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Lund Team Shows 57% Thermodynamic Efficiency in a Gasoline-Fueled Heavy-Duty Diesel Engine Using PPC

Gross indicated efficiency (%) of Scania heavy-duty diesel running on gasoline using PPC. source: Bengt Johansson. Click to enlarge.

Researchers at Lund University in Sweden have shown a thermodynamic efficiency of 56% in a gasoline-fueled single-cylinder light-duty engine and 57% in a gasoline-fueled single-cylinder heavy-duty engine using the Partially Premixed Combustion (PPC) concept. Under higher load, they achieved 52-55% thermodynamic efficiency with 99.8% combustion efficiency and engine-out NOx below US10/Euro6 levels in the heavy-duty engine.

Prof. Bengt Johansson presented the results at the US Department of Energy’s 16th Directions in Engine-Efficiency and Emissions Research (DEER) Conference in Detroit.

Although HCCI (Homogeneous Charge Compression Ignition) was developed as a means to achieve ultra-low NOx and soot simultaneously with higher efficiencies, the viability of HCCI applications appears limited to lower load operations. Among the challenges facing HCCI combustion are acoustic noise, lack of direct control of the combustion and too diluted air-fuel mixture requirement.

Partially Premixed Combustion (PPC) was developed as a means to increase efficiency in the order of 50% or above, achieve low NOx and soot, and run the whole load range. PPC is a mix of the classic diesel combustion process and HCCI using a fully pre-mixed charge. If you consider standard diesel combustion as “black” and HCCI as “white”, Johansson said, PPC is some varying shade of gray.

PPC uses a rather early injection to create a premixed fraction of the fuel mixture, and a late injection to obtain stratification. By changing the ratio of these two injections, it is possible to tune the burn rate.

More fuel in the first injection means a faster, more HCCI-like combustion; more fuel in the second injection results in combustion more like regular diesel diffusion controlled combustion.

The Lund team worked with a Saab variable compression ratio engine, a GM L850 world engine, and the Scania heavy-duty diesel engine. As a baseline, they found that running the GM engine in spark ignition (SI) mode at a compression ratio of 9.5:1 (standard) at low load resulted in a thermodynamic efficiency of about 30%. Boosting the compression ratio to 18:1 resulted in thermodynamic efficiencies in the range of 30-40%. Switching combustion mode from normal flame propagation to HCCI resulted in roughly 50% thermodynamic efficiency across the three engine platforms, Johansson said.

We can also see all three engines would have about the same thermodynamic efficiency. There is no major difference...We can also see that HCCI kind of stops at about 6 bar BMEP. We did 20 bar HCCI, but I would not recommend it...There is actually a [combustion efficiency] penalty going from SI to HCCI. People saying that HCCI is an efficient combustion process, I wouldn’t really say so because you lose 10% of the fuel.

—Bengt Johansson

When using a diesel (compression ignition) engine running with diesel fuel, the load region in which the engine can run in PPC mode is limited to 5-6 bar gross IMEP, noted Vittorio Manente from Lund in his PhD thesis on the subject. Increasing the upper load PPC boundary in a diesel engine could thus either require a piston with much lower compression ratio has in conjunction with “an intolerable amount of EGR” to keep the start of combustion and the end of injection separated; or a fuel that is more resistant to auto ignition needs to be used: e.g., low-cetane diesel or gasoline.

The Lund team used regular US gasoline in their engines.




Very promising.


This could eventually make an improved genset for PHEVs of all sizes if it is scalable. The fuel saving could be substantial.


Yup, I'm thinking genset too. 56% is the best thermal efficiency for any ICE we've seen on GCC, isn't it?



that bring us to the discussion I had with Roger Pham here...why don't we developp gazoline powered diesel, that was my question? right. Here is the answer Partialy Premixed Combustion, 57% efficiency is outstanding even a fuel cell can't do that.

If their result is confirm you can expect to see many gazoline powered diesel in the road of US in a near future, with Sedan size car hitting 50MPG without hybrid drivetrain


Interesting...looks like PCCI is becoming preferred over HCCI.

The Goracle

"Boosting the compression ratio to 18:1 resulted in thermodynamic efficiencies in the range of 30-40%"

So we went from gas engine efficiency to diesel engine efficiency. See your undergrad thermodynamics text for the equation showing this.

Now, why not run the compression from 18:1 to 36:1, using diesel fuel, with PPC, achieving 70% efficiency?

This is certainly bad news for the coal burning electric cars. Especially given their limited range problem.


Yes, this is good technically for an ancient engine technology. Granted efficiency imporvement helps lower total consumption. But we still have to PAY for the fuel. We still need to import the oil and refine it somewhere. We still need to PAY to defend nations that produce the oil. The contemporary petroleum economy delivers FEW jobs to N. Americans.

If we build new nuclear/solar/wind/geotherm and convert old coal to NG AND instill a national residential CHP project - we would cut petroleum addiction in half. Replacing the ICE with electric motors may be painful for engineers married to combustion - but it's a century OLD already. Time for some new stuff.

But sure. Build a 1 liter PPC engine for gensets to help the electric transition.



This doesn't end electric cars, it bridges us to them by way of PHEV. If your genset is 50% efficient, your Chevy Volt styled range extended electric vehicle adds the benefit of regenerative braking, clean operation from a standing start, and allowing the genset to always run at its thermodynamic sweetspot.

You've got to run the numbers but there are various regimens that will probably still make financial and environmental sense.


IMO, PHEVs with low capacity high cycle (think lithium titinate) batteries make a lot of sense with highly efficient range extenders. I could see a 1 liter I4 with this injection/combustion technology, an 8kw/h high power LiTi battery, and a pair of wheel hub motors powering the rear wheels of a mid sized sedan. With no transmission tunnel and no rear differential/rear axle such a car could be very roomy and versatle. Costs shouldn't be too much higher either. The battery would cost about $8k but this would be partially offset by not needing a transmission, drive shaft, rear differential, or rear brakes. There would be some efficiency loss by having the regenerative braking come from the rear of the vehicle but it shouldn't be too big.

If someone could figure out how to make an engine that didn't need 100+lbs of cooling accessories that would be another big step forward.


In a different thread on this site, some want to end funding of research and development in this field. I hope this will not happen and that we will see results like this presented at DEER conferences for many years to come.

There is an optimum compression ratio in a diesel engine for maximum efficiency. At too high compression ratio, heat losses, friction, combustion efficiency, dissociation etc. will suffer. The optimum differs somewhat from engine to engine. If maximum cylinder pressure would not be a limit, the optimum is around 20:1. The best passenger car engine so far (VW Lupo 3L & Audi 3L) had a compression ratio of 19:1 and an efficiency of 45.1%. Contemporary “best” car engines have lower compression ratio (16-17:1), marginally lower efficiency but much higher power density. The desire to increase power density and downsize might favor a somewhat lower compression ratio to achieve best a-v-e-r-a-g-e efficiency in a driving cycle. It is likely that PPC (or PCCI, if you prefer) would have an optimum compression ratio in a similar range, implying that the level of 18:1 used by the authors is a very good choice. A compression ratio of 36:1 is far beyond the optimum.

Note that the level of 57% is an indicated efficiency. With a mechanical efficiency of 90% (might be somewhat higher at the optimum operating point) we would get 51%, i.e. still very good. Turbocompounding and a rankine bottoming cycle could increase this level up to ~60%. Low-temperature fuel cells have no improvement potential in this respect, since the “exhaust” is cold.

Perhaps better than gasoline would be to use a kerosene type of fuel, i.e. a fuel that has lower octane and cetane fuel than gasoline and diesel fuel respectively. This fuel could be produced at higher efficiency that gasoline and diesel fuel. Furthermore, the share of the crude oil barrel could be increased. Texaco has ideas like this some 25 years ago. On the negative side would be the need for a separate fuelling infrastructure.

If we compare to an electric car, we have to PAY less for this solution in a foreseeable future. As Heywood et al. at MIT have shown, the ICE hybrid is more efficient than and electric car with US mix of natural gas and coal power. PPC could further increase the advantage. Electric motors and fuel cells are ancient inventions. The otto engine is newer and the diesel engine is the newest. PPC might be considered even newer but I should then remind you that this was actually the starting point for Rudolf Diesel. However, he did not succeed with this PPC type of engine, so we ended up with the engine that we now consider as the conventional diesel engine instead.

I could see a 1 liter I4 with this injection/combustion technology
Fiat's 0.99 l Twinair is more than hefty enough for passenger hybrids and needs only 2 cylinders. This cuts heat losses and parts count.

This makes me curious about Transonic Combustion's supercritical injection system. It might lend itself to PPC and the supercritical fuel system allows recycling of exhaust heat to the combustion chamber through the fuel mix. Regenerative systems are a proven way to increase thermal efficiency.

fred schumacher

This technology would fit in well with what I call BBV, the Battery Buffered Vehicle.

Some 15 years ago, I started seeing vehicle morphology as the greatest impediment to a paradigm shift in isotropic transportation.

A big part of the problem was the need to size an engine for the needs of very infrequent, high power demanding events while operating the engine lightly loaded the majority of the time, resulting in lower efficiency.

In my mind, a better solution would be to operate a small engine continuously, in its most efficient power band, buffering output through a battery pack to meet continuous low-duty power demand with short-duration high power spikes.

Combine such a power source with hubmotors requiring no mechanical drivetrain, and the morphology of the vehicle can be changed to achieve highest usable interior space with the least exterior volume and mass.

The genset could be placed anywhere, since it would be small and light; the battery pack, smaller than would be required by a pure BEV, can be enclosed in a torsion box floor forming part of the load bearing structure of the vehicle and reducing center of gravity.

The result would be a vehicle offering more with less: higher efficiency at lower complexity and cost.


A range extender using this ICE would hardly use 3L/100km.
When using synthetic fuel made out of nuclear or renewable and CO2+H2O at 2$/L, it would still be much cheaper than a large battery. (even though 2$/L is extremely expensive)
If a car drives 300000 km before retiring, and you drive 10% electric, you would need 2700x3 = 8100L = 16200$ of fuel.
Try to buy a 1000-km-range battery for that price!

This ICE make zero-emission cars much more feasible and economical.

(1 litre of diesel is about 35 MJ. With a conversion efficiency of (renewable/nuclear) electricity-to-fuel of 50%, you need 70MJ/litre = 20 kWh)


Using dissociation/reforming will put more energy in the combustion chamber than supercritical injection but is difficult to realize practically (turbocompounding+rankine is easier). The highest potential for this type of "chemical compounding" would be for methanol fuel. However, you cannot use the heat twice, so you have to choose the best route. Supercritical injection might be of interest for PPC but if it is not needed, why not use conventional injection. By the way, I prefer a 3-cylinder engine over a 2-cylinder due to NVH constraints, although the cylinders are smaller in the former case. Nostalgic owners of some old Fiat cars might disagree…

To put things into perspective, I could mention that Johansson and co-workers have a goal to achieve 60% efficiency in their project. You need some king of waste heat recovery to reach this target.

Schumacher. A series hybrid is significantly less efficient than a parallel or combined hybrid, so down the drain goes the arguments for this option.

Nuclear power, no thanks!


OPEC should be quaking in their boots. Advanced combustion in the ICE with much more controlled combustion along with electrification will work to make the demand for fossil fuels to plummet. This is not news to the educated scientists and engineers but is astounding to those who have consumed the green lotus and constantly predict $5 - $10 gasoline in the future.

And at a time where OPEC greed has provided lots of other oil consumers outside of transportation users, to seek and have found substitutes.

It is starting to show in usage statistics. But there is a big spike downward in demand yet to come, as this research fully indicates.

The OPEC monopoly is aging, and losing power daily.


You forget that OPEC can put the brakes on substitution by cutting production, forcing prices up and re-directing money from investment into immediate needs.


No, they can't.

Just like our governements can't just double taxes to fix the budget deficit, OPEC can't just cut oil sales.

The OPEC countries are more addicted to petrodollars, than we are to oil. Even more, aside from decreasing demand, there will be increasing (synthetic) alternatives, so OPEC is not only losing its grip because the total demand will decrease, but even more because they will represent a decreasing fraction of the world fuel-production.


I am afraid that - within a couple of years - when Peak-Oil hit us really seriously, we will be on our knees in front of OPEC (or else, point our weapons at them…). In the meantime, we must do whatever we can to reduce fuel consumption.


Peter XX,

We both seek to improve the air quality and thsi research indicates that we can expect the proliferation of Diesel semi-diesels, and advanced combustion cycles. There will be more fine particles emitted into the air.

We had a discussion of this in a recent post.

I found this post about particulates and thought you might like to look at the results. It is most interesting and perhaps illuminating.


I suspect that long before OPEC forces anyone to their knees, negotiated prices and quotas will precede the rattling of swords. U.S. imports 53% (2007)of its oil from OPEC. We can expect to cut that in half over the next twenty years or less. And we may choose to import more from non-OPEC nations (primarily Canada.)

In any case the technical issues will take back seat to economics and politics. There is little political will to continue importing oil from nations perceived to be hostile. Since we have little domestically produced oil any longer - an alternative is necessary. The best political, economical and technical alternative? Electric energy. Made at home. With domestic resources.

As we transition to BEV/PHEVs it would be interesting to factor the number of new jobs electrification creates inverse to the decline in oil imports.

It's rather simple. We do not have oil. We DO have the ability to make lots of electricity. Pleasing to any who care about air quality.


If this invention is confirmed it will certainly not kill the electric car but would probably delay its mass adoption as long as the range of electric car is so limited and the price of battery so unaffordable. That's where it is difficult to predict the future in matter of technology, it is often easier to improve an existing technology than to introduce a new one. Anyway 57% efficiency is absolutely incredible for an ICE, couple this with an hydraulic braking recovery, drop the Cd to 0.2 (quite possible and already demonstrated) and you have a mileage close to 100MG car even the size of a Sedan.

OPEC can put the brakes on substitution by cutting production
No, they can't.
They did. Saying they can't makes you look mighty foolish.

Yes they can, they did it in 1986 and by a large amount in order to reverse the trend in the collapsing price, problem is that it was too late, after 3 oil shock of the 70s the world had learned how to be less reliant on oil, so it didn't produce the expected effect, plus the OPEC members bump their reserves to increase their allowed production quotas. That is why Saoudia is extremely careful not letting the price of oil increase too fast, they know that it sooner or later backfire and the result is very painful for them when their customer reduce their dependence to oil...believe me they don't like the electric car

Roger Pham

May be there is something that I am missing here. Maximum theoretical efficiency for an Otto-cycle engine at a CR of 10 is around 56%, if memory serves accurately. This theoretical efficiency ignores heat transfer loss and friction loss, which would be impossible to achieve in a real engine. It is not possible to run a pre-mixed charge engine at a CR of 18 on "regular US gasoline" due to detonation. BTW, how do they obtain "regular US gasoline" all the way in Sweden, instead of using regular Swedish gasoline?

An Atkinson-cycle engine like the Toyota 1NZ-FXE with a CR of 13 gets around 37% brake thermal efficiency in real life, while research Atkinson-cycle engines can deliver up to 40% efficiency MAXimum, in the laboratory.

A Diesel cycle engine at CR of 18 has a theoretical efficiency of ~65%, but of course, for obvious reasons, real-life automotive turbodiesels get about 45% efficiency max. A theoretical engine does not really care how the fuel is injected or ignited. Otto cycle is calculated as constant-volume heat addition, and Diesel cycle is calculated as constant-pressure heat addition. Real-life engines of gasoline and diesel varieties fall between those two ideal processes of heat addition.


the 57% also seems very optimistic too me, maybe they correct from heat losses.

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