In this study, the chemical composition and physical properties of an alcohol-to-jet (ATJ) fuel were used to develop a surrogate mixture containing commercially available hydrocarbons. Analysis of the chemical composition of the ATJ showed a high quantity of two specific branched alkanes (2,2,4,4,6,8,8-heptamethylnonane and 2,2,4,6,6-pentamethylheptane) and a small quantity of other branched alkanes that are isomers of these two alkanes. Surrogate mixtures containing 2,2,4,4,6,8,8-heptamethylnonane and a mixture of isododecane isomers were prepared to determine what composition would match the density, viscosity, speed of sound, bulk modulus, surface tension, and flash point of ATJ. The optimal surrogate contained a 0.25 mass fraction of 2,2,4,4,6,8,8-heptamethylnonane in isododecane isomers. Combustion experiments were then conducted in a Yanmar diesel engine with fuel mixtures containing 70% (by volume) petroleum jet fuel with 30% ATJ, 2,2,4,4,6,8,8-heptamethylnonane, the optimal surrogate mixtures based on physical properties, or the isododecane isomers. The startup performances of the three 30% surrogate mixtures were very similar to that of the 70% JP-5 with 30% ATJ fuel. No significant differences were seen in the engine combustion characteristics of the three 70/30 surrogates, as compared to the base 70% JP-5/ 30% ATJ fuel mixture. These results show that a surrogate mixture has been successfully prepared that matches the physical and chemical properties and combustion behavior of an ATJ fuel.

A new Hydroprocessed Depolymerized Cellulosic Diesel (HDCD) fuel has been developed using a process which takes biomass feedstock (principally cellulosic wood) to produce a synthetic fuel that has nominally 1/2 cyclo-paraffins and 1/2 aromatic hydrocarbons in content. This HDCD fuel with a low cetane value (Derived Cetane Number from the Ignition Quality Tester, DCN = 27) was blended with naval distillate fuel (NATO symbol F-76) in various quantities and tested in order to determine how much HDCD could be blended before diesel engine operation became problematic. Blends of 20% HDCD (DCN = 45), 30%, 40% (DCN = 41) and 60% HDCD (DCN = 37) by volume were tested with conventional naval distillate fuel (DCN = 49). Engine start performance was evaluated with a conventional mechanically Direct Injected (DI) Yanmar engine and a Waukesha mechanical indirect injected (IDI) CFR diesel engine, and showed that engine start times increased steadily with increasing HDCD content. Longer start times with increasing HDCD content were the result of some engine cycles with poor combustion leading to a slower rate of engine acceleration towards rated speed. A repeating sequence of alternating cycles which combust followed by a non-combustion cycle were common during engine run-up. Additionally, steady state engine testing was also performed using both engines. HDCD has a significantly higher bulk modulus than F76 due to its very high aromatic content, and the engines showed earlier Start of Injection (SOI) timing with increasing HDCD content for equivalent operating conditions. Additionally, due to the lower DCN, the higher HDCD blends showed moderately longer Ignition Delay (IGD) with moderately shorter overall burn durations. Thus, the mid-combustion metric (CA50: 50% burn duration Crank Angle position) was only modestly affected with increasing HDCD content. Increasing HDCD content beyond 40% led to significantly longer start times.

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In this work, military jet fuel JP-5 surrogates were formulated and tested in comparison to a nominal JP-5 fuel. Combustion experiments were conducted in an advanced engine technology (AET) ignition quality tester (IQT) and a Yanmar L100W Tier 4 diesel engine due to the potential use of jet fuel in diesel engines in military situations. The surrogate development process began with determining the fuel chemical composition based on analyses of 256 JP-5 fuel samples. The physical and chemical properties of density, viscosity, flash point, surface tension, speed of sound, and distillation behavior guided the selection of the surrogate components and their composition. JP-5 differs from other aviation fuels in its properties, but most importantly in flash point, which is higher for safety purposes. Surrogates were prepared from n-dodecane, n-butylbenzene, 1-methylnaphthalene, tetralin, trans-decalin, iso-cetane, and n-butylcyclohexane as representatives of seven of the nine major chemical categories found in jet fuel. The mass fraction of each compound in the surrogates that fell within the range for that chemical class was found in real JP-5 fuels. After optimizing the surrogates for physical and chemical properties, six surrogates were selected for combustion testing in the Yanmar diesel engine, one of which was specifically selected for a low-derived cetane number (DCN). This surrogate performed poorly in the Yanmar engine. Four of the remaining five surrogates performed similarly to the baseline JP-5 in the diesel engine in terms of values and variability of ignition delay, rate of heat release, peak pressure, and the crank angle at which 50% of the fuel is burned. Of the six surrogates tested, the best one in terms of physical properties, chemical properties, and combustion behavior was the one that contained 0.2421, 0.1503, 0.0500, 0.0141, 0.0121, 0.2532, and 0.2782 mass percentages of n-dodecane, n-butylbenzene, 1-methylnaphthalene, tetralin, trans-decalin, iso-cetane, and n-butylcyclohexane, respectively.