Combining Gasoline and Diesel for More Efficient Engines

Taken separately, gasoline and diesel fuel both bring a unique set of advantages and disadvantages to internal combustion engines. Experts at the University of Wisconsin-Madison (UWM) have therefore seen no reason why the two should not be combined in their experiments, in an attempt to harvest the best of both worlds, with as little negative effects as possible. They advocate a new type of internal combustion engine, in which the two types of fuel are mixed directly in the combustion chamber. Details of the new system were presented yesterday at the 15th US Department of Energy (DOE) Diesel Engine-Efficiency and Emissions Research Conference, held in Detroit.

According to UWM research group leader Rolf Reitz, applying the theory would result in a new, hybrid-like diesel fuel system, which would reduce emissions by about 20 percent, and would also be a lot more efficient in terms of fuel consumption. This is achieved through the use of a proprietary, new system called “fast-response fuel blending,” which mixes the fuel directly in the chamber according to the road conditions of the time. In other words, the system does not inject a constant amount of fuel, such as in regular combustion engines.

The expert's strategy also found a solution for the eternal problem that diesel and gasoline had – namely the fact that the latter did not ignite as fast as the former. He says that the solutions devised at the University move past this problem. “You can think of the diesel spray as a collection of liquid spark plugs, essentially, that ignite the gasoline. The new strategy changes the fuel properties by blending the two fuels within the combustion chamber to precisely control the combustion process, based on when and how much diesel fuel is injected,” Reitz, who is also the UWM distinguished professor of mechanical engineering, explains.

“For a small engine to even approach these massive engine efficiencies is remarkable. 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. What's more important than fuel efficiency, especially for the trucking industry, is that we are meeting the EPA's 2010 emissions regulations quite easily,” the expert adds.