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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: variable octane
By Motoman on 8/4/2009 12:35:23 PM , Rating: 4
No, especially considering that diesel doesn't really contain octane molecules. Diesel is rated by it's cetane molecule content.

RE: variable octane
By phorensic on 8/4/2009 12:46:12 PM , Rating: 2
Noted, but you could say you can control the burn rate based on the mix. I think this is probably a dream for a race car motor designer. They tend to use high octane fuels but have to compromise the design/tune of the engine around the octane. Imagine if they could have a variable octane fuel, they could probably make more power over a more broad range. I know I keep using the word octane, but do you see what I mean?

RE: variable octane
By Motoman on 8/4/2009 12:55:59 PM , Rating: 2
I see what you're getting at, but I'm not sure it works out that way...

You're going to set up the compression ratio for whatever fuel you intend to run. In some sports, there's even a spec fuel, so you don't have much doubt what fuel that's going to be.

I am not aware of any reason why you'd want to variably change the burn rate of your fuel, because then you'd be also wanting to dynamically change your compression far as I have ever heard, and I've been involved in racing for about 30 years now, there is a given compression ratio that is ideal for a given fuel, regardless of whatever else is happening. So I don't think there's an obvious reason to want to muck with the nature of your fuel during runtime.

RE: variable octane
By phorensic on 8/4/2009 1:17:43 PM , Rating: 2
There has to be some type of advantage. We have made intake and exhaust valve duration and lift completely variable, we have ignition timing *curves*, some manufacturers go through great lengths to put in variable length intake manifolds, Toyota has that VVIS tech, turbochargers now come with variable turbine blades. While injecting fuel is varied to get the right AFR, what is still static is the octane/burn rate, etc. Why not play around with that variable too?

RE: variable octane
By Motoman on 8/4/2009 1:31:24 PM , Rating: 2
I guess I don't have a scientific answer for you...just doesn't feel right to me that you'd want to mess with that. Interesting question though...I have a buddy of mine who's one of the top 2-stroke design guys in North America (he gets contracted by companies like Bombardier to do 2-stroke design work) time I talk to him I'll see what he thinks.

RE: variable octane
By Jimbo1234 on 8/4/2009 2:26:25 PM , Rating: 2
Variable turbo geometry is for a different purpose. Turbines are most effective running at a specific constant speed and drop off rapidly when you devivate from that. The vane angle determines that speed. Having a variable vane turbo allows higher efficiency over a larger speed range, therefore reducing turbo lag.

RE: variable octane
By phorensic on 8/4/2009 3:16:41 PM , Rating: 2
The same way having a variable burn rate would allow a higher efficiency over a larger RPM/load range....right? That's what I was getting at.

RE: variable octane
By Alexvrb on 8/5/2009 12:14:17 AM , Rating: 2
Lets say you've completely tuned a motor to make the most out of 93 (R+M) octane, and you've got some magical way to dynamically move from 93 to 87 and anywhere in between. When you dynamically lower the octane rating of the fuel, you have to correspondingly alter valve timing, ignition timing, compression ratio (magic), and air induction (if applicable). But then all you're really doing in the end is lowering your power output as you drop the octane rating. If only there was some other way to reduce power output... oh yeah! Reduce how much gasoline you're dumping in.

Really, there might be efficiency benefits, I don't know. But you brought up a race car engine, which implies wanting maximum performance. You build the motor to get the most out of the fuel available/allowed. If you do ANYTHING that alters the octane or combustability of the fuel downward (the only possible direction when they limit *and/or test* your fuel's content) it can only serve to reduce power. Which you can also do by backing off the accelerator.

RE: variable octane
By Spuke on 8/5/2009 1:21:56 PM , Rating: 3
But then all you're really doing in the end is lowering your power output as you drop the octane rating.
Higher octane does not provide more power, it increases knock resistance which allows more power.

RE: variable octane
By Black69ta on 8/9/2009 1:30:27 AM , Rating: 2
Agreed, the popular myth oil companies like to spread is that premium fuel makes more power in your grocery getter. They tell us this to sell more premium unleaded. In reality, Octane is only a Rating, an it measures the resistance to pre-ignition, detonation, or knocking. octane and flame speed has nothing to do with power production. Compression ratio determines the required Octane. Higher compression ratios requires higher octane ratings to avoid detonation. But, different engine designs tolerate different octanes for the same compression ratio. Not sure where I saw it but a few years ago Saab or Volvo experimented with a variable compression engine.

RE: variable octane
By JediJeb on 8/5/2009 12:11:42 PM , Rating: 2
The octane and cetane ratings are not actually based on the content of those compounds in the fuel, but how the fuel burns in relation to those compounds, including btu value and auto ignition tendency. If you run low octane fuel in an engine with too high compression the fuel ignites before the spark plug fires, causing pre-ignition which can damage the engine or lower efficency.

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