On the Ignition Behavior of JP-8 in Military Relevant Diesel Engines

U.S. Army ground vehicles predominately use JP-8 as the energy source for ground vehicles based on the ‘one fuel forward policy’. Though this policy was enacted almost twenty years ago, there exists little fundamental JP-8 combustion knowledge at diesel engine type boundary conditions. Nevertheless, current U.S. Army ground vehicles predominately use commercial off-the-shelf or modified commercial diesel engines as the prime mover. Unique military engines are typically utilized when commercial products do not meet the mobility and propulsion system packaging requirements of the particular ground vehicle in question. In either case, such engines have been traditionally calibrated using North American diesel fuel (DF-2) and overall engine performance degradation while operating on Jet Propellant 8 (JP-8) wasn't given much consideration since any such associated power loss due to the lower volumetric energy density was not an issue for most applications at then targeted climatic conditions. It is becoming more apparent that current and future commercial diesel engine combustion system strategies will be adversely affected by use of JP-8 in comparison to DF-2 due to combustion affecting chemical and physical property differences of ‘out laying’ global JP-8 samples that are problematic under largely premixed combustion strategies. One important example is ignition quality where the mean cetane index for JP-8 utilized by the U.S. Army during the last five years has been typically in the 43 to 44 range, but the variance has been relatively large depending on the particular supply source with worst case scenarios exhibiting values near 30. Similar variances have been observed with other key properties such as distillation and viscosity.

To date, there has been little research performed on assessing ignition behavior differences between a mean physical and chemical property JP-8 and DF-2. The objective of this submission is to study and document JP-8 autoignition characteristics under diesel engine-like thermodynamic conditions in order to provide information that might be useful in generating JP-8 ignition models. This effort includes recent ignition data from a single cylinder diesel engine, a production multi-cylinder diesel engine, a shock tube, and a constant volume bomb.