Visualization of fuel sprays for stratified cold starts in Gasoline Direct Injection engines

Övrigt konferensbidrag, 2008

About 90% of the unburned hydrocarbons (UBHC) emissions from port-fuel injected gasoline engines are emitted during cold starts, before the catalyst reaches the light-off temperature. In Gasoline Direct Injection engines cold starts can be made much cleaner by using modern fuel injectors operating at high fuel pressures and injecting the fuel late during the compression stroke to deliver a stratified charge, thereby enhancing the fuel’s rate of evaporation and reducing wall wetting. The objective of this study was to assess the relative importance of variables that influence the formation and characteristics of the sprays generated in such conditions. For this, a high-speed camera was used to acquire images and measure sprays of fuel injected by an outward-opening piezo-actuated injector into a pressurized spray chamber in which the fuel temperature could be cooled to temperatures as low as 243 K (-30 ºC). The varied parameters were fuel pressure, back-pressure, injection strategy and fuel temperature. For reliable ignition of such sprays a spark plug should be positioned in the vortex they create. The results show that if the fuel pressure is reduced to 5 MPa from the injector’s design pressure of 20 MPa, as it could potentially be during a cold start, the vortex is not created and fuel will not be present at the spark. However, multiple injections and the temperature of the fuel were found to have relatively weak effects on the vortex formation.