Effects of low-temperature oxidation on multi-regime detonation development

Large hydrocarbon fuels commonly used in practical engines exhibit low-temperature chemistry (LTC) and negative temperature coefficient (NTC) behavior. However, the intrinsic role of low-temperature oxidation in detonation development, which is crucial for knocking mitigation and detonation propulsion, remains not fully understood. In this study, n-heptane/air mixtures with pronounced LTC reactivity were employed to investigate autoignition and reaction wave propagation triggered by localized hotspots under conditions across the NTC region, in both planar and spherical configurations. Results demonstrate that low-temperature oxidation can interact effectively with thermal inhomogeneities, thereby facilitating detonation development under engine-relevant conditions. Non-monotonic detonation responses are observed, and as reaction progress increases, multi-regime detonation development preferentially shifts toward steeper temperature gradients, with the potential convergence into a single dominant regime. The transient combustion processes and chemical-gas dynamic interactions align well with the characteristics of autoignition-driven reaction wave propagation modes. In addition, reactive intermediates produced through low-temperature oxidation substantially accelerate detonation development, particularly under intermediate temperature gradient conditions. This work provides fundamental insights into knocking mitigation in piston engines and detonation propulsion in ramjet and scramjet engines.