Comparative evaluation of global combustion properties of alternative jet fuels

Global high temperature and low temperature combustion properties of one conventional jet fuel (JP-8) and four alternative jet fuels are examined. The global combustion characteristics of these five fuels were hypothesized a priori based on a set of four property targets used in the formulation of surrogate jet fuels in recent studies by the authors. The high temperature combustion properties were evaluated by measuring two near-limit flame behaviors: the radical index derived from extinction limits of diffusion flames, and the critical flame initiation radius in outwardly propagating premixed flames. Two fundamental flame measurements reveal that Shell SPK exhibits the strongest high temperature reactivity, whereas Sasol IPK exhibits the lowest reactivity among the tested fuels. The relative low to intermediate temperature reactivities of these five jet fuels were compared by performing oxidation reactivity experiments in a high pressure flow reactor. The oxidation reactivity profiles demonstrated that Sasol IPK has no low temperature reactivity. The remaining jet fuels demonstrated extensive reactivity between 500 to 750 K. Of interest, despite sharing similar derived cetane numbers, Shell SPK shows a more pronounced low temperature reactivity compared to HRJ Camelina. Consequently, the results in this study indicate that the proposed four property targets can be used to predict the global combustion properties of petroleum derived jet fuels and perhaps for blends with alternative jet fuels up to 50%, but further refinements appear to be needed to precisely predict the temperature dependencies of global combustion properties of alternative jet fuels containing no aromatics.