An experimental fuel surrogate validation approach is proposed for a compression ignition application, and applied to validate a Jet-A POSF 4658 fuel surrogate. The approach examines the agreement of both physical and chemical properties of surrogate and target fuels during validation within a real compression-ignition engine environment during four sequential but distinct combustion phases. In-cylinder Mie Scattering measurements are applied to evaporating sprays to compare the behavior of the surrogate, its target fuel, and for reference, n-heptane. Early mixture formation and low temperature reaction behavior were investigated using 2-D broadband chemiluminescence imaging, while high temperature ignition and combustion chemistry were studied using OH chemiluminescence imaging. The optical measurements were combined with cylinder pressure-based combustion analysis, including ignition delay and premixed burn duration, to validate the global behavior of the surrogate. Engine-out UHC, NO and soot emissions were also compared at different intake conditions, injection pressures and injection strategies. The proposed approach can provide validation data for further numerical engine combustion modeling and kinetic mechanism validation.
The results show the surrogate was able to match the spray behavior, high temperature radical distribution, high temperature ignition delay, and the premixed burn duration of the target Jet-A fuel. Reasonable agreement was observed between low temperature ignition delay and radical distribution. The surrogate also captures the trend of the effects of intake conditions and injection pressure when single or double injections are used.
