The autoignition characteristics of conventional jet fuels (category A) and alternative fuels with targeted properties (category C) are investigated using a rapid compression machine and the direct test chamber charge preparation approach. The category C fuels were purposefully built to anticipate special property variations that generally occur in alternative fuels. Ignition delay measurements were made to examine the effects of these unique fuels at low compressed temperatures (625 K ≤ Tc ≤ 735 K), a compressed pressure of Pc = 20 bar and equivalence ratios of  = 0.25, 0.5 and 1.0 in synthetic dry air. Chemical makeup of the fuel shows insight into the effect of the amount of branching in isoalkanes and aromatic influences on autoignition. The results show noteworthy variability in the ignition properties at these low temperature and lean conditions. This variability may impact combustion performance when the engine is running outside the normal operational map or for new engine architectures in the future.

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Ignition delay of category A and C alternative aviation fuels have been investigated using a rapid compression machine (RCM). Newly introduced alternative jet fuels are not yet comprehensively understood in their combustion characteristics. Two of the category C fuels that will be primarily investigated in this study are Amyris Farnesane and Gevo Jet Fuel Blend. Amyris direct sugar to hydrocarbon (DSHC) fuel (POSF 10370) come from direct fermentation of bio feedstock sugar. Amyris DSHC is mainly composed of 2,6,10-trymethly dodecane, or farnesane. Gevo jet blend stock fuel is alcohol to jet (ATJ) fuel (POSF 10262) produced from bio derived butanol. Gevo jet blend stock is composed with iso-dodecane and iso-cetane, and has significantly low derived cetane number of 15. The experimental results are compared to combustion characteristics of conventional jet A fuels, including JP-8. Ignition delay, the important factor of auto ignition characteristic, is evaluated from pressure trace measured from the RCM at University of Illinois, Urbana-Champaign. The measurements are made at compressed pressure 20bar, intermediate and low compressed temperature, and equivalence ratio of unity and below. Direct test chamber charge method is used due to its reliable reproducibility of results. Compared to category A fuels, different combustion characteristics has been observed from category C fuels due to their irregular chemical composition.