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

Interesting

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

"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.

@Goracle,

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.

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.

http://www.greencarcongress.com/2010/09/deer-20100927.html#more

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.

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.

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!

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.

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.

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.

OPEC can put the brakes on substitution by cutting production

No, they can't.

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.