The physical properties of direct sugar to hydrocarbon diesel (DSH-76) and several binary mixtures of n-hexadecane and 2,2,4,6,6-pentamethylheptane were measured in this work. The density and viscosity were measured at temperatures ranging from (293.15 to 393.15) K, and the pure component values fell within the range of previously reported values. Speed of sound data at temperatures ranging from (293.15 to 323.15) K increased from (1089 to 1357) m•s −1 . The bulk modulus was calculated from the density and speed of sound data, and its values ranged from (858 to 1425) MPa. Flash point values ranged from (318 to 408) K, and the surface tension values ranged from (21.8 to 27.3) mN•m −1 . The values of density, viscosity, speed of sound, bulk modulus, flash point (378 K), and surface tension (25.0 mN•m −1 ) for the DSH-76 fell within the range of values measured for the binary mixtures of nhexadecane and 2,2,4,6,6-pentamethylheptane. These data suggest that a binary mixture of n-hexadecane and 2,2,4,6,6pentamethylheptane may be a suitable surrogate for renewable fuels such as DSH-76.

In this study, the chemical composition and physical properties of an algal-based hydrotreated renewable diesel (HRD) fuel were used to develop a surrogate mixture containing commercially available hydrocarbons. Analysis of the chemical composition of the algal HRD showed a small quantity of low-molecular-weight components and a high quantity of four high-molecular-weight components: n-pentadecane, n-hexadecane, n-heptadecane, and n-octadecane. Using these four components, a fifth branched component was added to match the physical properties of the algal HRD. Candidates for the fifth component were 2-methyloctane, 2-methylnonane, isooctane, and isododecane. The isooctane- and isododecane-based surrogates were tested in a Yanmar engine along with algal HRD and petroleum F76 diesel to assess the start of ignition, start of combustion, ignition delay, maximum rate of heat release, and overall combustion duration. The surrogate that best matches the physical properties of the flash point, density, viscosity, and surface tension as well as most closely reflecting the combustion metrics is one containing isododecane, n-pentadecane, n-hexadecane, n-heptadecane, and n-octadecane.

In the caption of Figure 13, "Injection delay" should be "Ignition delay".

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A vegetable oil from algae has been processed into a Hydrotreated Renewable Diesel (HRD) fuel. This HRD fuel was tested in an extensively instrumented legacy military diesel engine along with conventional Navy diesel fuel. Both fuels performed well across the speed-load range of this HMMWV engine. The high cetane value of the HRD (77 v. 43) leads to significantly shorter ignition delays with associated longer combustion durations and modestly lower peak cylinder pressures as compared to diesel fuel operation. Both brake torque and brake fuel consumption are better (5–10%) with HRD due to the cumulative IMEP effect with moderatly longer combustion durations. Carbon dioxide emmisions are considerably lower with HRD due to the improved engine efficiency as well the more advantageous hydrogen-carbon ratio of this HRD 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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