SAFT providing Li-ion cells for KERS systems for 5 of 12 competing F1 teams
Nanocrystal tandem catalysis a promising approach towards designing high-performance, multifunctional nanostructured catalysts; energy applications

Toyota targeting thermal efficiency of more than 45% for next-generation gasoline engines for hybrids

Among the R&D projects Toyota Motor is exploring to further lower fuel consumption and emissions are two concepts on a pathway to deliver gasoline engines featuring more than 45% thermal efficiency for application in its future hybrid vehicles, according to Koichi Nakata of Toyota in his presentation today at SAE 2011 High Efficiency IC Engines Symposium in Detroit.

The engine used in the first- and second-generation Prius (the 1.5L 1NZ-FXE) had a thermal efficiency of about 37%; the thermal efficiency of the new 1.8L unit in the third-generation Prius (2ZR-FXE) has a thermal efficiency of about 38%. Toyota is targeting a thermal efficiency of more than 40% with what Nakata called its Future Concept 1, followed by thermal efficiency of more than 45% in Future Concept 2 (which is based on concept 1).

In the 2ZR engine (third-generation Prius), some of the main technologies Toyota applied are the Atkinson cycle with variable valve timing to control intake valve timing, cooled EGR, and lowered friction. (In the 1NZ engine, Toyota reduced friction 21.1% compared to an engine for a comparable conventional vehicle; the 2ZR engine in the newest Prius drops that another 26.8%, in large part by the removal of parasitic loads via the hybrid system (e.g., no alternator).

Concept 1 is a cooled EGR stoichiometric spark-ignited direct-injection concept, featuring a long stroke design (stroke/bore=1.5) and cooled EGR with an EGR ratio of more than 30%. The long-stroke design (lengthening the stroke while maintaining displacement), reduces heat loss and also increases piston speed, creating more turbulence. A high tumble ratio intake port (TTR=3.0) and a high-energy ignition system (100 mJ) also contribute to improved combustion. Toyota is continuing to reduce friction.

Concept 2 is a turbocharged lean burn concept, built on the base of concept 1. It also uses the long stroke design, with a high tumble ratio and a higher-energy ignition system (150 mJ).

The high tumble ratio intake port extends the lean limit from 19 to 23, Nakata said. In addition, the lean limit is also increased by using a spherical face on the piston. Furthermore, the high discharge current in the ignition system also gives a higher lean limit.

Nakata said that the engine team has currently delivered a 42.4% thermal efficiency in concept 1 and 43.7% thermal efficiency in concept 2.

Work is ongoing, focused on increasing the expansion ration and decreasing pumping loses. Toyota is also considering a variable super high expansion ratio cycle for further improvements. Nakata suggested that such an engine applied in a hybrid would result in total lifecycle greenhouse gas emissions comparable to that of an electric vehicle.



So, 45%/37%=1.21! Would that mean a Prius would go from 51 Mpg highway to 62 Mpg?


That sounds about right, the 60 mpg car may be possible soon. The PNGV cars all got 70 mpg as four seat sedans in 1999 with a diesel hybrid configuration, so this sounds reasonable.

Roger Pham

Good work, Toyota!!!

However, applying the above principles to a direct-injection Hydrogen fueled engine, thermal efficiencies at 45-50% can be realized without needing cooled EGR nor necessarily high energy ignition system nor turbocharging. H2 has much higher lean-burn limit than gasoline without requiring turbocharging, and requires much less energy to ignite. Furthermore, H2 combusts very rapidly, leading to isochoric combustion for maximum power and efficiency harnessed by the piston. When high power is momentarily needed on rare occasions, the H2 can be combusted stoichiometrically, resulting in high power density.

If the H2 is produced from renewable sources such as solar and wind generators, then the life-cycle GHG produced would be zero.



From well-to-wheels, don't you have to count the storage and transportation losses, not to mention the latent energy content of the as-yet-to-be-created H2 infrastructure? H2 could easily give back that 5% and more when those values are counted.

Roger Pham

One day, with solar PV's on every roof top and a wind turbine on every acre of farm land, H2 can be produced and stored locally in the same community where it will be consumed, thereby no transportation losses. For agricultural waste biomass, the raw material can be transported in dried form to be gasified to H2 near the point of consumption.

The building and maintenance of H2 infrastructure will amount to millions of jobs created locally. The H2 will be produced locally, resulting in more local that can't be exported or nor outsourced...! The elimination of oil importation will keep hundreds of billions of USD here at home to invigorate the US economy!!! A win win win combination, as far as I can see it!!!


You could use the new MIT method with built in solar cells and get hydrogen at the station from water and sun. The whole quarter acre gas station property would have to be covered by awning, but you could fuel a few cars.


    thermal efficiency of more than 45%

That's the way to go! :-)

Good work, keep raising the bar.


BTW, range-extenders as in a GM VOLT v2.0 should do the same.

It should be easier in a Volt-like than in a Prius-like setup, as with bigger batteries and electrical motors Volt relies less on ICE for the dynamics.

Couple it to Lund's PPC findings and deliver a flex fuel with a thermal efficiency north of 50% !

(RangeExtender: 2cyl-Turbo-DI-EGR-FlexFuel-Miller/PPC-LowFriction-60kW @ > 50%TE !)


Gee, if i had solar panels and wind generators on my roof i'd just be turning that electricity into..... electricity! forget the intermediate H2 step.

Battery tech continues to improve and energy density is going up year by year. I'll place my bets on EV...


I vote for neptronix



"One day, with solar PV's on every roof top and a wind turbine on every acre of farm land"

Long before that could happen there will be a battery tech that could store 100kWh in a shoebox size container weighing 20kg. Why bother with the H2?

Roger Pham


H2 technology is available here and now. The 100kWh battery the size of a shoe box is still science fiction that may or may not materialize. Oil is running out and becoming more and more expensive...We also need more jobs, good-paying, local jobs that can't be exported overseas. We have no time to wait nor to waste!


Roger Pham,

Electrics and Biofuels are already more developed and more economical than hydrogen, we should not waste time and money on hydrogen.



H2 technology is pie in the sky.

45% efficiency for a gasoline engine is quite an outstanding achievement indeed, and will probably help us to be patient in our wait for the perfect electric car...


Two comments:

1. 37% thermal efficiency sounds very high. At what kind of load and what kind of on/off duty cycle is this achieved?

2. The hydrogen economy: Please read


(I hit post too fast) The hydrogen economy is less efficient than the electron economy, as is shown in the above paper. All the losses related to producing and compressing hydrogen as accounted for in the paper.


Toyota gets it.

The next generation Prius with the concept 1 engine, a lighter and more powerful li-ion battery, and likely a lighter chassis will likely get >60mpg highway and >70mpg city.

Now Toyota just needs to switch to a Torlan engine block, pistons, and cylinder head to drop the weight and the price of the Prius!



    37% thermal efficiency sounds very high

A lot of people make a confusion about it when boundaries are not well defined. Only the ICE or the way it is used in a "standard car". An ICE in a traffic jam provides no motion...

This "thermal efficiency" of the ICE is at steady load in the best BSFC region.

According to many presentations in the DEER conferences sponsored by DOE (previously only about diesel engines, but covering other fuel nowadays) it's not high, but typical of best cases today.

There is a link to a thread where we discussed it before, and I posted some links to related material.

The idea behind the Toyota Prius HEV is using the small scale (and cost) electrification to allow the ICE to be used most of the time only at it's best BSFC regions, and only when needed.

This makes the energy conversion ratio of the ICE approach it's best "thermal efficiency" in real world use, both when driving the wheels and when recharging batteries.

As GreenPlease said: Toyota gets it!

There is a continuum in the design space where eAssist-like mild electrification, Prius-like [P]HEV, Volt-like ER-EV, will give increasing benefits avoiding the use of oil.

This Toyota solution raises efficiency, and IS great!

In a next step, pluggin-in with bigger batteries, while costing more, allow for energy source substitution/displacement.


greenhouse gas emissions comparable to that of an electric vehicle.

Unless you run your EV from a renewable source of course. But Toyota is falling behind on EV's so their PR department starts bending perception.


Roger Pham

H2 can be produced and stored locally in the same community where it will be consumed, thereby no transportation losses

Human population shows vast concentrations in small areas, called 'cities'. The H2 will have to be transported from the rural areas where it produced to the cities where it is consumed. Just like food.


You can find gasoline engines with ~36-37% peak efficiency today. Current Prius engine is somewhat better. Diesel engines in cars can reach ~43%. The question is how much improvement potential a diesel engine would have in the timeframe of Toyota´s Concept 2. Researchers (refer to e.g. the DEER conference) talk about 50% and higher for heavy-duty engines but car engines would most likely be a few per cent behind. In my assessment, the relative difference between diesel and gasoline will decrease somewhat during the next 5-10 years. The problem is that we cannot choose, we have to develop both in parallel. A certain ratio of gasoline to diesel from the barrel of crude oil gives optimum efficiency in the refinery. Alternative fuels, such as e.g. H2, can only play a minor role on this time horizon. Peak oil will hit us before we have any alternative fuel in any large quantity.


Lastly I would like to add that I am a very content Prius driver since 2005. But my next car (hopefully in 2013) *will* be an EV. If Toyota has no EV's by then, bad luck for them.

ICE's are soooo 20th century. Just not sexy enough for me, even at 45% thermal efficiency.


"Work is ongoing, focused on increasing the expansion ratio"

At last! 30:1 expansion ratio is where we need to be.


High expansion ratio is good for efficiency but it leaves less energy in the exhaust for the turbine, so boost pressure will decrease (and pressure ratio over the engine will deteriorate). It is difficult to use energy twice… However, it is surprising that Toyota has not yet tried with turbocharging to downsize the engine. Turbocharging (and supercharging) is an essential part of the Miller system that utilize the Atkinson cycle (as the Prius engine does). The loss in volumetric efficiency is compensated for by increasing manifold pressure.


I have an idea for increasing the thermal efficiency that I want to run pass anybody who knows more than I do about this. My idea is to eliminate the loss of energy through the cooling system. I figure that if the car is a PHEV its engine will spend a lot of time cycling on and off. If it spends enough time off you not only wont have to cool it you'd likely need to insulate it so that it's still warm when you restart it.

Does this sound right?

The comments to this entry are closed.