Is the future for cars and trucks a hybrid fuel engine?

Physics Today : An engine which blends diesel and gasoline fuels could potentially be 20% more efficient than traditional gas engines, while also lowering the emissions, say researchers at the University of Wisconsin–Madison .The new “hybrid fuel” engine—based on a modified diesel engine from a Caterpillar truck—works via a technique called “fast-response fuel blending,” in which the engine’s fuel injection mixes the diesel and gas to the perfect ratio for the current combustion conditions.A fully loaded truck may have a fuel mix of 85% gasoline to 15% diesel; under lighter loads, the percentage of diesel would increase to approximately 50–50.Normally this type of blend wouldn’t ignite in a diesel engine, because gasoline is less reactive than diesel and burns less easily. But in the hybrid fuel engine, just the right amount of diesel is injected to kick-start ignition."You can think of the diesel spray as a collection of liquid spark plugs, essentially, that ignite the gasoline,” says Rolf Reitz , head of the research group.This technique has two efficiency and one cost advantage, says Reitz. First, the engine operates at much lower combustion temperatures because of the improved control—as much as 40% lower than conventional engines—which leads to far less energy loss from the engine through heat transfer. Second, because of the burn optimization in the combustion chamber, there is less unburned fuel energy lost in the exhaust, which in turn produces fewer pollutant emissions. Third, the engine can use relatively inexpensive low-pressure fuel injection (commonly used in gasoline engines), instead of more expensive high-pressure injection required by conventional diesel engines.Reitz’s experiments show that the prototype is now the world’s most efficient diesel-type engine in the world, with a 53% thermal efficiency, better even than a massive turbocharged two-stroke used in the maritime shipping industry, which has 50% thermal efficiency.Thermal efficiency is defined by the percentage of fuel that is actually devoted to powering the engine, rather than being lost in heat transfer, exhaust, or other variables."For a small engine to even approach these massive engine efficiencies is remarkable,” Reitz says. “Even more striking, the blending strategy could also be applied to automotive gasoline engines, which usually average a much lower 25 percent thermal efficiency. Here, the potential for fuel economy improvement would even be larger than in diesel truck engines.” Reitz adds that they are already meeting the Environmental Protection Agency’s 2010 emissions regulations with the prototype without the addition of expensive additions, such as the urea-injection catalytic reduction used in Mercedes diesel cars and trucks, for example.The only downside would be the need to have two separate fuel tanks in the truck or car.The work is funded by Department Of Energy and the College of Engineering Diesel Emissions Reduction Consortium , which includes 24 industry partners.Reitz presented his findings today at the DOE’s 15th Directions in Engine-Efficiency and Emissions Research Conference in Detroit, Michigan.