Effect of Fuel Properties on Spray Development from a Multi-Hole DISI Engine Injector 2007-01-4032
Extensive literature exists on spray development, mixing and combustion regarding engine modeling and diagnostics using single-component and model fuels. However, often the variation in data between different fuels, particularly relating to spray development and its effect on combustion, is neglected or overlooked. By injecting into a quiescent chamber, this work quantifies the differences in spray development from a multi-hole direct-injection spark-ignition engine injector for two single-component fuels (iso-octane and n-pentane), a non-fluorescing multi-component model fuel which may be used for in-cylinder Laser Induced Fluorescence experiments, and several grades of pump gasoline (with and without additives). High-speed recordings of the sprays were made for a range of fuel temperatures and gas pressures. It is shown that a fuel temperature above that of the lowest boiling point fraction of the tested fuel at the given gas pressure causes a convergence of the spray plumes. Increasing the fuel temperature increases this convergence, whilst an associated increased rate of evaporation tends to reduce the penetration of individual plumes. The convergence increases gradually with increasing fuel temperature until all plumes combine to form a single wider plume with a penetration rate greater than that of the individual plumes. When all plumes are converged to form a single plume along a central axis to all the plumes, any further increase in fuel temperature at the given gas pressure acts to increase the rate of evaporation of the fuel. At experiments up to 180 °C fuel temperature and down to 0.3 bar absolute gas pressure, none of the tested fuels were found to spontaneously vaporize; all observed spray formations being a gradual evolution. Increasing the gas pressure at any given fuel temperature, leads to an increase in the boiling temperature of all components of that fuel and, hence, diminishes these effects.