Assessment of JP-8 and DF-2 Evaporation Rate and Cetane Number Differences on a Military Diesel Engine 2006-01-1549

The U.S. Army utilizes both world wide available diesel fuel and jet fuel (JP-8) for ground mobility applications and must maintain such fuel flexibility in order to meet mission requirements. Understanding of combustion system sensitivity to JP-8 is not well documented for such vehicle applications and thus the current knowledge base on standard diesel spray combustion must be extrapolated in order to assess fuel effects on military combustion systems. In particular, the liquid length of developed, high pressure fuel sprays is a key combustion affecting parameter that is sensitive to fuel type, the fuel delivery system, and combustion chamber thermodynamic condition. This parameter provides targeting information that is employed for assessing bulk jet mixing, cylinder pressure rise (evaporation rate), jet-wall interaction, and the formation of nitrous oxide and particulate matter.

For practical fuels it is difficult to analytically assess physical properties necessary to predict liquid length and thus well understood pure hydrocarbon fuels must act as surrogates. Typically, handbooks of such surrogate fuel thermodynamic properties are referenced to determine temperature and pressure dependence through use of an electronic library. One alternative approach to such libraries involves accurately producing curve fits of all necessary thermodynamic properties such as fuel compressibility, heat of vaporization, and density. This submission outlines such a procedure for three potential heavy hydrocarbon fuel surrogates - dodecane, tetradecane, and cetane - through utilization of a previously published liquid length model and comparison to experimental data from various sources. The overall intent of this effort is to predict JP-8 liquid length and spray penetration in a particular military diesel engine application for assessing potential fuel-based rate of pressure rise rate issues partially through the development of a general strategy for determining evaporation surrogates for fuels similar to JP-8 and DF-2 based on a mass weighted boiling point scheme. This approach is demonstrated for three fuels - heptamethylnonane (HMN), tetradecane, and a HMN-hexadecane blend - and extrapolated for predicting JP-8 liquid length.