Experimental and kinetic modeling studies on the low-temperature oxidation of n-heptanol in a jet-stirred reactor

Alcohols, primarily produced from biomass, are considered promising, both as alternative fuels and as fuel additives. However, short-chain alcohols suffer from low calorific value, corrosion, and hygroscopicity. In contrast, long-chain alcohols are better candidates as their physical and chemical properties closely match diesel, enabling direct use in engines. n-Heptanol is a potential long-chain alcohol and exhibits excellent combustion characteristics and significantly low-temperature reactivity. To facilitate engine application and enhance the understanding of n-heptanol combustion, its low-temperature oxidation was investigated in a jet-stirred reactor across equivalence ratios of 0.5, 1.0, and 2.0, within the temperature range 550–880 K, at atmospheric pressure. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) identified approximately 29 oxidation species (including aldehydes, alkenes, water, etc.), and quantified their mole fraction profiles. An obvious negative temperature coefficient was observed in n-heptanol oxidation at the equivalence ratios of 0.5 and 1.0. A detailed kinetic model for n-heptanol oxidation was developed based on the Togbé model of n-hexanol oxidation. The results indicated that the proposed model can well reproduce the n-heptanol oxidation experiments. Rate of product (ROP) analysis revealed that the H-abstraction by OH radicals, forming fuel radicals, was the dominant pathway for n-heptanol consumption. Subsequently, fuel radicals predominantly underwent decomposition through the first O2-addition, H-abstraction, and bond dissociation reactions. Furthermore, this study identified the source of aldehydes and alkenes, such as heptanal, hexanal, 1-heptene, 1-hexene, etc., as products of O2-addition reactions on fuel radicals. These findings contribute significantly to a deeper understanding of the oxidative behavior of long-chain alcohol fuels.