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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]

• IDTs of H 2 /NC 7 H 16 mixture were measured in RCM. • A skeletal H 2 /NC 7 H 16 oxidation mechanism was developed. • Hydrogen diffusion velocity is determined by injection direction. • Hydrogen diffusion velocity influences pre-mixture homogeneity and slipping. • Hydrogen injection timing affects pre-mixture homogeneity and slipping. Achieving efficient lean combustion with homogeneous pre-mixtures is essential in marine low-speed two-stroke hydrogen/diesel engines. However, measures enhancing pre-mixture homogeneity may lead to hydrogen slipping. To address this, the numerical simulation research on injection process was carried out. A skeletal hydrogen/n-heptane oxidation mechanism with 49 species and 174 reactions was developed and validated against experimental ignition delay times in rapid compression machine with temperature range from 600 K to 800 K and pressure of 8 bar and 24 bar. Based on the mechanism, the influence of hydrogen injection parameters on pre-mixture homogeneity and hydrogen slip was investigated by three-dimensional computational fluid dynamic simulation. The angular, radial, and longitudinal velocity of hydrogen diffusion, determined by side and downward angle of hydrogen injectors directly impact the circumferential, radial, and longitudinal homogeneity of pre-mixture. By affecting swirl intensity and friction between fluid and cylinder wall, side angle indirectly influences longitudinal velocity, which dominates hydrogen slipping. Moderate side (10° − 20°) and downward (0° − 20°) angles of hydrogen injectors ensure both pre-mixture homogeneity and prevent hydrogen slipping. Finally, the influences of injection timing on pre-mixture homogeneity and hydrogen slipping were studied. An advanced injection timing (earlier than 226°CA) enhances mixing time but increases hydrogen slip risk. Conversely, delaying injection timing (later than 238°CA) prevents slipping but reduces pre-mixture homogeneity due to shorter mixing time. [ABSTRACT FROM AUTHOR]

• Ignition properties of H 2 /n-C 7 H 16 mixture was revealed by shock tube and mechanism. • H 2 /n-C 7 H 16 mixtures with more hydrogen and lower equivalence ratio have shorter IDT. • More active n-C 7 H 16 consumes before H 2 and triggers later radicals' reactions. • A skeletal hydrogen/PRF mechanism was proposed based on a skeletal PRF mechanism. In the present work, the experiments of measuring ignition delay times (IDTs) of the hydrogen/ n -heptane mixture at high temperature (1130–1485 K) and low pressure (1.25 atm) by a shock tube is implemented. The results show that mixtures with higher hydrogen proportion and lower equivalence ratio present shorter IDT. In the case of high hydrogen proportion, the n -heptane addition causes an obvious inhibition effect on the ignition of the mixture. Whereas, as the hydrogen proportion decreases, such inhibition effect weakens. As the experimental values are consistent with the predicted IDTs by NUI (National University of Ireland) mechanism, the NUI mechanism was selected to conduct the kinetic study. The consumption of n -heptane at the initial stage of reaction is earlier than that of hydrogen because the activities of n -heptane's H-abstraction and decomposition reactions are relatively high. With shock tube experimental data as the calibration basis, a skeletal hydrogen/PRF (Primary Reference Fuel) mechanism, was updated from a skeletal PRF mechanism. The skeletal hydrogen/PRF mechanism, consisting of 49 species and 162 reactions had been validated against shock tube experiment of hydrogen, n -heptane, isooctane pure fuel, PRF, and hydrogen/ n -heptane mixture. [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]