Experimental study of autoignition characteristics of Jet-A surrogates and their validation in a motored engine and a constant-volume combustion chamber

Abstract

The current study presents an experimental validation of jet aviation fuel surrogates formulated using a surrogate model-optimizer. Two surrogate fuel mixtures are used to emulate a practical Jet-A (POSF 4658) considering a series of physical and chemical processes in diesel engines. The surrogate mixtures consist of: n-dodecane/isocetane/methylcyclohexane (MCH)/toluene 0.3844/0.1484/0.2336/0.2336 on a molar basis (referred to as UM I), and n-dodecane/isocetane/decalin/toluene 0.2897/0.1424/0.3188/0.2491 on a molar basis (referred to as UM II). In the present study, a modified Cooperative Fuels Research (CFR) Octane Rating engine and an optically accessible, constant-volume spray combustion chamber are employed to investigate how the chemical and physical properties of these jet fuel surrogate mixtures affect the fundamental ignition behavior as compared to the targeted full boiling range Jet-A fuel (POSF 4658). The observations of ignition behavior include critical compression ratio and critical equivalence ratio, and % low temperature heat release, which are assessed using the motored engine (CFR), while physical and chemical ignition delays are measured using a modified Cetane Rating (CID 510) instrument under a wide range of air temperatures and oxygen dilution levels.The measured derived cetane number (DCN) for UM I shows a reasonably good match with the practical Jet-A fuel (POSF 4658), while gas-phase oxidation behavior is less, well-matched in the modified CFR engine. In contrast, although the measured DCN of UM II revealed a lower value than the estimated value using a surrogate optimizer, the ignition behavior is relatively well match with that of the target Jet-A in the modified CFR engine. The similarities in physical and chemical ignition delays as compared with the target Jet-A support the effectiveness of the UM II surrogate, while in contrast, the UM I surrogate only matched the chemical ignition delay. This is attributed to the importance of the surrogate component decalin, which improved the physical properties as compared to MCH, while the other three components were the same for the two surrogates.