thoughts on Crower 6-stroke?

[payne171]

I went back and looked at the article to make sure I am not missing something, and I did pick up a few details. One, it implied that during light throttle cruise there was plenty of exhaust energy for the device, that it was the ideal situation to use the device. That is when you were concerned if it was any use because there was not enough exhaust energy. That is likely why we disagree. Furthermore, it described the TIGERS as using a waste gate to only operate under ideal conditions, primarily because a variable nozzle adds to much to complexity and cost to make it feasible. Your issue with it during less than ideal conditions seems to be valid, as it is bypassed. My gut feeling is that it will work, but bypassing it will take enough away from it that it cannot supply the whole car's electrical needs as implied in the article. The article did suggest that the switched reluctance generator makes it cheap enough that it can be worth it as a supplementary system, either to make smaller alternators viable or to add charge to a hybrid.

[serialk11r]

My argument isn't that there isn't enough energy, just not enough waste energy...
But I agree that this could be useful, it's something that should be implemented on all cars. Cars already need some kind of muffling, and accomplishing the muffling with a turbine that returns some shaft power back in the form of reduced alternator load is better than a restrictive muffler, or even an active noise cancelling system (which takes power).

I'm trying to say though, where you're going to see a potentially large increase in fuel economy is tapping waste heat. Currently, nothing is being done to capture waste heat. I believe it is the case that combustion efficiency improvements are nearing a dead end, and significant friction reduction can't happen without a fundamentally different design to the engine, so what's left to tap is waste heat. BMW's steam generation system produced double digit improvements in efficiency under some conditions, and it didn't touch the actual engine at all. Unfortunately thermoelectric generators aren't very effective and steam based systems have high weight penalty...but there's so much potential.

Glad we had a relatively civil discussion, another thread I posted in is going crazy

[Air-Hybrid]

Originally Posted by serialk11r

Currently, nothing is being done to capture waste heat.

Traditional turbos do capture waste heat (as has been said previously).
Turbo-diesels are a perfect example of this - where downsized engines give the same power for better FE.
If I dare bring Ideal gas law into this thread (it seems to add to arguments in the BSFC thread for some reason!), can I just confirm that we remember that decreasing the pressure of a gas, say by extracting work across a turbine, will proportionately lower it's temperature - by the IG law.

Originally Posted by serialk11r

My argument isn't that there isn't enough energy, just not enough waste energy... But I agree that this could be useful, it's something that should be implemented on all cars.

Isn't this a bit of a contradiction? (I'm not saying that to be rude. I'm just interested.)
I think the key is that, as you also say, all the big wins in IC efficiency are in the bag.
Regarding back-pressure on the engine, we know that none is bad and too much is bad. So I can't see why a well chosen turbine (non-supercharging) wouldn't remain within that sweet-spot of back pressure all the time. A handy effect of using a generator is that the ECU can determine the load (equal to back-pressure) second by second by wave-chopping the output.

Originally Posted by serialk11r

BMW's steam generation system produced double digit improvements in efficiency under [peak] conditions
...
Unfortunately thermoelectric generators aren't very effective and steam based systems have high weight penalty...but there's so much potential.

Cost to the manufacturer comes into this as well though.
The turbosteamer idea is probably around three times as complex as exhaust-generator-componding. And it would conservatively cost twice as much to integrate. So it would need to give a minimum of twice the mpg gain as the turbo-assist.
... which it might, but no one really knows yet.

[Air-Hybrid]

Originally Posted by payne171

My gut feeling is that it will work, but bypassing it will take enough away from it that it cannot supply the whole car's electrical needs as implied in the article.

I just had a thought that just because it can be bypassed doesn't necessarily rule out the chance to delete the traditional alternator.
A standard alternator has to be built I assume for the worst-case instantaneous electrical load - t'internet says a F150 has a 130amp alternator, that's one of the bigger alt's I guess, but even so that's 4 times less than the peak on this 6kW device.
The thing is, at tickover the revs in an older car will drop down and can even stall if lots of amps are drawn from the alt. (modern cars ECU will ensure revs stay more level).
So the same principle can apply here if the turbogen is properly integrated.
Of course it's less efficient to increase the output of the engine for more exhaust pressure than it is for shaft power but if you look at the full cycle of driving it's a better deal because you now have extra electrical energy longterm.

[maxc]

Why waste the effort and inject water when the heat in the cylinder is already out the exhaust!

[drmiller100]

Originally Posted by maxc

Why waste the effort and inject water when the heat in the cylinder is already out the exhaust!

danged good question.......

[oil pan 4]

Only problem is I dont think the engine could get hot enough and last long enough to generate the temperatures you need to get work from steam to expand fast enough to run a high speed engine. With steam piston engines you want real low speed, long stroke engines.

There are better combind cycle combos out there.

[user removed]

I checked the exhaust on my old Nissan Z car engine once. At idle it was not even 200 degrees. I think the amount of heat you need to "instantly" turn water into steam just isn't there after expansion of the combustion gasses. If your peak combustion temperature is 3300 degrees and it expands to ten times that volume, how much heat do you really have left over to make "instant" steam.
To get the expanison of the old high power steam engines you need steam at 1000 degrees and many times atmospheric pressure to be "superheated dry steam". I don't think there is enough resudual energy to do that "instantly".

regards
Mech

[drmiller100]

we can agree at cruising speed, the temperature is something north of 250 inside the combustion chamber.

If we can raise the mean pressure during the power stroke we will have "more" power.

I still think there is an opportunity to add wet steam during the intake stroke and end up with more "power" for a given amount of fuel.

[user removed]

Take an acetylene torch and move your finger past the flame very quickly. Not really but I have done that a few times, mostly accidentally. Since your body is 90% water if water could be Instantaneously vaporized, your finger would evaporate in the heat. In a running engine that is happening much faster than you could ever move your finger past a torch flame.
It takes a lot of heat to get steam superheated, the state where it really produces power. Magnitudes of more heat than to jsut bring it to a boil.
In 760 degrees of crankshaft revolution you may see that kind of temperature for less than 45 of 750 degrees.
Now an oxygen sensor needs considerable heat to function properly. How are you going to make steam without cooling the exhaust to the point where the O2 sensor is not functioning.

regards
Mech