Spray Characterization and Ignition Delay Measurements of JP-8 and IPK in a Constant-Pressure Flow Chamber

This research compares the spray development and combustion characteristics of jet propellant 8 (JP-8) and iso-paraffinic kerosene (IPK) through a range of diesel engine in-cylinder operating conditions. Non-reacting spray experiments were performed in a constant-pressure flow chamber with 99% nitrogen gas composition at constant temperature (900 K) and densities ranging from 11-56 kg/m³. Near-simultaneous, high-speed Mie and schlieren images of the spray were acquired to measure the liquid and vapor penetration lengths of the non-reacting jet. Reacting experiments, consisting of photodiode measurements and intensified high-speed movies of OH^* chemiluminescence, were performed at the same thermodynamic conditions as the non-reacting experiments, except with a 21%/79% oxygen/nitrogen ambient gas composition. Measurements of the rate of injection, issued from a single-hole axial common-rail fuel injector, showed negligible differences between the fuels. The non-reacting liquid length of IPK was approximately 20% shorter than JP-8 for the range of tested conditions, which was consistent with the average difference in volatility between the fuels. The ignition delay, determined from the photodiode record, was up to 80% longer for IPK fuel at low density conditions. Additionally, the lift-off length of IPK was measured to be approximately 50% more sensitive to ambient pressure than JP-8. These results provide fundamental information for the calibration and optimization of military diesel engines operating on conventional and alternatively sourced jet fuels.