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BMW Developing Steam Assist Drive Based on Waste Heat Recovery

BMW’s Turbosteamer. Click to enlarge.

BMW Group Research and Engineering is developing a steam-powered auxiliary drive—called the Turbosteamer—that uses the waste heat present in the exhaust gases and cooling system from a conventional gasoline engine as its source of power.

In tests with a 1.8-liter, four-cylinder engine, the new auxiliary power unit reduced fuel consumption by up to 15% while generating nearly 14 additional horsepower and 20 additional Nm of torque.

The Turbosteamer is based on the same principle as the steam engine: heated fluid forms steam in two circuits which is used to power the engine.

The primary energy supplier is the high-temperature circuit which uses exhaust heat from the internal combustion engine as an energy source via heat exchangers. More than 80% of the heat energy contained in the exhaust gases is recycled using this technology, according to BMW.

The steam is then conducted directly into an expansion unit linked to the crankshaft of the internal combustion engine. Most of the remaining residual heat is absorbed by the cooling circuit of the engine, which acts as the second energy supply for the Turbosteamer.

The Turbosteamer reinforces our confidence that the internal combustion engine is undoubtedly a technology fit for the future.

—Professor Burkhard Göschel, BMW Board of Management

BMW designed the components of this drive system to fit in existing model series. Engineers carried out tests on a number of sample packages to ensure that a car such as the BMW 3 Series provides adequate space. Their conclusion is that the engine compartment of a four-cylinder model offers sufficient space to accommodate the auxiliary units.

Ongoing development of the concept is focusing initially on making the components simpler and smaller. The long-term development goal is to have a system capable of volume production within ten years.



Thank you Professor, but sustainable mobility is also a political choice.


Awsome idea. No batteries required.


Interesting, but complex--similar in concept to high-efficiency combined cycle power plants. How does this mesh with BMW's avowed intention to include idle-stop and regen braking on all their cars? Sure seems like a lot of complexity under the hood, with attendant higher costs and expensive maintenance.

tom deplume

14 hp is plenty for idle stop and low speed use. Many steam cars were heavier than this and performed well with only 10 hp engines. The question I have is how much energy can this boiler store?

Robert Schwartz

"Sure seems like a lot of complexity under the hood, with attendant higher costs and expensive maintenance."

Their current products are not priced for the mass market.


And the people who buy them won't be enticed by 15% less fuel consumption.

Roger Arnold

Some complex tradeoffs here. If there's a significant amount of high pressure steam storage, then the system offers some of the same performance features that make hybrids attractive. I.e., high torque at low speed, enabling a smaller engine, and idle stop capability. Good fuel mileage, but no regenerative braking.

Where something like this could make sense is in a plug-in serial hybrid. The engine would be undersized, delivering somewhat less than the average power needed for freeway driving. It would be run full on to extend the range of what would be mostly a battery EV.


If the engine didn't have a catalytic converter, the steam generator could be mounted very close to the engine where it could capture even more of the engine's heat. The cat could be mounted after the steam generator but would be less effective due to the heat loss. Unlike a hybrid, this system is more effective at constant speed, high load such as driving on the freeway when the engine generates the most heat. Very reminescent of the compound turbo.

tom deplume

Catalytic converters add energy to the exhaust stream by burning fuel that wasn't burned inside the cylinders. It may be advantageous to use an inherently dirtier but smaller engine like a two-stroke or wankel. The small engine would be essentially an apu in which its exhaust is burned inside a larger boiler and using the steam for vehicle propulsion. Something similar was tried in the 1920s but never went into production.


"Catalytic converters add energy to the exhaust stream by burning fuel that wasn't burned inside the cylinders."
I don't think so. Check out the temperature drop from the manifold to after the cat.


Very reminescent of the compound turbo.

Exactly. Turbocompounding sure sounds simpler and lighter weight than adding a full-featured steam engine.

IIRC Scania is using it in some of their newest truck engines.


Turbocompounding can't recover energy beyond expansion of gases to atmospheric pressure; a steam system can.

What amazes me is that a system like this has not already gone into diesel ships and heavy long-haul trucks.  They seem ideal.


What they should do, and maybe have, is study all possible bottoming cycles, including stirling engines ( my one note theme, endlessly repeated) Stirlings are compact and highly reliable these days, and recover available energy better than steam cycles. You can arrange a multi piston stirling to receive heat at several temperatures, analogous to a multiple expansion steam engine, all blowing the stirling working gas over one turbine, which could be driving an alternator, or be geared to the engine.


I like to believe that I pull out unobvious things from what I learn, yet I never even thought about a Stirling engine which receives heat at several temperatures.

And I become a little more enlightened.


This system might not have gone into diesel ships, because the exhaust temperatures are already significantly lower. Diesel engines have a much higher compression ratio and a turbocharger. Both, high compression ratios and turbochargers lead to lower exhaust temperatures.
The potential gains on a gasoline engine should be significantly higher. Although, I wonder how effective this system is at mainly partial throttle operation.


What's not to like? Free power with better fuel economy? Sounds good to me. Unfortunately, the extra cost to implement this sort of system is weighed against the cost of fuel. These systems were considered in the U.S. during the '70's oil crisis but cost shot them down - along with the prospect of a toxic, high pressure, flammable working fluid under the hood. We have better fluids now, better electronic controls, and a greater need to reduce overall vehicle heat rejection. Does anyone know what fluid BMW is using here? Note that they're doing all of their engine cooling with this system.


What's not to like? Free power with better fuel economy? "

Er, its not free if it adds systems complexity and weight to the whole engine ... but it may be worth it.

"similar in concept to high-efficiency combined cycle power plants."

Exactly so. and the 'turbocompounding' concepts. ICEs today top out
at 40% thermal efficiency, but combined cycle power plants push it over 50%. This apparently may do the same thing.

"What amazes me is that a system like this has not already gone into diesel ships and heavy long-haul trucks."
Good point.

MZ doctor

Been there, done that -

Check out the website of MAN B&W/marine propusion/two stroke engines.
There you will find a pdf document describing their "Thermo Efficiency System" which can be added to their "cathedral" engines. The base efficiency of these reciprocating ICEs already exceeds 50%.

When equipped with a generator driven by an exhaust turbine that utilizes exhaust gas power not required for the turbochargers, as well as by a steam turbine utilizing the remaining heat, the overall efficiency is about 55%. The electrical power is fed to a motor on the propeller drive shaft. The downside is an investment payback period of around 5 years.

So there you have it: the ultimate diesel/steam/electric triple hybrid.


Since it also uses the car radiator for a heat exchanger, would it not mean a bigger radiator, or a second radiator for the special coolant? Or am I reading the diagram wrong?

The positive can be that it complements regenerative breaking, because a car idling at traffic lights will heat up considerably more, thereby creating more heat that can later be used as a boost to get it going in the form of electric energy.

The system does not appear to be that large. I'd like if it was available as a kit for all cars, seeying as how custom exhausts once thought to be for racing guys is commonplace now. The electricity generated does not have to be linked up to some fancy electric drive system. It may just accumulate to be used to complement incar electronics. At the very least a complement to the alternator when the car is idle.

Also, how do you think this system compares to the fuel vapouriser thats supposed to use the exhaust to heat incoming fuel so when it enters the intake its close to boiling point necessitating better mixture hence better burn? I know its not the same thing, but in essence it uses the exhaust energy so I thought to give it a mention.

Paul J Ordway

Please add me to your blog.


when will this car be produced or be available for the public to purchase?

how much will one of these cars cost?

will they be low maintenance vehicles as far as car parts go?

will they be considered a sports car or a town car?


Overengenerring. Heard the phrase? People need a CHEAP replacement for the combustion engine not something designed for the sole purpose of keeping them attached to the oil pumps!


I've been telling people this idea since gas hit $1.00 a gallon. Only difference is this "Turbosteamer" is much more complex than my idea. Mine was a simple steam driven design with the water already in the block being super-heated by the exhaust via a simple heat exchanger to drive the turbo. As for the high emission problems, incorporate the catalyst in the exchanger. As previously pointed out, a low design / production cost idea that can be retrofitted to ANY existing vehicle is the golden egg.


German's do tend to over engineer stuff (and that is why I keep buying their cars). That said, once you get an electric motor to handle the traction, the ICE can be reduced in size and cylinders to a mere constant RPM charging module. Add a Sterling or Steam heat recovery system and you have two devices providing power on board. e.g. ICE for the high voltage traction system and the Sterling for the low voltage auxillary (airconditioning etc.). Once the industry and the consumers adjust to this, perhaps the cost of the unit can be reduced.

Stephen S. Mueller

During the early years of automotive developement when both gas and steam vehicles were produced, a combination of both was tried. The car was called the "Compound". It features a three cylinder engine. The two outer cylinders ran on gas and both alternately exhausted into the center cylinder which functioned as a steam engine. The outer cylinders had four inch pistons and the center cylinder had an eight inch piston. One of the advantages of this configuration included low noise output as the steam cylinder absorbed a lot of the noise. As far as efficiency and fuel milage I have no idea. If a catalitic converter was added between the gas and steam cylinders along with water injection to convert the extra heat to more steam pressure before entering the steam cylinder, this type of engine might prove to be efficient yet somewhat simple. What do you think, and does anyone have further and more detailed information about the Compound automobile?

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