Numerical simulation of the ZND detonation structure of mixtures of n-heptane, oxygen and diluent detonations was performed with detailed chemistry. Results show that low- temperature chemistry is activated behind high Mach number shock waves with increasing dilutions of CO2, which leads to non-monotonous thermicity profiles with two stages of energy release, caused by low- and high-temperature chemistries, respectively. For the evolution of the induction length and cell size, although the total length scales do not show negative response with increasing temperature, the length scale of the first-stage ignition demonstrates negative response when the post-shock temperature decreases within the NTC (negative temperature coefficient) regime.