The Relative Importance of Fuel Oxidation Chemistry and Physical Properties to Spray Ignition

The ignition delay time for direct injection compression ignition engines is determined by complex physical and chemical phenomena that prepare the injected liquid fuel for gas phase ignition. In this work, Computational Fluid Dynamics (CFD) simulations of a reacting spray within a constant volume spray chamber are conducted to investigate the relative importance of liquid fuel physical properties and oxidation chemistry on the ignition delay time. The simulations use multi-component surrogates that emulate the physical and chemical properties of petroleum-derived (Jet-A) and natural-gas-derived (S-8) jet fuels. Results from numerical experiments isolating the fuel physical property and chemistry effects show that fuel chemistry is significantly more important to ignition delay than fuel physical properties under the conditions studied. In addition, as the air charge temperature increases, the effects of physical properties and oxidation chemistry decrease, indicating that the effect of variation in fuel properties on ignition timing may be mitigated through increased pre-ignition charge temperatures.