However, Energy Laboratory experiments in a transparent test engine show that the injected fuel may not always form a hollow cone. The tiny droplets that result are sucked into the center of the disintegrating hollow cone. The MIT research findings should help engine designers optimize the geometry of the combustion chamber to ensure complete vaporization and easy ignition under all engine conditions. As a result, much of the incoming fuel is vapor and thus easily ignited when the spark plug fires. Today's new DISI engines are designed to solve those problems.
Liquid fuel is injected directly into the combustion chamber.
By carefully designing the injector and the shape of the combustion chamber and top of the piston, designers induce flows that push the injected fuel toward the spark plug but along an indirect route that provides time for the liquid to vaporize. Several companies have now introduced DISI models, with considerable fanfare about their high efficiency and other attributes. Yet research on this emerging technology continues. At MIT, Energy Laboratory researchers led by Simone Hochgreb have been investigating basic processes that may interfere with vaporization and stratification under some conditions, with potentially serious negative impacts. Incomplete vaporization can mean incomplete combustion, unburned fuel, and high emissions of hydrocarbons and particulate matter.