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Study finds hitting thermodynamic sweet spot in dilute, boosted gasoline engines has potential for fuel economy gains between 23% and 58%

A study by a team led by Dr. Dennis Assanis at the University of Michigan suggests that accessing the “thermodynamic sweet spot” in high-efficiency, dilute, boosted gasoline engines has the potential for vehicle fuel economy gains between 23% and 58%. Their paper is published in the International Journal of Engine Research.

Recent developments in ignition, boosting, and control systems have opened up new opportunities for highly dilute, high-pressure combustion regimes for gasoline engines. This study analytically explores the fundamental thermodynamics of operation in these regimes under realistic burn duration, heat loss, boosting, and friction constraints. The intent is to identify the benefits of this approach and the path to achieving optimum engine and vehicle-level fuel economy.

—Lavoie et al.

Using a simple engine/turbocharger model in GT-Power to perform a parametric study exploring the conditions for best engine efficiency, they found:

  • Best engine efficiency in the mid-dilution range, a result of the tradeoff between fluid property benefits of lean mixtures and friction benefits of higher loads.

  • Dilution with exhaust gas is nearly as effective as air dilution when compared using a ‘fuel-to-charge’ equivalence ratio defined as Φ′ ≡ Φ (1-RGF) where RGF is the total residual gas fraction.

  • Optimal brake efficiencies are obtained over a range 0.45 ≤ Φ′ ≤ 0.65 for operation up to 3 bar manifold pressure, yielding peak temperatures under 2100 K and peak pressures under 150 bar.

These conditions are intermediate between homogeneous charge compression ignition and spark-ignition regimes and are, the team noted, the subject of much research.


  • George Lavoie, Elliott Ortiz-Soto, Aristotelis Babajimopoulos, Jason B. Martz and Dennis N. Assanis (2012) Thermodynamic sweet spot for high-efficiency, dilute, boosted gasoline engines. International Journal of Engine Research doi: 10.1177/1468087412455372



If we are still improving ICEs power density after 130+ years, how far can EV batteries be improved during the next 100+ years? A 20X potential improvement would give an EV battery with about 4000 Wh/Kg. Even heavy buses, trucks, boats, tugs/ships and heavy machinery could be battery powered.


ICE has 130+ years of infrastructure investment, so it ain't going to disappear in your lifetime.

Roger Pham

If this type of hypothetical gasoline engine is not spark-ignited and not HCCI, then what is it? Perhaps plasma or corona discharge? Perhaps using the PCCI method of dual injection, with a lean homegenous-charge preformed mixture got ignited by a small injection of diesel fuel or gasoline fuel later at near TDC, with high compression ratio. The increase in efficiencies with the PCCI method by both University of Wisconsin and by Lund University, Sweden, are well documented. So what's new here?

The limitation of spark-ignition lies in the slow flame propagation with a lean mixture and even slower flame propagation with a boosted and lean mixture, and even slower combustion still if a mixture dilution with EGR instead of with air. Meanwhile, HCCI ignition is so fast even with EGR that it severely stresses the engine at higher load, with noise and harshness issue as well.


1. Not enough info - except to determine that it is Dr. Dennis Assanis' OPINION that "gasoline engines has the potential for vehicle fuel economy gains between 23% and 58%."

2. I do not see how we can use the history of the ICE (over the last 130+ years to predict EV battery improvements over the next 130+ years.

Certainly one cannot assume anaything like a 20X potential improvement.

3. The EV was born at the same time as the ECE-V.


TT....after about 3 years, the new (2013) will go 25% further and will be much cheaper. After 20 short similar cycles, i.e. in about 60 years, similar EVs could go 6000+ Km between charges with similar volume batteries. Of course 6000 Km range is not always required, so batteries will be 10 times smaller in volume and probably 10 times cheaper too. ICEVs would have disappeared decades before. Some batteries may go for years without being recharged or refueled.

That is where the (time) relationship between 130 years old ICEVs and modern BEVs has to be considered.


How do you support your claim that EV range improvement will be 25% in 3 years and your "could go" nunmber for 60 years?
We all are subject to excitements that coincide with our wishes, but without the broadest, panoramic picture before us we are all guilty of exaggeration or unfounded optimism.
The pessimists have their numbers too regarding battery disposal, carbon footprints, rare earth mineral supply, etc. The debate on these factors is helpful and the theories spawned are instructional, but conclusion-jumping is no better than sport so let's place our bets and have friendly fun with it or get some realistic tests and empirical results.


Yeah, the experts here who can engage in actual fact-based discussion are the only ones I bother reading. The fluffy, throwaway comments I just skip over.


The 25% range gain announced for the new 2013/2014 Leaf represents about an 8%/annual improvement rate for batteries and that's very close to what was expected and about what is reasonable to expect.

If the 25%/3 years or slightly under 8%/year is projected over 60 years or so, you will get storage units capable of 6000+ Wh/Kg. Nobody claims that they will be lithium units. By 2070+ the current lithium batteries may very be in museums with out current ICEs.

ICEs power density and relative efficiency has also increased at a faster rate in the last 3 years of so. However, that was not at all the case for many decades. We all know that the opposite was the rule for many many years as ICEs went from 20 hp to 400+ hp and vehicles went from 2000 lbs to 5000+ lbs and gas price went from $0.08/gal to $4+/gal.

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