Effects of hydrogen peroxide addition on two-stage ignition characteristics of n-heptane/air mixtures

Abstract

Rising fuel cost and environmental concerns of greenhouse emissions have driven the development of advanced engine technology with optimal fuel strategy that can simultaneously yield high thermal efficiency and low emissions. Due to its strong reactivity and extra oxygen atom serving as an oxidizer, hydrogen peroxide (H2O2) has been used along with other hydrocarbons to promote overall combustion process. To explore the potential benefits of H2O2 in clean combustion technology, a numerical study with detailed chemistry is conducted to investigate the effects of H2O2 addition on the two-stage ignition characteristics of n-heptane/air mixtures at low-to-intermediate temperatures (below 1000 K), with due emphasis on how the negative temperature coefficient (NTC) behavior is affected. The results show that H2O2 addition shortens both the first-stage and total ignition delay times of n-heptane/air mixtures and suppresses the NTC behavior by reducing the upper turnover temperature. With increasing H2O2 addition, the lower turnover temperature, corresponding to the first-stage ignition delay minimum, is found to increase first and then decrease. Chemical kinetic analyses show that the addition of H2O2 promotes both first- and second-stage ignition reactivity by enhancing OH production through H2O2 decomposition. Furthermore, low-temperature chemistry controls the first-stage ignition, while H2O2 chemistry dominates the second-stage ignition.