Increasing efficiency - converting heat?

[beef_bourito]

oh yeah, i live in the greatest nation on earth but we had our thanksgiving day in october (im talking about canada)

Anyways on the subject of redesigning the whole engine, piston engines only produce power on one stroke per rotation per cylender. if you use something that uses more like a rotary or a quasiturbine you get more efficiency because there isn't the added resistance of those extra strokes.

also the limiting factor on the power of a piston engine is how fast you can accelerate the internal parts (whether positive or negative acceleration) because you have to accelerate it up, negatively accelerate it up (deceleration) then accelerate it down. this reduces the efficiency. one other thing is you could use a turbine engine, these are constantly turning and you don't need to change the direction of parts, you just need to apply a force in one direction (well a circular pattern but you get the idea).

you could also have a hybrid, an engine that charges betteries and it moves with electric motors. this would remove the inefficiency of acceleration because the engine would be running at a constant speed. turbines are not very efficient on acceleration but very efficient at a constant speed so they are perfect for this. also you don't need stuff like valves, cooling (well you need lubrication and you might need cooling for that but you don't need water cooling), or any of that stuff in a piston engine, turbines are very simple and very efficient. best of all, they run on basically any fuel, propane, gasoline, diesel, kerosene, etc.

a classmate and I are working on a science fair project to build a turbine engine and measure which fuel produces the highest thrust, rpm, temperature, etc. Ill keep you guys posted on our progress, it might be slow because i go to a boarding school but I think it should be interesting.

[Jayslay420]

Ok guys, I appreciate all of your input. If you checked my profile you already know I already run a turbo on my car. The idea's I am trying to generate on this thread are new ideas, not everything thats currently available.
I was thinking again, about the design problems that might occur with a STEAM powered turbo perhaps? What if you had a long boiler that coupled to your exhaust systems piping and or the radiator? Could this steam activate a turbo?
This may sound silly, but I really want to push the boundaries here, and incorporate all your combined knowledge into my research. Any opinions on what I've suggested?

[drew300]

Many years ago I read of flowing the coolant the other way around the engine - coolest to the head, so you can raise compression, and then warmer coolant at the cylinder walls for less condensation. It was supposed to work, and I believe one of GMC small blocks does it this way. Also, the Japanese have "direct injection" gasoline engines. By directing the fuel into the combustion chamber directly, you cool the mixture, which again allows higher compression. I'm told our fuel will be clean enough to consider this in a few years. And I just remembered, BMW has a variable valve system that allows them to remove the throttle valve. This reduces pumping loses.
Btw: a steam powered turbo? Can you imagine the turbo lag first thing in the morning? (in winter) But an interesting idea.

[Jayslay420]

Yeah, the lag during the exhaust heating would be substantial, thusly a good reason to run dual turbo type setup. The steam driven turbo would only activate at ideal operating temperature. This would however absorb some of the "wasted" potential present in the radiated heat.

If large portions of gas are wasted in heat, I see this as an easily accessible source of energy. Just because it hasnt been done doesnt mean it cant.

Anyone else see some potential in my idea?

[zagrot]

i just heard one that is kindof off the wall, but interesting. modify an engine such that half of the cylinders burn fuel, and the other half recieve the exhaust gasses to push the pistons downward. esentially the exhaust of one cylinder is directed into the intake of the next cylinder in the cycle and when the "driven cylinder" reaches bdc the exhaust valve for that cylinder opens so the exhust gasses are not compressed on the piston's upward stroke. i don't know how viable the idea is, but i just spoke to someone who brought it up and thought it would make a good conversation piece.

[Moppie]

Have you seen how big steam powered engines tend to be?
And how much fuel they have to burn to generate enough heat to boil enough water to produce useable power?

[beef_bourito]

the problem i see with that idea is the extra moving mass. if you have a v8, half of the cylenders run on exhaust and he other on fuel, you're trying to turn the mass of a v8 with the power of an inline 4. maybe if you were to use smaller cylenders with lighter parts it might work but i don't think so. it's a good concept but i think a turbine would be a more feasable use for exhaust gases because you're not forcing anything to change directions.

And a turbo doesn't add eficiency, in theory it should but it adds exhaust backpressure that makes the engine work harder, also it adds air and fuel so you're burning more fuel per stroke.

[Jayslay420]

Originally Posted by Moppie

Have you seen how big steam powered engines tend to be?
And how much fuel they have to burn to generate enough heat to boil enough water to produce useable power?

Ya but I corrected my idea into a turbo, certainly alot easier to turn then a full block engine. As I said before the turbo is an assesory one in a dual turbo set up.

The fuel is the exhaust gas, heating a relatively small amount of water. Your fuel is basically the gas that you put into your engine but is wasted as heat. Right?

Anybody that understands what I'm saying, please give me pointers.

[Moppie]

I understand, but what your missing is that to produce enough steam, with enough heat and pressure to be useful it has to be heated under pressure in a Boiler.
A boiler is heavy.
To produce enough steam to be of any use it would take more heat than the exhaust is capable of producing.
You might, be able to build a very small boiler that was able to extract enough heat out of the exhaust to run a very small turbine that produced enough power to run your indicators or dash lights.
But then what would be the point?
You would still need an alternator to produce power for the rest of the cars electrical system, and your boiler/turbine assembly would still be so big and heavy that it have a negative effect on the cars performance, safety and looks.
And of course a modern exhaust system needs to be operating at a high temprature in order for the Catalytic converters to work.
By useing the exhaust heat to boil water you would also be cooling the exhaust.

Steam power is big and heavy, and best suited to stationary engines

[curtis73]

Plus, lets not forget that every time you ask energy to change phases or transfer from one substrate to another, you lose some of it. Its better to just use the exhaust to directly power the turbo instead of extracting some of the energy from the exhaust into water to then power the turbo.

The five main problems I see with designing a steam operated turbo go like this... and PLEASE forgive me for the long post. Its 11pm, the wife is asleep, and I have no life

1) lag if you make it direct to turbo. If you ask the water to make steam as you require it, the lag will be incredible... like on the order of 5 minutes. If you think about gasoline exhaust at its absolute hottest, your talking about 1800 degrees F, or about the same as an electric stove on Hi. It would take quite a while to get steam.

2) storing steam if you make it indirect. The other way I see is using a boiler like Moppie the Dirty Hippie said. The issue then becomes how to store a boiler on board a car and keep it hot enough to have steam on demand. Not to mention, getting the water hot enough to generate steam might take 30 miles or 2 minutes depending on how much water you have in the boiler.

3) storing all the water. Even if you effectively design the system to work properly, it will take a pretty good volume of steam to operate it and I can't imagine 10 gallons of water lasting as long as 10 gallons of gas on a spirited Sunday drive.

4) how to control the steam if its stored. If you have a boiler with steam, you need an entire system to modulate how much steam and how much the turbo sees based on where your foot is. You would also have to make sure the controller compensates for the temperature of the water. On a cold morning when you first start out to work if you floor the throttle while the water is still 40 degrees, the ECM needs to know that the turbo isn't going to magically produce 10 psi like it did last night when you shut down.

5) The boiler will probably have to be metallic to be able to transfer heat of that magnitude. The water will need to have some way of staying liquid when the temps drop below freezing. So, you need to have something dissolved in the water to lower its freezing point. Anti-freeze won't do since Ethylene Glycol and Propylene Glycol will evaporate at about 360 degrees. Once the water is gone the glycols will start boiling. Plus, you would have to start with at least 40% glycol meaning that of your capacity for water, only 60% can be used. In addition, as the water evaporates and you approach the 40% volume mark, the amount of available steam will drop off. You wouldn't get full pressure all the way until you're out of water, you would slowly lose available steam. A common way to combat freezing is by dissolving a disassociative ionic substance in water like NaCl; table salt. The problem is that their ionic bond is what makes the water not freeze, and it also give the water incredibly higher electrolytic properties that will erode even the best stainless steel in short order.

NONE of this is to say that its not possible, especially since you've given it much thought and I just jumped in. I'm interested to hear what you have in mind. I can see two sides here. A typical turbo uses exhaust heat and flow to generate energy, but the bottom line is that it only recovers a fraction of the heat. I can see that an exhaust-to-water intercooler could effectively remove much more heat from the exhaust and store it as steam than a typical turbo, but I'm not sure that you can effectively get the energy back out of the water into a turbine without compromising the design of the car. I guess what I'm saying is that your idea is thermodynamically sound. There is a lot of energy wasted in the exhaust. A turbo recovers some of it, but you could get a lot more heat if you absorbed it into water... its just that I can't see that storing it as steam or hot water would be very effective in an automotive application.

[Jayslay420]

Alright guys, you've given great insight. I see some of the downfalls of this system from a new standpoint. You boys got some experience that I just don't got right now. I've thought about what you've said and think its time to go back to the drawing board. No way a full boiler system would be effective, that is for certain. I do have some follow up thoughts.

A)Would the steam from a substance with a lower boiling point such as ethanol or methanol produce steam at a lower temperature? Is this a viable alternative to my theoretical water steam turbo?

B)Everyone says there is not enough available energy, when this simply isnt true. If 75% of my gas is used in my engine to produce cranking power..then who's to say the remaining 25% has limited usefullness such as running dash lights. I understand the losses when converting types..this whole project is trying to find a way to efficiently use this lost power. No way around it, 25-40% potenital energy has got to be able to run more then dash lights.
I understand the whole catalytic process uses the heat..too bad my car isnt running one. This wasnt ever really considered when I was thinking about the idea. Good point though indeed.

[curtis73]

Originally Posted by Jayslay420

A)Would the steam from a substance with a lower boiling point such as ethanol or methanol produce steam at a lower temperature? Is this a viable alternative to my theoretical water steam turbo?

Yes, but who wants an incindiary vapor at high temperatures hanging around in their car? Big booms happen that way.

You are correct that even with turbos there is a considerable amount of heat wasted out the tailpipe, but I'm not sure that water/steam is the best way of harnessing it with current technology.

How about a regular turbo for the normal power adder, but also a turbine-driven alternator? That would remove the drag associated with a belt-driven accessory and make more use of the exhaust heat. You or I with a lead foot would have no trouble keeping the batteries charged, but you might have trouble if a grandma buys the technology. She'd never have her foot in it enough to spin the alternator.

[Moppie]

Drive the alternator of the end of the Turbos compressor wheel.
Could be interesting, your removing the loss from the belt drive, but creating turbo lag and powerloss under high electrical load. Turn the Lights on and lose 5psi
Crank up the stereo and blow your turbo



What you need is a head activated electrical engery generating chemical reaction that will last for several hours and reset itself when the heat source is removed.
Then you could use it power an electric motor etc.

[beef_bourito]

you could have a blet driven and exhaust driven alternator, you have the belt with an electric clutch that only connects when you don't have enough electricity running on exhaust. when the batteries are fully charged, it only runs on exhaust.

[drew300]

Jayslay, did you make a fundamental eror, or did I read you wrong.
A standard Carnot cycle gas engine is about 20% efficient. That's 80% out the rad, tailpipe, etc.
Diesels are about 30%, with gas turbines up around 40%.
I've read that an efficient, modern coal-fired electrical plant runs around 25%.
Yes, there's lots of waste heat around.
A WW2 Spitfire (aircraft) did a couple of interesting things with waste heat. The stubby exhaust pipes were fashioned so that the exhaust added about 70 hp to the airframe as thrust. As well, the radiators, under the wing, heated (explanded) air, so that when it left the rad housing, it was accelerated and created enough thrust as to cause no drag, sort of like a ram-jet. Unfortunately, non of this applies to a car.
Thermo-couples are simple units to make electricity from heat. They can be as simple as iron wire and copper wire twisted together. But it takes a lot of them to get much power.