Blending Fuels to Boost Efficiency

RESEARCHERS AT THE UNIVERSITY OF WISCONSIN-MADISON SAY THAT BLENDING DIESEL FUEL WITH GASOLINE CAN IMPROVED DIESEL ENGINE FUEL EFFICIENCY by an average of 20 percent while meeting U.S. government emissions mandates without costly pollution control equipment.
While fast-response fuel blending technology would require modification of diesel engines and separate fuel tanks for diesel and gasoline, it would use fuels readily available at the pump today. Rolf Reitz, a mechanical engineer who led the research, said the technology can also be applied to gasoline engines.
If all internal combustion vehicles were converted to dual fuel engines as efficient as his most efficient prototype - 53 percent - Reitz estimates that the United States would save on-third of all petroleum used for transportation, or roughly 4 million barrels per day.
Industry is apparently listening. The Department of Energy and University of Wisconsin's Diesel Emissions Reduction Consortium, which includes 24 industry partners, are funding Reitz's research.
Fast-response fuel blending calls for mixing the two fuels inside the engine's combustion chamber. Ordinarily, gasoline does not burn in a diesel engine because it is less reactive than diesel fuel. When Reitz sprays the two fuels into the combustion chamber together, however, the diesel ignites the gasoline.
The blending technology matches the diesel-gasoline ratio to operating conditions. Under heavy loads, such as accelerating or climbing a hill, the fuel mix might go as high as 85 percent gasoline. Under lighter cruising loads, the percentage of gasoline would fall to 50 percent.
According to Reitz, the mix enables diesel engines to operate up to 40 percent cooler, which reduces energy loss through thermal transfer. Better yet, controlling the diesel-gasoline ratio not only improves burn efficiency but also reduces emissions. In fact, it enables trucks to meet particulate and nitrogen oxide emission levels mandated by the Environmental Protection Agency without buying expensive catalytic reduction or exhaust gas recirculation equipment.
Reitz used computer models to develop the blending strategy. This enabled him to run thousands of simulations and optimize his power strategies before testing the technology on a Caterpillar heavy-duty diesel engine. The tests confirmed the model's predictions. The best tests achieved 53 percent thermal efficiency, 20 percent higher than conventional diesel engines. In fact, it was higher than today's gold standard for commercial engines, the turbocharged two-stroke diesels used in maritime shipping.
"Even more striking, the blending strategy could also be applied to automotive gasoline engines, which usually average a much lower 25 percent thermal efficiency," Reitz said. " Here, the potential for fuel economy improvement would even be larger than in diesel truck engines."