The higher reactivity of hydrocarbon fuels is necessary to match supersonic airflow in scramjet engines and micro-scale effect in micro-internal combustion engines. Tert-butyl hydroperoxide (TBHP) was selected in this study as an additive reactively enhancer to explore its capacity to intensify the auto-ignition of a typical hydrocarbon (n-heptane). Ignition delay times (IDTs) of n-heptane doped with TBHP were thus measured at engine-relevant conditions covering pressure of 20 atm, temperatures of 650 – 1250 K, and equivalence ratios of 0.5 and 1.0. A nonlinear promotion effect of TBHP on the auto-ignition of n-heptane was observed. Detonation caused by TBHP in region 2 has an impact on actual reflected shock temperature and pressure at high beginning temperatures (> 1000 K). With the addition of TBHP, the negative temperature coefficient (NTC) behavior of first-stage ignition eventually vanishes accompanied with a weakened main NTC of IDT. Analyses of exothermic reactions, reaction pathways, and species evolution indicated that the quick production of ȮH and ĊH₃ radicals from TBHP enhances the reactivity of n-heptane and affects the main exothermic reaction in the early period. This study reveals the potential of TBHP to be used in the ignition regulation of the combustion of hydrocarbon fuels and provides a methodological approach for the efficient utilization of hydrocarbon fuel in scramjet engines and micro internal combustion engines.