Mixture formation in gasoline direct-injection engines is largely determined by the quality of injection. Injection systems with a wide range of layouts are used today in enhancing spray quality. As parameters, the pressure and temperature of injected fuel play a crucial part in defining quality.
The effect increasing pressure has on the quality of spray is basically known. So are ways of applying this process to gasoline fuel. The effect of massively increasing the temperature of injected fuel - to the point of reaching supercritical conditions - in contrast, is not known in any detail.
For this reason, the following paper focuses attention on examining the fundamental influence of increasing fuel temperature from 25 °C to 450 °C on the spray behavior of a high-pressure injector with a GDI nozzle. Combining relevant levels of pressure and temperature, discussion also turns to supercritical fuel conditions and their effects on spray behavior.
In the course of evaluating the optical analyses conducted on the pressure chamber using the Schlieren method as well as laser diffraction spectrometry, attention centers on aspects relating to the influence of raising fuel temperature on the change in droplet size and droplet size distribution, spray angle and penetration as well as injected mass. To obtain greater understanding of the process taking place in the nozzle hole, the results obtained from 3D CFD computations are analyzed in detail.
Finally, there will be presented some results from single cylinder tests at cat heating conditions, achieved at low temperature engine conditions and heated fuel.