With so much attention focused on next-next-gen, alt-energy auto technology, we enjoy highlighting the incremental changes that are making good old internal combustion engines more efficient. The latest evolution to show up on our radar screen is BMW’s development of a host of measures [via Green Car Congress] which it hopes will someday reduce the inefficiencies of cold starts. Perhaps the easiest way of reducing low-temperature, high-friction starts is to encase the engine to slow down the engine cooling process (as well as insulating components that might otherwise need to be cooled). In fact, BMW has shown that with encapsulation, a 176 degree operating-temperature engine can keep its temperature as high as 104 degrees after 12 hours. But good luck trying to change your oil when your engine is surrounded by thermal materials.
BMW is also looking at exhaust gas heat exhangers to provide quicker warm-ups and even interior heating. But heat is free in an ICE, you say? High-efficiency diesels are actually so efficient, that many manufacturers have had to include electrical heating elements to provide sufficient interior heat. As gas engines become more diesel-like and thermally efficient (possibly with the advent of HCCI), they too might need to look at using exhaust heat for cabin heating. In any case, this technology won’t improve test-cycle efficiency because the engine would already be warmed up, but BMW says modern diesels should see noticeable improvements in everyday driving.
Perhaps the most radical gizmo being developed by BMW is the thermoelectric generator, which the Bavarians are showcasing as a component in exhaust gas recirculation systems. By integrating a thermoelectric generator just downstream from the exhaust manifold, a thermoelectric generator can develop as much as 250 watts of energy (equal to about a 2 percent efficiency improvement) without interfering with exhaust gas recirculation cooling or pressure. The only shortcoming at this point is size, which (as you can see from the picture above) makes integration a bit awkward. BMW hopes to eventually use its thermoelectric generator on exhaust systems, where higher flow holds the potential for greater energy generation. In that future application, a thermoelectric generator could also be used to more rapidly heat up a catalytic converter, reducing cold-start emissions.
BMW’s recent technology may not be earth-shattering, nor immediately production-ready, but it shows that there’s more to the future of the automobile than battery chemistry or fuel cells.
As said in my best Geddy Lee falsetto: “Take off to the Great White North.”
The thermoelectric generator sounds interesting. Something like that could bump up hybrid efficiency by charging the batteries whenever the gas engine kicks in. I’ve long thought that throwing away that heat seemed wasteful.
Too bad BMW doesn’t achieve some breakthroughs in not breaking down or better part-cost competition. Or maybe some new, “anti-money-pit” technology.
BMW has some very cutting edge techno ideas. I always felt to lower the friction on an engine when it is started cold simply installing an accumulator that pressurizes the oil system before the car starts would help greatly. The same as many dry sump race cars have had for years.Combining this with a low pour point synthetic oil would do the trick without all the high tech BS.
Thanks for the good informative article.
Denis
BMW were working on the Turbosteamer in 2005 which used waste heat from the IC engine to drive a steam engine. Honda also tried the same thing. Apparently the efficiency gains didn’t justify the extra weight and complexity.
And Volkswagen were developing an external thermal storage in an insulated canister of molten salt, which wouldn’t interfere with engine access.
Interesting. Thanks.
Wouldn’t a $40 engine block heater solve the cold start problem?
Silly you, SherbornSean: This is German engineering at its best! The simplest answer is clearly unacceptable!
Wouldn’t a $40 engine block heater solve the cold start problem?
It would, except that an external power supply sort of negates the whole recapturing-of-lost-energy thing.
I recall an old Popsci article by Smokey Yunick, in which he postulated (in his usual colourful way) that advances in ICE thermal efficiency are the key to future powertrain design. He spoke of run-of-the mill GM “iron duke” four-cylinder mills being capable of wild amounts of horsepower with incredibly frugal consumption, if you could simply recapture more of the wasted heat energy. Sounds like the Germans are putting some of that theory to work.
Seeing as how hybrid and electic cars like the Volt, the Prius, and the Telsa need to figure out how to generate heat or cooling while in electric mode, it should stand to reason that in future cars the HVAC system will be 100% electric and power plant agnostic.
Removing the need for heat production from the motor frees up the designers to concentrate on making it as energy efficient as possible. Hell, perhaps future electric motors might be housed in something to keep them close to absolute zero where electrical resistance drops to zero. So instead of heat, the motor will be mind numbingly cold.
A few years back I read about a gas-steam hybrid from Mercedes, I think. They used exhaust heat from the ICE to boil water and turn a turbine to give a small bump in horsepower. It sounded like a pretty easy and inexpensive way to get a little more efficiency. I haven’t heard anything about it since, though. I wonder what happened with it.
Jonathan:
one of the problems would be that it takes a while to heat up enough steam. Say you are cruising, then you don’t produce much heat, hence the boiler is not full of steam. then you want to race another car and the IC kicks in and produces heat… that would mean some additional lag time till your steam generator produces enough steam. Once it does, you typically are done accelerating already.
On the other hand, it might be possible to keep the steam generator hot and under pressure just from cruising when you don’t use the steam turbine.
but I think in the end this technology might have been too heavy, too expensive, had too much maintenance and probably not much merit. If you don’t get steam into super critical condition it is not very efficient.. but having super critical steam might be a safety hazard too. If they used a turbine, they probably didn’t have a real way to funnel that energy into the transmission. Possibly one could run a generator and support the hybrid E-motor. but we talk about 3 motors (ICE, E-motor, steam turbine) and that doesn’t sound economical and lightweight. you know how often a Mercedes has to go in for expensive repairs with one motor? Do you want to go in with 3 motors? :-)
Since I live in Hawaii I wouldn’t know… but are cold starts that much of a bad thing, efficiency-wise?
Radial aircraft engines used power recovery turbines in the 1940s. An exhaust driven turbine coupled to driveline. They ran at steady speeds at high altitudes though and it was not cheap. If I remember it added like 10% free hp.
Car companies are looking for fixes that cost a few dollars per fix per car at the plant.
“He spoke of run-of-the mill GM “iron duke” four-cylinder mills being capable of wild amounts of horsepower with incredibly frugal consumption, if you could simply recapture more of the wasted heat energy”
We call such devices “turbochargers”
“Car companies are looking for fixes that cost a few dollars per fix per car at the plant.” YMMV. I can think of several fixes for fuel consumption/emissions that cost of the order of a hundred dollars per car (VCT, DI, better cats). These days if it reduces total cost of ownership (ie it pays for itself) then you can even hit marketing for some of the development cost.
Smokeys experimented with (adiabatic) engines, one being a two cyl. in a VW Rabbit.
Well, one engine, the Wright 3350 Turbo Compound radial had 3 symmetrical turbos feeding the output shaft through a variable speed drive. Mostly in the 1950s, though, in Constellations and DC7 airliners. Other attempts failed, P&W in the USA and Napier in Britain.
Since at least a third of the available energy goes out the exhaust, and another block to the radiator, it does seem to be a good idea to try to recover some of the energy. Hard to do in as small a space as a car, though.
My thought is to use a real compressor turbo to pump up a tank of air to 30 or more psi, and keep it there no matter the revs, so that the engine thinks it’s living on a new planet with 45 psi atmospheric pressure. No turbo lag, no supercharger parasitic losses, and the ability to really run lean burn direct injection around the spark plug, when required. That and no throttle plate, as per Fiat Multiair or BMW or Infiniti systems. Then the displacement can be reduced by two thirds, and friction and cooling requirements decline as well. Better economy, yet snappy response.
I havent heard of any automaker adopting turbo compound, or power recovery turbines. Has this idea been lost to history? 20 percent of the waste exhaust heat was recovered in the engines powering the DC-7 and Constellation airliners of the 1950s, allowing for intercontinental range.
Converting exhaust heat energy into electricity is sure an interesting idea, especially if the vehicle is some sort of hybrid with battery packs to store the recaptured energy in. Alternatively, the exhaust heat derived electricity could at least provide the power for the cars electronics instead of using mechanical energy from the crankshaft via the alternator. BTW, from the Green Car Congress article it sounds like BMW is using a Seebeck effect device to directly convert thermal energy into electrical energy. http://en.wikipedia.org/wiki/Thermoelectric_effect
The cold start issue BMW is going after is a serious energy waster and goes well beyond lubrication issues. BMW is doing very interesting work in this area.
WMBA, didn’t Audi have some sort of compressed air storage to spool the turbos on the Pikes Peak cars? sounds similar to what you are saying.
High-efficiency diesels are actually so efficient, that many manufacturers have had to include electrical heating elements to provide sufficient interior heat.
Is that right? Thanks to Sadi Carnot and his pesky second law of thermodynamics, even the best diesel engines get just over 50% thermal efficiency. That’s not enough waste heat?
Exhaust heat energy can be turned into electricity. And there is usually plenty of waste heat to work with. The trouble is getting enough electricity to matter.
A heat-to-electricity converter has an efficiency well under 10%. People have been trying to improve that for years, with little luck. No reason to stop trying. But I’m not holding my breath.
Since I live in Hawaii I wouldn’t know… but are cold starts that much of a bad thing, efficiency-wise?
Engine efficiency is proportional to operating temperature. Someone once complained to Tom Magliozzi (Click, of cartalk) that his gas mileage had tanked, like to half of what it had been. It turned out the guy had moved, and was living a mile and a half from his office. That was the “problem.”
Johnny Ro & Nikita beat me to the punch. Older radial aircraft engines often had the turbo geared to the crankshaft. For quick throttle response, it worked like a supercharger- instant. For high power demand, it worked like a turbo- efficient intake air compression. For steady state cruising, it recovered exhaust waste heat and added that power directly to the crankshaft. All this was inherent in the design- it’s just a normal turbo with a bevel gear connected to the teeth on the flywheel, more or less. It just does whatever is needed, with no control mechanism necessary- it’s inherent in the design.
Here’s another way to think about it. Superchargers extract power to the engine to compress air. Turbos extract waste power from the exhaust to compress air, which is more efficient but less responsive. You only need to compress intake air when you need bursts of power. So, why not take that waste heat the turbo is extracting and add that to the crankshaft power ALL THE TIME. Then, use a supercharger when you need extra power. Normally, the power generated by the turbo will just add to your output power with no extra fuel burned. When you need an extra boost, the same amount of power (more or less) the turbine is adding to your crankshaft can be used to power the supercharger, via the crankshaft if necessary) Pretty simple and ingenious concept. Turbo compound.
Alternatively, you could gear a turbo to an electric motor/generator. When you need high power, it’s a normal turbo. For quick response, kick on the motor to spool the turbo quickly (you can then run a bigger, more efficient turbo without worrying about lag). For steady state cruising, kick on the generator and scavange exhaust energy to drive the electric motor in your hybrid system.
Professor Andrew Frank at the University of California at Davis has a patent on using exhaust heat in a car to get better efficiency or to generate electricity. http://www.pat2pdf.org/patents/pat6931850.pdf
I’ve spoken with him about his patent. He concedes that at most you might get about 10% more efficiency. Right now, and most likely for the future, you get perhaps 3% better efficiency, if that. Not much good for what you need to do to get it.
“a thermoelectric generator can develop as much as 250 watts of energy”
The watt is a unit of power or energy/time (joules/second).
We call such devices “turbochargers”
Wrong. Turbochargers do not recover heat energy; they simply transfer kinetic energy from the exhaust manifold to the intake manifold. The residual heat produced by combustion is still wasted.
The boiler device described by Jonathon above sounds more like it.
Ok, so I see a couple of problems with some of these ideas. Not that I’m an engineer or anything, or even that smart. I’m just an enthusiast.
Anyway, WMBA, the problem with your idea is the sheer volume of gas running through an engine. Even a 1200cc engine running at 2000rpm uses 20l of air per second (yes, I’m assuming 100% volumetric efficiency, so it would be less). Just imagine the tank sizing needed there…. I just don’t think it’d be practical, not to mention trying to run an engine (reliably) all day every day at 30+ psi. (I’d be happy to be proven otherwise though).
On the idea of powering other auxillary devices by an exhaust turbine, with the exhaust pressurised and the inlet at atmosphere you’d have problems with backpressure in the cylinder, unless you retarded the valve timing significantly. Not a problem for low revving scavenging, but you’d lose efficiency at high RPM, exactly where you stand to gain the most from the turbine.
Like I said though, I’d love to hear why I’m wrong.
Don1967: gas turbines are heat engines- not windmills. Otherwise, jet engines would be perpetual motion machines: The compressor provides kinetic energy to the turbine, and the turbine uses that energy to turn the compressor. That won’t last long. The real energy added to the system is the heat. When the exhaust valve opens that hot gas would come rushing out of the cylinder even if the cylinder wasn’t pushing it out, just as they do on a two-stroke. That energy comes from the expansion of hot gas, and heat energy can be extracted from this expansion.
250 watts…. about 1/3 of a horsepower, on a vehicle with hundreds, for how much?
a thermoelectric generator can develop as much as 250 watts of energy (equal to about a 2 percent efficiency improvement)
250 watts is about a third of a horsepower. That’s not much. But even a vehicle with hundreds of horsepower uses less than 20 horsepower about 99% of the time. 250 extra watts may well give a 2% to 3% efficiency improvement in normal driving.
So I have to disagree with cmcmail a bit.
I drive a hybrid with several electric motors (RX400H), the display shows the current KW output needed to move the car, unless it is downhill or very slow and flat 30KW is fairly common, 250 Watts or 0.25 KW represents less than 1%. The saving from 160+ HP(120 KW’s) of electric motors is about 30% over gas only, adding or subtracting 250 Watts is nothing.
”
We call such devices “turbochargers”
Wrong. Turbochargers do not recover heat energy; they simply transfer kinetic energy from the exhaust manifold to the intake manifold.”
Wrong. wrongity wrong. The exhaust temperature after the turbo is much less than before it, because heat energy has been turned into work.
In a normal IC installation that work is used to compress the intake gas, but it could be geared to the crank, or an alternator.
Whoops. It was a BMW prototype, not a Mercedes, that I was thinking of. Here’s a relevant link.
cmcmail,
That’s interesting. 30 kW sounds too high to me. But if that’s right, you are right that 250 W is not going to matter.
Greg & carve,
Thank you for clarifying what was a “common misconception” on my part… what clued me in was the comment about two-stroke expansion chambers. I found this longer explanation, which pulls both of your points together: http://www.turboclub.com/turbotech/TurboFun2.htm
That said, the total percentage of heat energy recaptured by a turbocharger must be relatively small, and partially offset by the back pressure and frictional heat it generates. Is anyone prepared to argue that a 200-horsepower turbo-four puts out significantly less heat than a 200-horsepower normally aspirated V6?
Thanks for the reply, Don.
If the turbo extracted power from the exhaust and added it to the crankshaft, then yes: they’d put less heat out the exhaust for a given power output. However, turbochargers are almost exclusivly used to compress intake air, which increases power instead of efficiency. The same heat in a smaller engine means higher temperature, which is then cooled by expanding through the turbo. Heat & even temperature output at the tailpipe of a 200 hp turbo 4 is therefore likely similar to a 200 hp V6 when both engines are making their rated 200 hp. The advantage of the turbo engine is that it’s smaller & lighter, and it has reduced pumping losses while cruising. The advantage of the normally aspirated engine is that it has quicker, more predictible throttle response and is simpler.
If the turbo was geared to provide power to the crankshaft directly rather than compressing intake air, exhaust temp would indeed be cooler. The effect of this added expansion would be similar in principal to an atkinson cycle engine, which expands the charge to a greater volume than the amount drawn in and compressed.
The efficiency of heat engines is largely proportional to the temperature difference between the hot side (combustion fire) and cold side (ambient air). As the air in the engine is expanded, it cools off. Power output falls as the hot air continues to expand, and you need a much larger volume (bigger engine) to extract the leftover marginal heat. You’ll often refer to this as “quality” of thermal energy. A small volume of high temperature air has a higher “quality” than a big volume of lower temperature air, even if the total thermal energy is the same. This is why automotive engines tend to be less thermally efficient than stationary engines and powerplants- they’d have to be enormous to keep extracting heat from the cooling combustion products, which requires a bigger, heavier car, which requires more power, and so on. Since you have to use more energy to move that enormous mass it really doesn’t save you much fuel. This is also why you’ll often see race cars belching fire out the exhaust- they’re just using that first little bit of high-quality thermal energy to maxamize power output at the expense of fuel efficiency. Turbines are a relatively light and simple way to extract some of that marginal heat. Using them to compress intake air is a way to actually IMPROVE your power to weight ratio, so that’s why they’re used almost exclusively for that purpose. Still, they don’t actually generate boost that often and it’d be nice to extract power from that marginal heat all the time. A turbo alternator would probably be the way to go (especially in a hybrid) since it wouldn’t add any additional weight or complexity & would remove parasitic drag from the engine. The hard part though would be de-coupling the compressor from the turbine when you didn’t want to make boost. Perhaps the best way is to have the turbo ONLY power the alternatore, and then have an electric supercharger.