The study of combustion characteristics for conventional and renewable Jet fuels at Low-to-intermediate temperatures in a rapid compression Machine

The combustion characteristics of jet fuels, including conventional (Jet-A1 and JP-5) and renewable (hydro-processed renewable jet, HRJ) jet fuels at low-to-intermediate temperatures were studied in a rapid compression machine (RCM). Compression pressures were varied at 10, 15, and 20 bar under a low temperature combustion regime (626 K-874 K). Fuel/oxidizer mixture conditions were created in order to investigate the auto-ignition delays responding to various equivalence ratios of 0.25 and 0.5. Longer auto-ignition delays were observed with a leaner fuel/oxidizer mixture (phi = 0.25) by as much as 79.2% as compared to the richer mixture condition (phi = 0.5). Doubling the compression pressures from 10 to 20 bar led to the reduction of the auto-ignition delays by as much as 58.8%. The negative temperature coefficient (NTC) regime was found to be strongly related to the changes in the equivalence ratio, where the NTC formation is clearly observed at lower equivalence ratio of 0.25 for all the tested fuels. In addition, the renewable jet fuel exhibited a shorter auto-ignition delay by as much as 54.5% as compared to Jet-A1 and JP-5 at equivalence ratio of 0.5. The higher hydrogen-to-carbon (H/C) ratio and lower concentration of cyclic molecules in the HRJ were among the reasons for the reactivity improvement compared to the petroleum jet fuels.