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The new technology was tested on a Caterpilllar heavy duty diesel engine. It achieved a thermal efficiency of 53 percent much better than the most efficient auto diesel engines (about 45 percent) and better even than the most efficient diesel engine in the world -- a turbocharged maritime engine that is 50 percent efficient.  (Source: Caterpillar Equipment)

The new engine could cut U.S. oil consumption by 4 million barrels a day -- roughly the amount that the U.S. imports from the volatile Persian Gulf.  (Source: Flickr)
New engine could get better gas mileage than mild hybrids even

Diesel and gasoline are both great fuels from a chemical standpoint, each with its own unique advantages.  Diesel burns more completely, lubricates the engine better, produces less carbon monoxide, and is safer as it does not produce as much flammable vapors.  However it has its disadvantages -- older engines can have a greater danger of incomplete combustion, overall engine power is a bit lower, and diesel engines weigh more.

Gasoline on the other hand burns faster and produces more power (due to the faster burn, not the energetic content).  However, it also typically yields worse gas mileage than diesel, combusts less completely (in well-maintained engines), usually requires a spark to ignite, and produces more pollutants and flammable vapors.

Researchers at the University of Wisconsin-Madison, led by Professor Rolf Reitz have come up with an innovative solution -- an engine which blends diesel and gasoline fuels to get the best of both worlds.  They have designed an engine which they say will be 20 percent more efficient than traditional gas engines, while also lowering the emissions.  The new engine works via a technique called "fast-response fuel blending", which means that the engine mixes the diesel and gas to the perfect ratio for the current conditions.

Heavy loads (like that of commercial trucks) would warrant a 85 percent gasoline to 15 percent diesel mix, while light loads would typically induce a roughly 50-50 mix.  Normally the gas wouldn't combust in a diesel engine, but by adding just the right amount of diesel fuel, combustion is achieved.  In fact, the special mix lowers engine temperatures by as much as 40 percent drastically reducing the amount of energy lost to waste heat.  This allows the diesel engine to use cheaper low-pressure injection (typically in gas engines only), and burns the fuel more cleanly, producing less pollutants.

The researchers estimate that if all cars and trucks in the nation adopted the new engine, it would cut U.S. oil consumption by a third -- by 4 million barrels per day.  States Professor Reitz, "That's roughly the amount that we import from the Persian Gulf."

The engine was developed using theoretical models, then built using a Caterpillar heavy-duty diesel engine as a base.  The new engine achieved 53 percent thermal efficiency, an admirable result, considering the best diesel engine -- a massive turbocharged two-stroke used in the maritime shipping industry -- gets 50 percent.

Professor Reitz concludes, "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 one major downside is that the engine necessitates a second tank.  However, in order to meet EPA nitrous oxide emission regulations the only alternative for large diesel vehicles would be urea injection -- which would likely be more expensive, less efficient, and still require a second tank.  While there's no telling how soon the engine will start popping up in cars and trucks, it appears to be the best solution yet and the best alternative to mild hybrids.  Of course it could be combined with hybrid electric technologies for even great fuel efficiencies.



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RE: Laws of Thermodynamics?
By jawqn8 on 8/4/2009 10:05:12 AM , Rating: 5
You are both correct and incorrect. The Carnot cycle efficiency is calculated between the two operating temperatures. The Temperature that the engine burns the fuel at is called Th and the temperature that the engine rejects heat, or the outside air, is called Tc. Th is the hot temperature and Tc is the cold temperature. The equation is then Efficiency=1-(Tc/Th). That will give you the effiecency of the Carnot cycle. The temperature that you use will have to be in Kelvin to get the correct answer.

If you assume that the temperature outside is 70 degrees F and the gasoling burns at 1500 degrees F. The maximum efficiency that they engine can achieve would be 73%. The Carnot cycle uses the two temperature extremes to calculate efficiency. If you run the math for the same operating temperature but a lower environment temperature than your efficiency should increase because there is a larger difference in temperature. For example, if the temperature outside is 0 degrees F and the gasoline still burns at 1500 degrees F the efficiency is now calculated to be 75%.


RE: Laws of Thermodynamics?
By mars2k on 8/4/2009 11:08:13 AM , Rating: 2
Thanks for the info. Keep it up


RE: Laws of Thermodynamics?
By Jimbo1234 on 8/4/2009 2:10:43 PM , Rating: 2
quote:
The temperature that you use will have to be in Kelvin to get the correct answer.


You can also use the Rankine temperature scale. It's a less messy conversion from F (just add 459).

Rolf Reitz was my class selection advisor when I was getting my ME degree at the UW. Small world.


RE: Laws of Thermodynamics?
By Keeir on 8/4/2009 3:53:52 PM , Rating: 2
In further answer

A Carnot Cycle is the maximum efficiency cycle for any heat engine.

However, there are numerous types of cycles. Otto, Atkinson, Diesel, etc.

Given they started with a Diesel Engine, I think this is a modified Diesel Cycle. Probably raising the flame temperature while maintaining higher compression ratio.


RE: Laws of Thermodynamics?
By Fritzr on 8/4/2009 6:16:41 PM , Rating: 2
Carnot cycle is a pure heat transfer engine. This cycle is used today with a slight addition to the original design. Google "Sterling Cycle Engine"

More importantly the thinking that led to the Heat Powered engine is Carnot's research into the energy cycle. He proved that the maximum amount of energy available is 100% of the input energy and that the actual output was equal to input-(losses+inefficiencies).


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