Measurements of Fuel Effects on Liquid-Phase Penetration in DI Sprays
The maximum extent of liquid-phase fuel penetration into in-cylinder gases is an important parameter in compression-ignition (CI) engine design. Penetration of the fuel is needed to promote fuel-air mixing, but over-penetration of the liquid phase and impingement on the bowl wall can lead to higher emissions. This maximum liquid-phase fuel penetration, or “liquid length,” is a function of fuel properties, in-cylinder conditions, and injection characteristics.
The goal of this study was to measure and correlate the liquid lengths of fuels with wide physical property variations. The fuels were injected into a large range of in-cylinder temperature (700 to 1300 K) and density (3.6 to 59.0 kg/m3) conditions, at an injection pressure (140 MPa) that is characteristic of those provided by current high-pressure injection equipment. Liquid lengths were measured for the following nine fuels: Fischer-Tropsch diesel (FTD); biodiesel (B100); methanol (M100); a non-oxygenated, hydrocarbon gasoline (HCG); an oxygenated, reformulated gasoline (RFG); a blend of 85% methanol with 15% gasoline (M85); n-hexadecane (NHD); heptamethylnonane (HMN); and Phillips #2 reference diesel fuel (DF2).
An engineering correlation for predicting liquid lengths of arbitrary fuel blends was developed for a vaporizing fuel jet. The correlation, when applied to the complete matrix of fuels and in-cylinder conditions, has a standard deviation of 12%. The standard deviation can be reduced to 6% by applying the correlation to a subset of the test matrix more representative of conditions encountered in modern-technology CI engines.