Characterization of global combustion properties with simple fuel property measurements for alternative jet fuels

Global combustion characteristics of one conventional jet fuel (JP-8) and four nonpetroleum alternative jet fuels (Shell Synthetic Paraffinic Kerosene (SPK), Sasol Iso- Paraffinic Kerosene (IPK), Hydrotreated Renewable Jet (HRJ Camelina and HRJ Tallow)) are experimentally examined. The ranking of the fully pre-vaporized global combustion characteristics of these five fuels has been hypothesized a priori based on the relative values for four fuel combustion property targets used in the formulation of surrogate jet fuel mixtures in recent studies by the authors. In order to validate a priori speculation, the pure chemical kinetic reactivities of these fuels have been compared by performing oxidation reactivity experiments in a high pressure flow reactor and fundamental flame measurements. The oxidation reactivity profile for Sasol IPK demonstrates no low temperature oxidative characteristic of the occurrence of active alkyl peroxy radical oxidation mechanisms, whereas the remaining jet fuels demonstrate extensive reactivity between 550 and 750 K. Despite sharing similar derived cetane numbers, Shell SPK shows the more pronounced low temperature reactivity compared to the other alternative jet fuels. Two fundamental flame measurements at near-limit condition, both extinction limits of diffusion flames and critical flame initiation radii of outwardly propagating premixed flames, were used to investigate differences chemical kinetic/transport coupled high temperature combustion behaviors. Strained extinction measurements identify the pronounced high reactivity of Shell SPK, whereas critical radius measurements exhibit the distinctive low reactivity of Sasol IPK. Additional analyses along with available literature measurements indicate that the proposed four fuel combustion property targets can be used to predict the relative pre-vaporized global combustion properties of the tested petroleumderived and alternative jet fuels. Finally, further detailed understanding and improvements on DCN and TSI determination methodologies, particularly for alternative jet fuels, are addressed as a prerequisite condition to better parameterizing the combustion property targets, thus improving the quantitative predictability of a provisional combustion property target (CPT) Index. The CPT index appears useful in screening the relative global combustion properties of real petroleum derived fuels, non-petroleum alternative fuels, and their mixtures.