August 15, 2009
Diesel Gas Mix for More Efficiency and Supercritical Diesel
Green bars are the engine efficiency. Conventional diesel on the left is 44% and the the best gas-diesel mix would be 53% efficient. Less heat trasfer and exhaust thermal losses.
1. What if an engine could be programmed to harvest the best properties of both diesel and gasoline fuel sources at once, on the fly, by blending the fuels within the combustion chamber? Based on tests by the University of Wisconsin-Madison engine research group would be a diesel engine that produces significantly lower pollutant emissions than conventional engines, with an average of 20 percent greater fuel efficiency as well. These dramatic results came from a novel technique Reitz describes as "fast-response fuel blending," in which an engine's fuel injection is programmed to produce the optimal gasoline-diesel mix based on real-time operating conditions.
28 page pdf presentation on "Improving Fuel Efficiency with Fuel-Reactivity-Controlled Combustion"
Under heavy-load operating conditions for a diesel truck, the fuel mix in Reitz' fueling strategy might be as high as 85 percent gasoline to 15 percent diesel; under lighter loads, the percentage of diesel would increase to a roughly 50-50 mix. 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 Reitz' strategy, just the right amount of diesel fuel injections provide the kick-start for ignition.
Reitz estimates that if all cars and trucks were to achieve the efficiency levels demonstrated in the project, it could lead to a reduction in transportation-based U.S. oil consumption by one-third.
The engine operates at much lower combustion temperatures because of the improved control — as much as 40 percent lower than conventional engines — which leads to far less energy loss from the engine through heat transfer. Second, the customized fuel preparation controls the chemistry for optimal combustion. That translates into less unburned fuel energy lost in the exhaust, and also fewer pollutant emissions being produced by the combustion process.
The best results achieved 53 percent thermal efficiency in the experimental test engine. This efficiency exceeds even the most efficient diesel engine currently in the world — a massive turbocharged two-stroke used in the maritime shipping industry, which has 50 percent thermal efficiency.
The United States consumes about 21 million barrels of oil per day, about 65 percent (13.5 million barrels) of which is used in transportation. If this new blended fuel process could convert both diesel and gasoline engines to 53 percent thermal efficiency from current levels, the nation could reduce oil consumption by 4 million barrels per day, or one-third of all oil destined for transportation.
Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. [wikipedia]
PCCI - Premixed Charge Compression Ignition PCCI patent
A dual fuel HCCI/PCCI concept is proposed by the University of Wisconson-Madison Engine Research Center (working with Sandia National Lab and Caterpillar)
-Port fuel injection of gasoline (cost effective)
-Direct injection of diesel fuel (moderate injection pressure)
-Possibility of traditional diesel or SI (with spark plug) operation retained for full load operation
• PCCI operation at 6, 9, and 11 bar net IMEP was achieved with near zero NOx and soot and a reasonable PRR
• 53% indicated thermal efficiency was achieved while meeting US 2010 EPA standards in-cylinder
2. Use of Supercritical Diesel Fuel for Improved Efficiency and Reduced Emissions Researchers at Syracuse University (New York) have developed a method to prepare, inject and combust supercritical (SC) diesel fuel.
The Syracuse team expects that the implementation of their concept—which is patented—will enable:
* Near complete combustion of diesel fuel and recovery of up to 50% of the exhaust heat;
* elimination of ~80% of criteria pollutants and a significant reduction of the air thermal impact;
* downsizing (smaller combustion chambers for the same torque and power);
* minimizing the parasitic pumping of large excess air; and the elimination of after-treatment systems