Jet fuel ignition variability : constant volume spray and shock tube experiments

Abstract

Ignition delay times for conventional and alternative jet and diesel fuels of interest to the United States Department of Defense were measured in a constant volume spray combustion chamber and a shock tube in homogenous gas-phase reflected shock experiments. Experiments were performed in the spray environment for spray of fuel into hot air at 1, 2.14, and 4 MPa pressure and 620-830 K. Shock tube experiments were performed for homogenous stoichiometric fuel/air mixtures at pressures of 20, 40, and 80 atm and for 660-1310 K. These experiments characterize the relative reactivity of the fuels, the dependence of reactivity on temperature and pressure, and correlate reactivity between the spray and homogenous gas-phase environments. Important results include three observed temperature regimes in the shock tube experiments and observed increased pressure dependence in the negative-temperature-coefficient (NTC) regime in both the shock tube and spray ignition experiments. The spray experiments show decreasing temperature dependence as the temperature increases from the low-temperature regime towards the entrance of the NTC. The fuel reactivity trends measured with the derived cetane number (DCN) in the spray experiments correlate in a power law relationship with ignition delay measured in the shock tube in the NTC, indicating DCN is a measure of NTC gas-phase chemical kinetic reactivity. The experimental database reported here should be valuable for the future development of chemical kinetic models for jet and diesel fuels.