General Question

FireMadeFlesh's avatar

Would this engineering concept work?

Asked by FireMadeFlesh (16563points) October 6th, 2014

I read once that the reason behind the modern trend in cars of engine downsizing in terms of cylinder count is thermal efficiency. A 3.0L V8 will lose more heat than a 3.0L V6, all else being equal, because it will have a greater total cylinder surface area. Because more heat is lost, less chemical energy is being converted into kinetic energy, efficiency is lower.

So why not use the heat given off by the engine to generate further power? What if the water jacket, which is already built into the engine for cooling, were hooked up to a small steam turbine, which would then be used to charge batteries as part of a hybrid set up? F1 this year is already using the MGU-H to recover heat energy from the exhaust, so why not recover engine heat also? Is there a reason why this may not be a practical solution?

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31 Answers

stanleybmanly's avatar

Well you face the problem of generating steam from the coolant. Don’t forget that it is the engine through the agency of the water pump which circulates the coolant. Using the coolant even in the form of steam to turn the blades in the turbine actually means that the water pump is in effect driving the turbine. More energy loss. There’s no getting around the second law.

jaytkay's avatar

Using the coolant even in the form of steam to turn the blades in the turbine actually means that the water pump is in effect driving the turbine

No, the pump is not driving the turbine.

Instead of warming the air surrounding the engine and radiator, the heat is retained to make steam which drives the turbine.

stanleybmanly's avatar

Is the temperature of the coolant at its hottest sufficient to create a reliable head of steam? If so, aren’t you going to have to insert a boiler somewhere along the line?

CWOTUS's avatar

The primary driver behind most automotive design is not pure engineering for its own sake, but a collection of various “market factors”. One primary market factor – not necessarily a driver of the “free market” (to the extent that that exists anywhere in the world) – is a thing called CAFE. CAFE is an acronym that stands for Corporate Average Fuel Economy; it’s a regulation imposed by the Federal (US) government that attempts to mandate – ahead of “normal” market forces of consumer demand for various products – that automobile manufacturers selling in the US market make vehicles for their various classes of offerings (compact cars, mid-size sedans, SUVs, pickup trucks, large trucks, etc.) that have average fuel economies that meet criteria set by the regulators.

Since most car makers around the world want to sell into the US market, that means that the US federal government dictates what many manufacturers will produce and sell around the world.

In other words, despite what you may want as a consumer, before you even appear in the showroom the manufacturer has been told – by the feds – the ranges into which his offerings must fit. Since CAFE standards for fuel economy have been gradually increasing over time, forcing manufacturers of passenger cars especially to produce more and more fuel-efficient vehicles, manufacturers have generally turned to more efficient 4— and 6-cylinder models simply to meet the miles-per-gallon targets.

Once the fuel efficiency targets have been met, the manufacturers have to work within pricing guides set by their own marketers to make vehicles that will sell for prices that people are willing to pay. While there may be all kinds of great engineering schemes that would coax more and more efficiency (miles per gallon) out of the liquid fuels that we use, there is a practical cost limit to what can be afforded – and what will be paid for.

Most consumers would opt not to pay the cost of a vehicle such as you propose; it simply wouldn’t sell. Even if a handful of people would pay that cost, the manufacturers have to make vehicles by the hundreds of thousands per year to take advantage of the economies of scale that have made them household names in the first place. They won’t build it.

That’s if it’s even practical. I have a sense that even if the engine you propose were technically feasible (and I have strong doubts about that), it would not be advantageous when the cost of routine maintenance and repairs are factored in over the expected life of the vehicle.

Finally, since diesel engines are available in the US market to propel attractive, comfortable and practical passenger vehicles (I had a ride in a diesel-powered Volkswagen Passat last week that gets upwards of 40 miles per gallon), one might ask “Why doesn’t everyone drive that car or one like it?” You can probably answer that yourself: Not many consumers will elect to pay an additional 30%-50% premium on a vehicle that will save them money in the long run when they can spend less money right now for a machine with the same look-and-feel.

jaytkay's avatar

I found a couple of existing devices.

“A [BMW} turbosteamer…uses a steam engine to convert waste heat energy from an internal combustion engine into supplemental power for the vehicle…The steam circuit produces 14 hp…”
Wikipedia – Turbosteamer

“An automotive thermoelectric generator (ATEG) is a device that converts some of the waste heat of an internal combustion engine (IC) into electricity using the Seebeck Effect.”
Wikipedia – Automotive thermoelectric generator

Tropical_Willie's avatar

Combine cycle power plant is usually Gas Turbine based. It uses the residual heat to heat water for steam for additional power.

ARE_you_kidding_me's avatar

In a vehicle added weight and complexity are not usually good things. Modern V8 engines actually operate with comparable fuel mileage to V6 engines. A couple of easy additions would be a handfull of pelltier devices to generate small voltages for things like lighting and ease the running load on the electrical system. The electrical systems in cars could be much more efficient. That increases the price on something most Americans can hardly afford anyway though.

rexacoracofalipitorius's avatar

Having steam in your cooling system is widely considered a Bad Thing. Automotive cooling systems are designed to keep the water mixture in its liquid phase, because the liquid can’t have a temperature higher than its phase-change temperature (because additional heat goes to the phase change until the change is complete.) The system is under pressure, and if the temperature rises enough (about 280 F or so) it starts venting pressure in order to release heat. Thus there’s a multi-layered system in place to keep the temperature stable below 300 F. Temperatures higher than that are unhealthy for Otto cycle engines, which have lots of parts with small tolerances that can’t deviate from each other too much without making the engine unhappy.

Also, more cylinders is not fundamentally less efficient than fewer cylinders at the same volume, and particularly not for the reason you mention. This is because cylinder volume and cylinder surface area don’t change at the same rate.

The surface area of the cylinder is described by (π*d)s, where d is the diameter of the bore and s is the length of the stroke. If you change the volume (π*(d/2)^2*s) by changing the stroke, then the change in the surface area of the cylinder (the area where friction can happen) changes linearly with the change in stroke length, because the factor πd stays constant and d changes by a single factor. If you double the stroke, you get double the surface area. Thus, if RPM stays constant, you should get the same amount of friction.

If you increase the bore diameter, you get a larger increase in volume than in surface area. This is because the increase gets squared and multiplied by pi each time.

Here are some calculations I made on a spreadsheet. Because Fluther doesn’t support tables (or a code tag, or lots of other useful stuff), it probably won’t look very nice.

bore radius || stroke length || volume || surface || change in surface
7.9788456080 05 1000 79.7884560803 0
5.6418958355 10 1000 112.8379167096 33.0494606293
4.6065886596 15 1000 138.1976597885 25.359743079
3.9894228040 20 1000 159.5769121606 21.379252372
3.5682482323 25 1000 178.4124116153 18.8354994547
3.2573500794 30 1000 195.4410047612 17.0285931459
3.0157201755 35 1000 211.1004122822 15.6594075211
2.8209479177 40 1000 225.6758334191 14.5754211369
2.6596152027 45 1000 239.3653682409 13.6895348218

radius stroke volume surface change in surface
5.6418958355 05 500 56.4189583548 #VALUE!
3.9894228040 10 500 79.7884560803 23.3694977255
3.2573500794 15 500 97.7205023806 17.9320463003
2.8209479177 20 500 112.8379167096 15.117414329
3.9894228040 05 250 39.8942280401 -72.9436886694
2.8209479177 10 250 56.4189583548 16.5247303146
2.3032943298 15 250 69.0988298943 12.6798715395
1.9947114020 20 250 79.7884560803 10.689626186
2.8209479177 05 125 28.2094791774 -51.5789769029
1.9947114020 10 125 39.8942280401 11.6847488628
1.6286750397 15 125 48.8602511903 8.9660231501
1.4104739589 20 125 56.4189583548 7.5587071645

yep, it’s a mess. Oh well. I was going to say more things, but I give up.
I’m pretty tired of fighting with this website!

FireMadeFlesh's avatar

@stanleybmanly The idea is that the turbine replaces a traditional radiator, or at least allows the radiator to be much smaller, as less heat is required to be dumped into the atmosphere. The turbine wouldn’t be driven by the water pump, because allowing the coolant to evaporate at a particular point in the system would create a pressure gradient.

@CWOTUS Good points, but as the restrictions get gradually tighter, will it not become necessary to draw energy from every available source, to make the most of each drop of fuel? Diesel cars are great, and Mercedes’ new Diesotto series of HCCI engines promise to be even better. But all internal combustion engines produce heat, so why not combine this system with a diesel also? The development cost is a big issue also, but people are still buying hybrids despite the price premium in some segments (the new Audi A3 hybrid vs. S3 being the example that springs to mind).

@jaytkay and @Tropical_Willie Thanks for the links, I’ll take a look when I have more time.

@ARE_you_kidding_me Can you please provide an example?

@rexacoracofalipitorius I’m going to have to come back to your answer. It’s going to take a bit of thinking to respond comprehensively.

jerv's avatar

The simple answer is that steam turbines are complex enough to drive up the cost by more than it’s worth for the relatively small gains. However, there’s a reason VW is ditching naturally aspirated engines in favor of smaller turbocharged ones; the same reason many diesels are also turbocharged.

@rexacoracofalipitorius The @ sign can be your friend;
I know you love monospace fonts ;)

FireMadeFlesh's avatar

@jerv Fair enough. A lot of this question is just the sentimentalist in me trying to find a way we could return to the great engine formats of days gone by. I love Koenigsegg’s research into electronic valve actuation, which could do away with camshafts altogether. It’s a bit of a pipe dream, but it would be nice if such technologies could allow us to extend the life of naturally aspirated, high revving masterpieces such as the current Ferrari 4.5L V8 without recourse to forced induction.

rexacoracofalipitorius's avatar

@jerv I don’t understand what you mean: I didn’t use the @ in my original response because I was answering OP. If you mean that @ can somehow make monospace markup, then I’m sure you’re right, but since it’s not documented anywhere and I’m obviously not one of the Cool Kids, I guess I won’t be using it.

@FireMadeFlesh What’s so bad about forced induction? It’s hard to do properly, but when properly done it’s hard to beat. IMO an engine without active induction is only half an engine. There’s nothing about classic old engines or fancy new valve actuation that makes extra compression a bad idea.

jerv's avatar

@rexacoracofalipitorius I didn’t know about that one for years myself.

The great engine formats of days gone by? They went by (or rather, bye-bye) for about the same reason we don’t use wood-spoked wheels rimmed with metal; they were superceded by more advanced technology. High-revving engines take more precise balancing, which in turn drives up cost. That’s less important for a $200k-2.5m supercar,but is a real concern for $25k passenger cars.
Also, there’s relatively little R&D needed for forced induction. It’s a mature technology, thus financially feasible for mass production.
The net effect of a turbo is to take the energy of the exhaust that would normally just be wasted and use it to make more power. Why have a 350-pound 100hp engine when you can take a 275-pound 70hp engine, add 25 pounds of spinny-muffler action, and get 120hp? Or, if you keep your foot out of it, an extra 10–20% MPG. We already have a way to harness the waste energy of an internal combustion engine to spin a turbine.

Bill1939's avatar

@FireMadeFlesh perhaps using a Stirling engine to generate electricity would help accomplish what you want. (see)

jerv's avatar

Too bad we don’t have really powerful thermocouples. Turning heat directly into electricity with no moving parts would be great for hybrids; use the waste heat of the combustion engine to help power the electrical side of the powertrain…

Sadly, thermocouples tend to put out milliwatts; most are useful as sensors, but that’s about it. Well, that, and the idea is already patented so there would be legal issues as well.

CWOTUS's avatar

If you’re into new technology, @FireMadeFlesh, that is, technology that already exists and is being developed for commercial application right now, then check out the Duke Engine. I look forward to having that in a vehicle someday while I’m still driving.

Bill1939's avatar

@CWOTUS when I watched the the Duke Engine video I was reminded of an article that I have saved for 48 years. In the February 1966 issue of Poplar Science monthly the cover story was about a “Tiny Steam Auto Engine” that used axial movement. The prototype Gibbs-Hosick Elliptocline steam engine had seven cylinders, a 14.1 cubic inch displacement, weighed 60 pounds and produced 30 horsepower at 1,360 rpm (“one critic says it looks like a metal oatmeal box lying on its side”).

FireMadeFlesh's avatar

Thanks all, I’ve learned a great deal from this thread.

@rexacoracofalipitorius and @jerv I realise that forced induction has many benefits. It is a mature technology, greatly improves efficiency, and makes many technological gains in naturally aspirated engines even better. But I still can’t help but feel that turbocharging removes some of the emotion from an engine through removing the incentive for a high revving engine and suffocating the sound. And turbocharging is considered to be superior to supercharging for efficiency, with only Jaguar and Dodge bucking the trend with their supercharged performance engines. While I’ve been deeply impressed by the lack of lag in some of the modern hot-hatches I’ve driven, they still don’t have the response of my car’s rev-happy naturally aspirated engine (which, incidentally, was killed years ago by Euro V). The low end torque also negates the need to explore the higher rev ranges even in cars like the new BMW M4 that do still rev. Ferrari has dealt with that in quite a novel way in the California T, and hybrids like the McLaren P1 and BMW i8 have effectively eliminated lag, so I guess my argument rests on the sound. Which of course is no reason to ignore the great benefits offered by turbocharging, but I’ll always miss this sound.

Still, if turbocharging can assist the comeback of the Wankel Rotary engine, I’ll be a happy man.

Tropical_Willie's avatar

@FireMadeFlesh The Ford EcoBoost engines use small turbochargers with fast spool-up speeds, they also have an Engine Management system that bleeds off a lot of the pressure at the waste gate starting at a lower engine speed. This allows the engine to have higher torque at lower speeds and the torque stays flat through the whole RPM range. The boost pressure is more constant rather than increasing with higher engine RPM’s.

FireMadeFlesh's avatar

@Tropical_Willie I’ll be very interested to drive the new EcoBoost Mustang when it arrives here next year some time. It could be great. I should add that it really doesn’t bother me that VW Golfs and Nissan Pulsars are adopting forced induction. But I shed a metaphorical tear when I heard that Ferrari will turbocharge all its future V8s, and I hope the rumours of the Porsche Boxter and Cayman moving to a V4 turbo platform are incorrect.

ARE_you_kidding_me's avatar

@jerv we do, they are peltier devices and you can get useable amounts of current with them. The idea of a thermopile is not new, been around for centuries.

jerv's avatar

@ARE_you_kidding_me I forgot about those; I guess the brain is a little foggy near bedtime! Still, 14W isn’t really “usable amounts”, at least not for propulsion. Maybe to supplement the alternator…

@FireMadeFlesh I’m too pragmatic to sacrifice power, efficiency, and more just for sound. If I want “wub wub”, I’ll crank up some dubstep. If I want RPM, I’ll go gas turbine. I prefer engines with a wide powerband over peaky noisemakers that need a 6:1 final drive ratio. There’s things that are cool as occasional entertainment that just aren’t practical for daily drivers.
That said, I do like the Renesis engine; same power as the old twin-turbo RX-7s without the turbo. And the 120hp/liter all-motor S2000 is a nice toy, but I’m not sure I’d want one unless I was in a position to have a garage like Jay Leno’s; huge, and full of toys.

ARE_you_kidding_me's avatar

@jerv Large ones built right into the block and cooling system could yield significant, useable power. More significant gains would be to simply shave the power consumption of the electrical system itself though. Automakers are cheap and it’s disgusting how cheap and inefficient the electronics in automobiles are.

FireMadeFlesh's avatar

@jerv That is true. I can afford to focus more on toys than daily drivers, since I walk to work and drive less than 10,000km per year. I prefer my cars to have some emotion, rather than purely being a mode of transport.

jerv's avatar

@ARE_you_kidding_me How many kW are we talking here?

@FireMadeFlesh I drive ~17,000 miles/27,000 km a year just commuting to/from work, not counting any other trips I might make. I like cars with personality too, just not ones with annoying personalities. I spend enough time driving that I need to get along with my car. I love my little skull-car with it’s go-kart handling.
But as @rexacoracofalipitorius could tell you, I’m quite fussy about sound; the sounds you like hearing from an engine are ones that will never come from any car I would willingly own… or even spend much time within earshot of. It’s a matter of personal preference, and I prefer to limit my exposure to high-revving machinery with it’s high-pitch whining and wince-inducing harmonics to the ten hours a day that I’m listening to a 22,000 RPM cutter going through metal.

FireMadeFlesh's avatar

@jerv I can certainly understand why you’re sick of high pitched sounds then. I spend my days with screaming children, which can be quite ear splitting also, but I like my engines to have a rising tide of anger through the rev range. Are you more in favour of a baritone rumble such as AMG’s finest then? Or the whistles and bangs from a McLaren 3.8?

jerv's avatar

@FireMadeFlesh Before I answer that, let me tell you a little about how I hear the world when I’m driving. Tires make noise as they roll down the road, and road conditions alter the sound. In the winter or rain, I can usually hear a skid/hydroplane before I feel it. And since I’m between all four tires, I hear the sound from four different directions… but not always all the same sound, so they don’t always blend together into one sound. I hear the wind rushing over the car, but it doesn’t blend in with the road noise. Vent motors are never silent, and dash vents hiss in a different register from the air rushing around the outside of the car. I’m already hearing six different sounds from seven different directions.

So it shouldn’t come as a shock that I prefer a dull purr just loud enough to know my RPM without looking at a tach, but quiet enough to drown out with the radio if/when sensory overload kicks in. That said, many cars have too much sound dampening and/or too quiet an exhaust, and without those audio cues, being behind the wheel seems more like playing a video game than actually driving.

Aside from the ability to judge RPM without a tach (and thus know when to shift), all I want from the engine is pure accelerating force. Not power, force. People buy horsepower, but they drive torque. ;)

FireMadeFlesh's avatar

@jerv Interesting perspective – few people pay that much attention to their driving. I rarely play music in the car unless I’m driving a long way on cruise control for similar reasons. But while I like to be able to hear the tyre rumble for the sake of being in tune with the car, I can’t say it is an enjoyable experience for me in the same way the mechanical sounds of an engine are.

jerv's avatar

@FireMadeFlesh It’s not intentional; I just can’t filter things out very well. Especially not sensory input.

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