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

Abstract

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.

Exploring the Possibilities of Adjusting Gensets to NATO Requirements

“…Previous studies have proved that the use of the F-34 kerosene-type fuel causes a delay in the diesel engine ignition [12,13,14,15]. In other words, the period between the start of fuel injection and the start of combustion is prolonged.…”

From fundamental study to practical application of kerosene in compression ignition engines: An experimental and modeling review

“…Not surprisingly, other researchers such as Kim et al 85 and Rothamer and Murphy 84 used it to scale shock tube and RCM data for the ease of comparison. However, Schihl and Hoogterp-Decker 83 cautioned that τ ∝ 1 / P cannot be used for pressure scaling ignition delay times that are derived from spray combustion experiments, including those from engine experiments, as both physical and chemical ignition delays are involved. Interestingly, Balagurunathan 71 and Davidson et al 75 discovered from their shock tube experiments that under high temperature conditions, the ignition delay times of the tested kerosene fuels were shorter with leaner mixtures and longer with richer mixtures, which were contrary to those of lower temperature conditions.…”

Spray combustion of Jet-A and diesel fuels in a constant volume combustion chamber

“…Their results showed that diesel liquid penetration was the longest, followed by JP-8 and Jet-A, under 900 K ambient temperature without reaction, and there was a very small difference between JP-8 and Jet-A. Ignition delay data for jet fuel were measured in a heavy-duty diesel engine [19,20], shock tube [21,22], rapid compression machine [23] and constant volume chamber [24] by different research groups. These results showed that JP-8 had a longer overall ignition delay time than diesel.…”

“…Many experiments have been conducted in real engines or well-controlled combustion devices [18][19][20][21][22][23][24]. Simultaneous imaging of liquid spray and vapor fuel was performed by Kook and Pickett for different fuels in a constant-volume chamber under typical diesel engine in-cylinder conditions [18].…”