thoughts on Crower 6-stroke?

[serialk11r]

At part load I think you'll be hard pressed to find enough power that can be converted, as I said already...
The difference between a turbocharger turbine and a turbine that is supposed to collect as much waste pressure as possible is a turbocharger creates a greater pressure drop in order to generate more power.

Accessories using 20hp? Maybe at full speed, full load, but again, normal driving happens at extremely low load and rpm, where there is almost no wasted kinetic energy in the exhaust to speak of. When you're at part load, there isn't enough pressure leftover in the cylinder when the exhaust valve opens to drive the accessories, but there is far more than enough heat energy. Say on the highway you are using 20hp. The engine running at part load is throwing away around 30hp in the exhaust (the number doesn't really matter that much, it's just important to note that it's greater than or equal to the amount of useful work you're getting and on the same order of magnitude, because the ideal cycle at lowered compression ratios dumps half the fuel energy into the exhaust, throttling loss goes into the exhaust, and cooling/friction loss goes on top of all that).

Say you had a pathetically small heat exchanger for cost/weight reasons, and a single stage turbine running at 60% of ideal efficiency which I believe is a bit below 70%. The turbine gives you back around 35% of the available steam heat energy after all conversion losses, and say the steam only carries away 10% of the available waste heat. At 3.5% conversion you are still getting over 1hp from the waste heat, which is enough to cover all the electrical loads plus a water pump and then some.

Although if I may note, the Subaru electric turbo is a great thing. A normal turbocharger is attached to the compressor, and has issues with transient response and such. The electric turbo breaks the turbocharger into 2 components, a turbine which only needs to absorb excess energy in the exhaust instead of creating backpressure for more shaft power, and a supercharger which can run off the battery for a short period to improve transient response. When you don't need the power, the engine behaves like a naturally aspirated engine with enhanced exhaust expansion via turbine

[Marc F.]

If your interested in "blowdown" turbines or energy recovery check out a Detroit DD15. One is in my truck and it use a turbine connected to the crankshaft running off the exhaust. They have been used in limilted numbers of engines. I dont know that it really helps the fuel mileage.

It separate from the turbocharger system to boost the engine.

I dont know much about the whole subject but I can tell you my old engine would pull down to 1250 rpm and you had to shift, this one will pull down to 1000 rpm before you have to shift. Mind you anything over 1500 rpm is a waste on this engine. (14 litres displacement) There is about 300 rpm between gears. Most truck engines operate in very low rpm range like this to get good mileage.

I think the turbine does help the low pulling power, I have never had on the pulls this low.

[Duffman]

It is not because it has turbo compounding that your engine will run slower, that is the current trend across all of the heavy truck engine manufacturers right now.

[payne171]

If you say so, serial. I'm sure you know more than the engineers who developed it. Try reading the article. I am not an engineer but it seems to me that if the turbocharging process was that inefficient, why would any passenger car have a turbo on it? You are talking about gaining maybe one horsepower; the article clearly stated that an exhaust driven switched reluctance generator could provide 6 kilowatts of power. You did read the article, right?

[serialk11r]

Yea I've read that article a long time ago.
I've done some calculations before on how much power you can get out of this. You know how the Prius has a longer expansion stroke? The Prius doesn't even see 10% higher peak efficiency than its non-Atkinson cycle engines. That's an ideal scenario for the waste exhaust pressure, to be able to expand it adiabatically with a piston. The moment you blow it out of an exhaust valve, you lose some of the energy, and having it go through a turbine makes you lose half of the energy too.

The key thing to note is that an engine doesn't consistently flow gas; Exhaust gases come out of the cylinder first in a "pulse" as the residual cylinder pressure blows the gas out, and then the rest of it is pushed out by the piston. Only the "pulse" is useful for producing work, the rest of the gas flow uses the piston's energy. Exhaust energy can be thought of having 2 components in some sense, the component that is "free", aka wasted energy that the piston did not absorb, and the component that comes from the piston pushing against the exhaust gas. A turbocharger uses both.

Turbocharging is very inefficient, but it is simple (practically "bolt on"), effective (we all know how much power turbo engines can make), and more efficient at full load than a supercharger. A supercharger uses 100% shaft power to create boost, while a turbocharger can utilize some of that "pulse" energy. The reason it is inefficient is because it is designed to produce as much boost as possible, not increase efficiency. To produce boost, the turbocharger dams up pressure in the exhaust, which requires engine shaft power to maintain. However when the exhaust valves are opening before the piston bottoms out, that extra "pulse" makes it to the turbocharger and imparts some extra work. A well designed turbocharger has more boost pressure than exhaust backpressure, which means it is utilizing those "pulses".

Another reason to turbocharge is that despite being less efficient, downsizing the motor improves part load efficiency simply because you have to use more of the available power and because the smaller engine has less losses.

I'm not saying that this is a bad idea or that it doesn't work, just that under most driving circumstances it does not represent a big efficiency increase over a belt-driven alternator. For peak power, it can generate an appreciable amount of extra energy, as they are doing with F1. You don't need to be an engineer to see that energy doesn't come from nowhere.

You did read my previous posts right? I explained it pretty well IMO...

[Air-Hybrid]

All these claims of efficiency being poor or not, are all very entertaining, but perhaps the claims one way or the other could be substantiated by, oh I don't know, some actual data or links, etc.
Saying a turbocharger is 'very' inefficient or that, 'say 10%' of this power or that is recovered/lost/pulled-out-of-a-hat remains just rhetoric until figures are offered up or failing that extrapolated.

I don't suppose the TIGERS inventors have given figures on differing load efficiencies or back-pressures, but the shaft power for a standard turbo should get us some of the way there I would have thought.

[payne171]

At some point, common sense has to play a role in your thought process serial. You dismissed a technology based on a few calculations made after reading the article. At least one of the engineers on the project was listed as a doctor; don't you think he is capable of those same calculations? You are talking about maybe gaining one horsepower as being feasible, but a device that can put out 6kw isn't? I am sure it won't put out as much power at light load, but that is fixed with more battery.

Come to think of it, look at your own post. A turbocharger is more efficient than a supercharger because it uses exhaust energy instead of crankshaft energy to power the forced induction. Why does that efficiency difference suddenly disappear when one uses exhaust energy to drive a generator instead of the crankshaft?

[user removed]

Ford new 1 liter ecotech engine is a great example of how to use a supercharger or turbocharger to increase overall engine efficiency. In the less than 1% scenario when you need extra power, like merging on the Interstate, you have the burst of power, instead of having an over sized engine running at lower efficiency all of the time except when you are rapidly accelerating.

Consider the size and power of the average 18 wheeler compared to the engines power and torque. Combine that with the aero drag of a big ring and the mileage they can get is many times better than any passenger car if you factor in the amount of mass they are moving and the aero drag they have to deal with.

regards
Mech

[serialk11r]

Originally Posted by payne171

At some point, common sense has to play a role in your thought process serial. You dismissed a technology based on a few calculations made after reading the article. At least one of the engineers on the project was listed as a doctor; don't you think he is capable of those same calculations? You are talking about maybe gaining one horsepower as being feasible, but a device that can put out 6kw isn't? I am sure it won't put out as much power at light load, but that is fixed with more battery.

Come to think of it, look at your own post. A turbocharger is more efficient than a supercharger because it uses exhaust energy instead of crankshaft energy to power the forced induction. Why does that efficiency difference suddenly disappear when one uses exhaust energy to drive a generator instead of the crankshaft?

I never said it disappears, I just said I highly doubt 6kW is possible under light load. On the highway your car could be producing as little as 10kW of power (small car, 60mph), what makes you think there is 6kW that can be obtained for free from the exhaust? Consider that at full volumetric efficiency, almost 90% of the available energy in the gas is converted into shaft power by the piston. Energy that isn't there ISN'T THERE. Turbines can NOT capture thermal energy. When I give estimates for efficiency, I use upper bounds, so the percentages that I'm calculating are not just numbers pulled out of my ass, they are a reasonable upper bound for the efficiency. Upper bound, meaning the actual efficiency can't be higher.

Might I also mention, turbochargers can be less efficient than an equivalent shaft driven centrifugal supercharger under some operating conditions, when the turbine is causing excess restriction. Turbochargers were never an efficiency thing, they are an easy way to get more specific power. The reason it's getting popular is downsizing an engine is the easiest way to get part load efficiency improvements, and these typically outweigh the overall efficiency loss of a turbocharger.

It is a fact that the theoretical efficiency of a single stage turbine cannot exceed a certain percentage of the ideal efficiency. When you stick a turbine in the exhaust, the only free energy you can pick up is energy that comes from momentum transfer of the exhaust gas. If you actually go analyze the physics instead of tell me that some engineer or Ph.D. said something, you might get something out of this. You don't need to be an engineer to understand the physics behind an engine. Stop using my supposed lack of credentials to attack my point, it's not doing anyone any good.

I already gave one figure, in F1 they were able to recover 7% more energy at full load. At part load this number invariably goes down.

The technology has a place, it can reduce noise emissions of vehicles, and it can improve efficiency by a small amount under high load circumstances. This is a great thing, but we need something else for part load efficiency improvement.

[payne171]

If the engine is producing so little power as to not be able to turn the turbo enough, how is it going to produce enough steam to do anything of use. I don't know if it could do the job, but I stand by my original statement that it could do it better than steam could.