A Theoretical Study on Cool Flame Oxidation as an Effective Way for Fuel Reforming: Emphasis on Ignition Characteristics and Chemical Analysis

摘要

Cool flame oxidation of hydrocarbon fuels produces substantial intermediates with various levels of chemical reactivity, which can be used for combustion control of advanced engines with low-temperature combustion. Previous investigation has evaluated the performance of low-temperature reforming under high fuel-rich conditions, whereas the potential of a broader scope of reforming conditions (especially fuel-lean scenarios) is not clear. In this work, cool flame oxidation as a reforming way was proposed to investigate the effect of reforming products from various reforming conditions on ignition characteristics of typical operating conditions, and the role of the reforming products from typical reforming conditions on ignition characteristics of different operating conditions was clarified under engine-relevant conditions. The results show that the reforming products via cool flame oxidation are more sensitive to reforming temperature than pressure and equivalence ratio. Residence time also plays an important role in reforming products, and depending on the oxidation degree, two kinds of reforming products can be identified, i.e. mild reforming and severe reforming, manifesting distinct chemical reactivity. Meanwhile, it is found that different from the previous findings of very fuel-rich reforming conditions, the ignition delay time of different blends is significantly shortened under most operating conditions, except for some scenarios (e.g. the negative temperature coefficient region) manifesting a "cross-point" behavior. Moreover, the promotion on ignition processes becomes enhanced under higher temperature, higher pressure, leaner mixture, and severe reforming conditions. Globally, cool flame oxidation as a reforming way can reduce the ignition delay time by 30 ～ 50 under engine-relevant conditions. The current work can provide new perspectives of cool flame oxidation as an effective way to control advanced engine combustion processes.