But the hot, high-pressure environment of the combustion chamber may change that picture. Professor Hochgreb, Brad VanDerWege, and Michael Shelby have therefore been working to define the physical characteristics of the incoming fuel spray in an operating engine. A laser beam is focused through a third, small quartz window. The intensity of the fluorescence indicates the concentration of the dopant in liquid and vapor form. By creating an illuminated plane with the laser, the researchers can take photographs of the fuel's location as the engine operates.
Fuel is injected through a high-pressure, swirl fuel injector.
The injector is designed to create relatively small droplets that vaporize quickly and to give rotational movement to the fuel so it enters as a wide, hollow cone rather than a narrow, focused jet that would quickly reach the opposite wall. The results were unexpected. Each image was taken when the piston was halfway up the cylinder. But in the lower left image, taken at the same pressure but at 90 o C, the hollow-cone shape disappears. Thus, when the temperature is high or the pressure is low, the fuel spray can take on a distribution that is not what designers have in mind as they optimize their direct-injection geometry and flows.