Derived Cetane Number As Chemical Potential Indicator for Near-Limit Combustion Behaviors in Gas Turbine Applications

The objective of this paper is to elucidate the recently observed strong correlation between derived cetane number (DCN) and lean blow out (LBO) characteristics for both petroleum-derived and alternative jet fuels, as well as their blends. In order to evaluate the variability of fuel physical and chemical properties for petroleum-derived jet fuels, the fuel property database appearing in the DSIC-PQIS 2013 report are rigorously analyzed and compared against fuel-specific data for 17 petroleum-derived and alternative jet fuels and their blends obtained previously in our works. The global combustion characteristics of each fuel for fuel/air mixture were characterized experimentally by determining their combustion property targets (CPTs) — the hydrogen to carbon molar ratio (H/C ratio), the derived cetane number (DCN), the average molecular weight (MW), and surrogate fuel mixtures and threshold sooting index (TSI). Surrogate mixtures of known hydrocarbon species were blended to match the CPTs of target real fuel. The known chemical functional group distributions of the surrogate mixtures for each fuel or fuel blend were then used to predict well-known fundamental combustion behaviors — reflected shock ignition delay times and laminar flame speeds — through quantitative structure-property relationship (QSPR) regression analyses developed from a validation base of single component, binary and ternary mixture database. The results show that the DCN is capable of representing ignition propensity and flame propagating characteristics for both petroleum-derived and alternative jet fuels as well as their mixtures with high fidelity. Finally, the chemical functional group distributions of the real fuels themselves were directly measured using 1H nuclear magnetic resonance (NMR) spectra results. QSPR predictions based upon the experimental NMR functional group measurements are shown to provide a rapid, small sample, characterization tool for predicting the above global combustion behaviors of petroleum derived and alternative jet fuel candidates as well as their blends. Through combustor as well as stirred reactor experiments, fuel DCN has been identified as having major influence on LBO in devices that are sensitive to fuel chemical properties.