Diesel used as gasoline 'spark plug' improves economy and emissions


August 11, 2009

The most fuel-efficient diesel engine in the world, the Wärtsilä RTA96C, converts 50% of fuel into power. Researchers have now achieved better efficiency with a gasoline-diesel mix

The most fuel-efficient diesel engine in the world, the Wärtsilä RTA96C, converts 50% of fuel into power. Researchers have now achieved better efficiency with a gasoline-diesel mix

The two engine technologies tend to be regarded as completely separate, so we rarely contemplate how gasoline and diesel can work together. But, in a series of tests conducted at the University of Wisconsin, scientists have used an engine’s fuel injection to produce the optimal diesel-gas mix for any given moment. The results are impressive: an average 20% greater fuel efficiency; combustion temperatures reduced by up to 40%; and effortless meeting of the stringent EPA 2010 emission regulations. Plus, the researchers believe that if their findings were implemented into every gasoline and diesel engine in the US, the savings could be as great as 4 million barrels of oil daily.

Because it’s less reactive and won’t burn so easily, gasoline could normally never fuel a diesel engine. However, the fuel-injected diesel becomes a kind of liquid spark plug, providing a kick-start for ignition. The fuel mix varies depending on circumstance: a heavily-laden truck might require a mix as high as 85% gasoline to 15% diesel, while a light load would require a roughly 50-50 blend. 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, determines the correct mix.

While the theory was initially computer-modeled, researchers put it to the test using a heavy-duty Caterpillar diesel engine. The test confirmed two of the greatest benefits of blended fuel combustion.

First, the combustion temperatures were reduced by as much as 40%, meaning far less energy was lost from the engine through heat transfer. Second, the customized fuel mix optimized combustion, with less unburned fuel lost in the exhaust and fewer emissions. (In fact, the process easily achieves the EPA’s requirement that 90% of soot and 80% of nitrogen oxide be eliminated from diesel emissions by 2010.)

In combination, these helped the test engine achieve a best result of 53% thermal efficiency. Thermal efficiency, basically, measures the percentage of fuel converted into power, and not lost in heat transfer or exhaust. The figure of 53% mightn’t seem like a lot, but so far the most fuel-efficient diesel engine in the world can only achieve a best figure of 50%.

The very good news is that this idea is, relatively speaking, fairly easy to implement. The scientists believe it will work just as well with the low-pressure fuel injection of gasoline engines as with diesel’s high-pressure valves. And, because gasoline engines average only 25% thermal efficiency, the potential for fuel economy is even greater.

The research group estimates that, if every gasoline and diesel engine in the U.S. converted to this blended fuel process – and achieved an overall thermal efficiency of 53% - oil consumption would reduce by about 4 million barrels a day, a little under a third of today's current consumption. Little wonder the Department of Energy has its funding fingers in this pie.


I hope the FBI keeps the Arabs and the worst of the oil companies from disrupting this technology by buying people off or by sabotage. Of course, that function was performed by the Department of Energy's incompetence in prior years.


So, couple this up with the scuderi air-hybrid add-on, and slap a turbo charger on it and you could probably achieve 80% effiency...and the USA will still not produce it!


The use of an additional fuel in diesel engines (stationary, passenger vehicles and big rigs) is not new. The use of petrol is probably more palatable for the scaremongers out there than the, more common and cheaper alternative: LPG \'fumigation\' broadly used in Australia. It is also available, both in diy and workshop fitted form, in the USA and some countries in Europe. The fuel savings possibilities are considerable, but it must raise a big red flag for manufacturers and legislators/enforcers, due to \'warranty\' and taxation/classification issues, respectively. I would use it if I could!


I was going to try 25/75 gas/diesel in my vw diesel but according to this study, a 50/50 mix would be the best. I have over 500 gallons of stale gasoline from a wrecking yard that I have been collecting/saving on my farm just for experimentation! I will first try it in my Yanmar diesel tractor and later, in my VW and will report back on results

Will, the tink

Surely this isn\'t new? Still, 53% is a mighty large number :) well done chaps. With the obvious example set (as Uly posted) lpg/propane with diesel

Craig Jennings

do we need to modify the engine? or not? little bit confusing. so in the gas tank we just put 20 liters gasoline and 20 liters diesel? any suggestion? how about old engines?

Abs De Austria

So.... Here it is December, 2011 and no further word on this. Over two years. Looks like the naysayers were right: The evil twins, the DOE and Big Oil quashed this one. We\'ll probably hear some time later that \"research\" and \"experimentation\" is still being done, but that\'s all that will ever come of this simple yet effective idea. If it sounds too good to be true, it\'s too good to ever happen. Guess that\'s why they call it the Department of Energy. Want to make sure we keep using more and more of it. All the talk and posturing from the gummint about cutting back is eyewash for the public and grist for the media mill. The real players in this game, the ones who make the big money and buy the politicians make the choices.

Neil Larkins

Neil, apparently it is quite difficult to get right, but there are production units, a few major haulage companies in the UK are using Diesel Blend LPG systems to improve combustion by 10-20%.

Robert Hannent

If you run gasoline through a diesel you will destroy the engine. Gasoline detonates at compression levels well below the normal compression ratios (CR) of diesel engines. Even low octane gasoline detonates in gas engines at about 12 to 1 CR. Racing fuel for use in engines with hi CR are hi octane because it is less volatile and will But diesel engines run at 20-1 or higher and even racing gas will not work properly.

The article suggests that gas is less reactive than diesel Not true. Run diesel through a gas engine and it will produce less than 50% power and will smoke like like a house afire. It will also gum up everything in the carb or fuel injection system.

Ask any diesel mechanic. Gizmag is not powered by folks who actually work on engines; they just write about them.

Guy Macher

gasoline will not detonate if injected in the cilinder like you would do it with the diesel - it will detonate if you mix it in the intake and compress it in the cilinder . you mixed up two very different ways of engines .

Károly Hőss

Hey Guy, your examples are fairly correct for someone trying to mix the fuels in the fuel tank. The article pretty clearly states that the fuels are INJECTED into the combustion chambers. Though I'm no Diesel mechanic either (though I play one on the weekends), I pretty clearly understood the extent of the information that the fine writers at Gizmag were making.

I've known many people that use LPG injection in their Diesel engines as a 'performance' boost when towing or competing. I've never considered just running the two as a daily blend....I know plenty of people that used to run LPG in their gassers when it was cheaper. I probably could pick up a tank for my truck. Hmmm? Looks like I may have another driveway project....


Hah! That's a great idea! Controlled gasoline / diesel homogenization! Still, even though it's necessary to improve upon conventional engine technology and 'technique', the Bourke engine could have prevented all the problems we face in modern times caused by incomplete combustion for over 50 years!

David Wolfe

2014 update

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