combustion performance of natural-gas/diesel engine under exhaust gas recirculation (EGR) condition, influence of physicochemical impacts of H 2 O and CO 2 on the ignition characteristics of n-heptane/methane mixture (Φ = 0.5/1.0) under various thermodynamic conditions (p = 2 bar/1199 K < T < 1568 K, p = 60 bar/700 K < T < 1200 K) were investigated by shock tube and NUI mechanism. Experiments indicated at p = 2 bar/1199 K < T < 1568 K, CO 2 and H 2 O additions increased and shortened ignition delay times (IDT) respectively. Mixture of CO 2 and H 2 O slightly accelerated ignition. Original and minor modified NUI mechanism well captured the inhibition and acceleration effect of CO 2 and H 2 O on ignition respectively. Both thermal and chemical effects of CO 2 (R36:CO + OH = CO2 + H) were responsible for its ignition inhibition impacts at higher temperatures. Whereas thermal effect of CO 2 became the dominant factor at lower temperatures. Chemical effect of H 2 O (H 2 + OH<=>H + H 2 O&O + H 2 O<=>2OH) promoted OH formation and enhanced whole system reactivity, which suppressed its thermal effect and accelerated ignition process. At p = 60 bar/700 K < T < 1200 K, CO 2 addition significantly retarded ignition due to its thermal effect. At 900 K < T < 1200 K, the higher third-body efficiency of H 2 O promoted ignition (R21:H 2 O 2 (+M) = 2OH(+M)&R34:H + O 2 (+M) = HO 2 (+M)). At 700 K < T < 900 K, thermal effect of H 2 O, which suppressed its third-body effect, inhibited ignition progress. These observations implied that the impact of exhaust gases on the ignition of n-heptane/methane depended on the coupled influence mechanisms of physicochemical effects, the composition of exhaust gases and located thermodynamic conditions. At intermediate-temperature high-pressure conditions (typical thermodynamic conditions of dual-fuel engine), raising the concentration of H 2 O or CO 2 in exhaust gases accelerated or delayed the combustion progress of natural-gas/diesel engine at EGR condition by enhanced third-body effect or thermal effect respectively. [ABSTRACT FROM AUTHOR]