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University of Wisconsin Researchers Investigating Dual-Fuel (Gasoline and Diesel) Partially Premixed Combustion for High-Efficiency, Ultra-Low Emission Combustion; 53% Thermal Efficiency

The dual-fuel PCCI strategy showed thermal efficiency of 53%. Source: Rolf Reitz. Click to enlarge.

Researchers at the University of Wisconsin, led by Dr. Rolf Reitz, are investigating a blended dual-fuel (gasoline and diesel) concept to extend the operating range of partially premixed charge compression ignition combustion by using the varying fuel reactivity of the charge blend, which is determined in real time.

In an invited talk given at the DEER 2009 conference in Dearborn, Michigan, Reitz described experimental results showing the dual-fuel partially premixed combustion (PPC) approach at 9-11 bar IMEP operating point (about 60% load) easily meeting US 2010 emissions standards in-cylinder while achieving thermal efficiency of 53%, compared to 45% for conventional low temperature diesel combustion (LTC).

Emissions under the dual-fuel concept, at 11 bar IMEP. The green line is the US 2010 baseline. The horizontal axis shows the percentage of gasoline in the blend. Source: Rolf Reitz. Click to enlarge.

The University of Wisconsin concept proposes the use of dual fuel tanks, with port fuel injection of gasoline and direct injection of diesel, with the in-cylinder mixing of the fuels. Mixing ratios vary based on real-time operating conditions.

(Another paper presented at DEER 2009 by Christopher Gehrke of Caterpillar described their work with a pre-blended gasoline-diesel fuel with a derived cetane of 25-26 which did not have the same level of positive results as the UW approach. “There may be some benefit in pursuing this fuel blending-type strategy...but injecting the fuels through the same nozzles may not be the way to go.”)

Low temperature combustion (LTC) strategies (MK, PCCI, HCCI) are one way researchers are looking to reduce engine-out emissions while maintaining high engine efficiency. LTC has disadvantages, however, including difficulty at high load and no direct control of combustion timing. This has lead numerous researchers to look for a hybrid between low temperature diesel combustion and homogeneous charge combustion, Reitz said.

A lot of very interesting work has been done by Shell Global Solutions lab, Dr. Kalghatgi, for example, where he argues that as long as the equivalence ratios are low enough, in other words that the combustion process fuel preparation is mixed enough so that one stays in the low emission window, one can see some interesting results.

—Rolf Reitz

Partially premixed combustion increases ignition delay to add mixing time. There are two ways to achieve this partially premixed combustion strategy: one is with high EGR rates to reduce PM formation with low combustion temperatures, the other is by exploiting the properties of fuels. Kalghatgi and his group explored both the use of low-cetane fuels and exhaust gas recirculation (SAE 2007-01-0006). Other researchers have looked at high EGR rates (Akihama et al. SAE 2001-01-0655), and optimizing fuel reactivity (Bessonette et al., SAE 2007-01-0191).

Bessonette et al. found that they were able to extend HCCI load range by varying composition: 16 bar BMEP required 27 cetane fuel, while 3 bar BMEP required 45 cetane fuel. In other words, Reitz said, at high loads, you achieve best operation with gasoline-like fuels, while at low-loads, diesel-like fuel produces the best results.

Using the proposed “fast-response fuel blending”, the fuel mix might be as high as 85% gasoline to 15% diesel under heavy loads; under lighter loads, the percentage of diesel would increase to a roughly 50-50 mix.

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.

—Rolf Reitz

The US consumes about 13.5 million barrels of oil per day in transportation. Hypothetically, if the such dual-fuel engines with 53% thermal efficiency could be applied across the entire fleet, the US could reduce its oil consumption by 4 million barrels per day—about one-third of all oil destined for transportation, Reitz said.

The work is funded by DOE and the College of Engineering Diesel Emissions Reduction Consortium, which includes 24 industry partners.




Well I'm all for an increase in efficiency but I'd like to see them try the same approach to a non-fossil fuel combination.


Before the dreamers celebrate - remember.
If it's too good to be true - it probably is not.

I'd like some independent verification.

If someone has a list of outrageous claims, add this.

Might it be true? sure, anything is possible.

Roger Pham

Actually, it's not too good to be true. The 53% is indicated thermal efficiency, before substracting the friction loss in the engine. The brake thermal efficiency would likely be lower by 10-12%, to about 47%-48% or so. See the following reference, page 24:


On this same reference, (pages 10, 22, 23) port gasoline injection is made possible by running the engine in Atkinson mode, with geometric CR of 16 and effective CR of only ~10, in order to avoid detonation of gasoline-air mixture. The low combustion temperature made possible by high EGR rate of 43%, which, in turn, necessitate turbocharging to a 1.7-2 fold boost to regain lost in power as the result of low-temp combustion and Atkinson cycle.

The effect of diesel injection is to provide ignition more rapid than possible with a spark plug that must depend on the speed of flame propagation. High EGR rate, hence low combustion temp, will significant impede flame propagation. As such, one may do away with diesel injection altogether and substitute with an electrical field-plasma type of ignitor featured in GGC many months ago, and will achieve the same result. Rapid combustion at low temps and high pressures is what being accomplished here.

Likewise, Hydrogen combustion is very rapid even with very lean mixture, much more so than gasoline combustion, and can be expected to provide greater than 50% BTE.

Henry Gibson

INNAS NOAX has a free piston hydraulically actuated hydraulic fluid pumping diesel engine. It could be modified to create compression ignition of any fuel including hydrogen. Single piston operation of a big cylinder could be highly efficient. Crankshaft friction is eliminated as is any form of rotating friction and much piston sidewall friction. Ignition timing is not critical as there is no time when ignition cannot be allowed by the hydraulic system. Degrees after dead center has no meaning as the compression stroke, except for momentum, stops at ignition even if ignition was not planned and the compression stroke not finished. This engine seems to be well suited for all fuels and for one of the cheapest low CO2 hydraulic hybrid automobiles or trucks. ..HG..


UW will also be putting out another paper on DF PCCI combustion at 2010 SAE world congress.

I dont see why dual fuel combustion would not work with biofuels.

Reed Hanson

Will S

Undoubtedly, this efficiency rating is at an optimum BSFC, which means that it won't be attained in a normal acceleration/deceleration mode of the typical ICE. It could be approached, however, in an EREV, where the engine starts up, runs at the optimum RPM until the charge completes, then shuts off. The most ideal sounds like a marine international shipping environment where the engine runs for many hours or days without requiring warmup, etc.


Could be good for buses and trucks where they are large enough to have 2 fuel tanks, and are run by professionals.

If the emissions are low, it would be great for urban buses.

I guess we end up trading simplicity for efficiency - same as with hybrids.

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