thoughts on Crower 6-stroke?

[serialk11r]

I advise you to think about the thermodynamics. It will make sense.

Even at part load, the exhaust gas is at quite high temperatures. If you had a frictionless, adiabatic Otto cycle engine with valves that had no restriction, the efficiency would be what you can find on Wikipedia for example: 1-1/CR^lambda. Computing this for typical compression ratios gives a bit over 60%. So what does this mean? It means that 30-40% of the fuel energy would be rejected to the exhaust under ideal conditions. In a real engine some of the heat is absorbed by the cooling system before this can happen, but exhaust gas temperatures under full load can be well over 700C, in fact I think catalytic converters are built to tolerate 900C for short periods of time or something. You can look up charts used for engine development that show exhaust gas temperature vs. load. Anyways about 20-30% of the fuel energy is expelled out the exhaust at temperatures over 400C even at part load.

Perhaps the best comparison would be this, an Atkinson cycle engine vs. Otto cycle engine at the same intake volume, with same compression ratio. The Atkinson cycle engine with full expansion will have zero excess pressure left. The difference in the work done by the Otto cycle and the Atkinson cycle is the work that can be extracted by adiabatic expansion of the gas to atmospheric pressure. Usually the gas leftover in the cylinder is at 3-5bar pressure when the exhaust valve opens. So how much energy can you get out of this? If you go run the calculations, you'll see that it's under 10% of total power. Yet there is about 50% of total power going out the exhaust in the form of heat energy.

A real life example: the 2ZR-FXE has lowest BSFC of about 220g/kWh. The 2GR-FSE, which has a somewhat shorter intake cam (thus higher throttling losses) has a lowest BSFC of slightly under 230g/kWh. 4% difference in efficiency. By contrast, the older, lower tech 1MZ-FE which had a similar "wasteful" intake manages 237g/kWh, still under 10% worse than the 2ZR despite having an older design with less efficient combustion. So under ideal scenarios, you can't get more than single digit improvements in efficiency just with a turbine, at full load. However regenerating the heat alone even at poor efficiencies stands to make a larger gain at part load, where there is less pressure wasted but still a lot of heat wasted.

Hope that explanation helped.

[payne171]

And at 400C, isn't exhaust manifold pressure going to be almost 65% over atmospheric pressure?

[drmiller100]

you guys are making it too complicated. a ROUGH general rule - 1/3 energy of the gasoline goes to work, 1/3 goes to radiator, and 1/3 goes out the exhaust as heat.

The exhaust side of turbochargers work primarily becuase of HEAT, not pressure. The ENERGY in the exhaust is primarily found in the HEAT.

If you think about it, if it takes 15 horsepower to cruise down teh road, then there is 15 horsepower going out the tail pipe, and 15 horsepower in the radiator.

If we could figure out a way to make a Rankine cycle even 20 percent efficient we could almost double our mileage!

[serialk11r]

Originally Posted by payne171

And at 400C, isn't exhaust manifold pressure going to be almost 65% over atmospheric pressure?

Nope, it depends on the exhaust system. If it's a restrictive exhaust, sure it could be that high under high power situations. You are right that a slightly more restrictive turbine could replace the muffler requirements, and that's a great idea, but in a well designed exhaust system there is very little backpressure. Think about a compressed air bottle, if you attach a pipe to the outlet and let the gas out, the gas is not going to be at the pressure in the air bottle. The pressure has turned into "kinetic energy", as the gas is now travelling at a higher velocity but with lower static pressure.

The pressure isn't constant. The "static pressure" shall we say, inside the pipe, is what the pistons have to push against. The reason the exhaust valves open early is so the gas blows itself down the exhaust pipe instead of using the piston's energy to do it.

drmiller100, no, a turbine does not convert heat energy. A turbine can only work across a pressure gradient. If you have a straight pipe with air blowing through and a flame, and you place a turbine downstream, it will do absolutely nothing. A turbine can use heat energy only when the heat is used to heat a gas in a closed chamber, which increases its pressure and allows the turbine to extract some of the energy.

[user removed]

Originally Posted by drmiller100

you guys are making it too complicated. a ROUGH general rule - 1/3 energy of the gasoline goes to work, 1/3 goes to radiator, and 1/3 goes out the exhaust as heat.

The exhaust side of turbochargers work primarily becuase of HEAT, not pressure. The ENERGY in the exhaust is primarily found in the HEAT.

If you think about it, if it takes 15 horsepower to cruise down teh road, then there is 15 horsepower going out the tail pipe, and 15 horsepower in the radiator.

If we could figure out a way to make a Rankine cycle even 20 percent efficient we could almost double our mileage!

The best way to increase engine efficiency, is to minimise it's operation as a function of time and maximise its efficiency in the time periods when it is running. That screams for capacitive storage of short bursts of operation when cruising at low overall loads.

Obviously this is why P&G can make a huge difference in overall consumption.
Once the strategy becomes a component of vehicle design, then you can add systems to minimise heat losses.

Make the vehicle capable of internal P&G operation and eliminate all the waste heat generation during the majority of time by simply eliminating the source of waste.

regards
Mech

[payne171]

Yes it is emptying pressure down the exhaust, but it has to spin the turbine to leave. Then more exhaust leaves the engine and adds more pressure. I think we are at an impasse. I would love to hear why it is more efficient to spin a supercharger with a turbine than the crankshaft, but not more efficient to turn a generator (switched reluctance, which is a key part of the process from what the article said) with the exhaust than with the crankshaft. I also would like to know why a team of engineers think it will work but you can sit down with a calculator and dismiss the possibility with a few calculations. There must be some lousy engineers in Great Britain. Either that, or they know something you don't. I wonder which one it is?

[drmiller100]

payne, i think using the exhaust for generating electricity is a GREAT idea.

1/3 of the gasolines energy goes out the exhaust as heat. if we can harness this, we can get "free" power!

[oil pan 4]

Originally Posted by payne171

I would love to hear why it is more efficient to spin a supercharger with a turbine than the crankshaft, but not more efficient to turn a generator (switched reluctance, which is a key part of the process from what the article said)

The difference between a super charger and a turbocharger is the super charger is a pump bolted on to the engine being driven by shaft power.
A turbocharger is a heat engine. A brayton cycle engine.
The brayton cycle is purely driven by waste heat from the diesel cycle.
A turbodiesel is a combinded cycle heat engine, more efficient than a diesel cycle with an extra pump attached.

Later I will tell why a turbine driven alternator would suck.

[serialk11r]

I never said it's not as efficient, I just said it's not as good as you make it out to be. I think in the last several posts I explained that yes it does improve efficiency. But it cannot utilize pure thermal energy. I'll let someone else try to explain, I think I've done the best I can.

I'll try to clarify one more thing. A turbocharger is barely more efficient than a supercharger. Both are deprovements over a naturally aspirated engine running full power, Otto cycle with blowby losses. The best thing about a turbocharger is that the design lends itself to very high specific power achievable.

[drmiller100]

Originally Posted by serialk11r

I never said it's not as efficient, I just said it's not as good as you make it out to be. I think in the last several posts I explained that yes it does improve efficiency. But it cannot utilize pure thermal energy. I'll let someone else try to explain, I think I've done the best I can.

I'll try to clarify one more thing. A turbocharger is barely more efficient than a supercharger. Both are deprovements over a naturally aspirated engine running full power, Otto cycle with blowby losses. The best thing about a turbocharger is that the design lends itself to very high specific power achievable.

I invite you to do the math on a Turbocharger.

On the engine side, 1200 degrees, 30 psi absolute. On the atmospheric side, 300 degrees, and 15 psi absolute.

Assume 2 liter engine, at 3000 rpm.

Calculate the horsepower available in the exhaust.

(Hint. Check your work by comparing to dyno chart of a 2 liter engine at 15 psi boost spinning at 3000 rpm).