Why are Mazda persisting with the Rotary Wankel engine?
Discussion
SuperchargedVR6 said:
But have they improved the torque outut? A turbo would help in that department I guess!
Nothing wrong with the torque output of them. The issue has always been comparing apples with oranges. For example comparing a 1.3l Rotary with a 3.5l v6...Compare them with similar and there is little if any difference.
Mave said:
The technology may be offering efficiency and emission improvements for a rotary engine used in each of those applications, BUT the chinning bar varies between those applications.
Having the technology to meet the (current?) efficiency levels of an automotive piston engine is NOT the same as meeting the efficiency levels of a marine piston or gas turbine engine. Even if you make a rotary engine perfect at performing its thermodynamic cycle (which is what this technology is trying to do), that thermodynamic cycle has a fundamental efficiency limit.
Marine is moving over to electric drive props with engines in a genset running at near to optimum performance as possible at a constant speed. Diesel/electric trains have been doing this for countless decades. Autos are moving that way as well with series-hybrids. Maybe you are thinking of large, slow revving, gigantic, direct drive, marine diesels. Having the technology to meet the (current?) efficiency levels of an automotive piston engine is NOT the same as meeting the efficiency levels of a marine piston or gas turbine engine. Even if you make a rotary engine perfect at performing its thermodynamic cycle (which is what this technology is trying to do), that thermodynamic cycle has a fundamental efficiency limit.
RayTay said:
Mave said:
The technology may be offering efficiency and emission improvements for a rotary engine used in each of those applications, BUT the chinning bar varies between those applications.
Having the technology to meet the (current?) efficiency levels of an automotive piston engine is NOT the same as meeting the efficiency levels of a marine piston or gas turbine engine. Even if you make a rotary engine perfect at performing its thermodynamic cycle (which is what this technology is trying to do), that thermodynamic cycle has a fundamental efficiency limit.
Marine is moving over to electric drive props with engines in a genset running at near to optimum performance as possible at a constant speed. Diesel/electric trains have been doing this for countless decades. Autos are moving that way as well with series-hybrids. Maybe you are thinking of large, slow revving, gigantic, direct drive, marine diesels. Having the technology to meet the (current?) efficiency levels of an automotive piston engine is NOT the same as meeting the efficiency levels of a marine piston or gas turbine engine. Even if you make a rotary engine perfect at performing its thermodynamic cycle (which is what this technology is trying to do), that thermodynamic cycle has a fundamental efficiency limit.
The implication of Mazda's quote is that they are working on technology to get to high 20s / low 30s efficiency at best. This may be viable for automotive, but not for marine. It doesn't matter whether you put lots of them together, have one big one, operate through a gearbox, through an alternator.... if the peak prime mover efficiency is in the 30s then its fundamentally not going to have better fuel consumption than a gas turbine operating at least mid 30s on a simple cycle, potentially up to low 50s with more complex cycle optimisation.
Mave said:
No, I'm not thinking of slow revving gigantic direct drive marine diesels; but either way that is irrelevant to the point.
The implication of Mazda's quote is that they are working on technology to get to high 20s / low 30s efficiency at best. This may be viable for automotive, but not for marine. It doesn't matter whether you put lots of them together, have one big one, operate through a gearbox, through an alternator.... if the peak prime mover efficiency is in the 30s then its fundamentally not going to have better fuel consumption than a gas turbine operating at least mid 30s on a simple cycle, potentially up to low 50s with more complex cycle optimisation.
What thermal efficiencies Mazda come up with is yet to be seen. However an engine optimised for genset applications tend to be more efficient in operation. A genset supplying electricity to move a ship or bus or truck cares not a jot what is being moved or what uses the produced electricity. Look at the marine engines in cruise liners. They are the same as used in static mounted genset electricity production. Decoupling the engine from driving motor makes matters very different. It is a great leveller. The implication of Mazda's quote is that they are working on technology to get to high 20s / low 30s efficiency at best. This may be viable for automotive, but not for marine. It doesn't matter whether you put lots of them together, have one big one, operate through a gearbox, through an alternator.... if the peak prime mover efficiency is in the 30s then its fundamentally not going to have better fuel consumption than a gas turbine operating at least mid 30s on a simple cycle, potentially up to low 50s with more complex cycle optimisation.
Steam turbines are still operating in power stations. Hopefully gas turbines have tipped over in the running costs. Then there will be widespread adoption.
RayTay said:
Mave said:
No, I'm not thinking of slow revving gigantic direct drive marine diesels; but either way that is irrelevant to the point.
The implication of Mazda's quote is that they are working on technology to get to high 20s / low 30s efficiency at best. This may be viable for automotive, but not for marine. It doesn't matter whether you put lots of them together, have one big one, operate through a gearbox, through an alternator.... if the peak prime mover efficiency is in the 30s then its fundamentally not going to have better fuel consumption than a gas turbine operating at least mid 30s on a simple cycle, potentially up to low 50s with more complex cycle optimisation.
What thermal efficiencies Mazda come up with is yet to be seen. However an engine optimised for genset applications tend to be more efficient in operation. A genset supplying electricity to move a ship or bus or truck cares not a jot what is being moved or what uses the produced electricity. Look at the marine engines in cruise liners. They are the same as used in static mounted genset electricity production. Decoupling the engine from driving motor makes matters very different. It is a great leveller. The implication of Mazda's quote is that they are working on technology to get to high 20s / low 30s efficiency at best. This may be viable for automotive, but not for marine. It doesn't matter whether you put lots of them together, have one big one, operate through a gearbox, through an alternator.... if the peak prime mover efficiency is in the 30s then its fundamentally not going to have better fuel consumption than a gas turbine operating at least mid 30s on a simple cycle, potentially up to low 50s with more complex cycle optimisation.
How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
Mave said:
So if you don't know what thermal efficiencies Mazda are expecting, how can you say that they will have better fuel consumption than gas turbines that have been demonstrated in actual, marine, genset operations to have greater efficiency than marine piston engines that themselves have greater efficiency than automotive piston engines that Mazda re trying to reach?
How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
I'd have thought turbo-charging or turbo-compounding, the rotary has a *lot* going for it in comparison to a piston engine WRT to FI. How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
Ignoring any developments Mazda have made recently a small turbo compound rotary could achieve a BSFC of about .36 to .40.
Fastdruid said:
Mave said:
So if you don't know what thermal efficiencies Mazda are expecting, how can you say that they will have better fuel consumption than gas turbines that have been demonstrated in actual, marine, genset operations to have greater efficiency than marine piston engines that themselves have greater efficiency than automotive piston engines that Mazda re trying to reach?
How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
I'd have thought turbo-charging or turbo-compounding, the rotary has a *lot* going for it in comparison to a piston engine WRT to FI. How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
Ignoring any developments Mazda have made recently a small turbo compound rotary could achieve a BSFC of about .36 to .40.
Mave said:
Fastdruid said:
Mave said:
So if you don't know what thermal efficiencies Mazda are expecting, how can you say that they will have better fuel consumption than gas turbines that have been demonstrated in actual, marine, genset operations to have greater efficiency than marine piston engines that themselves have greater efficiency than automotive piston engines that Mazda re trying to reach?
How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
I'd have thought turbo-charging or turbo-compounding, the rotary has a *lot* going for it in comparison to a piston engine WRT to FI. How are you going to combine and optimise rotary engines and hybrids and whatnot with a fundamental maximium 25% efficiency, to have better fuel consumption than an engine that already delivers 40%?
Ignoring any developments Mazda have made recently a small turbo compound rotary could achieve a BSFC of about .36 to .40.
Fastdruid said:
Ignoring any developments Mazda have made recently a small turbo compound rotary could achieve a BSFC of about .36 to .40.
Correct. And that is with the older rotary technology. It will be interesting to see what Mazda have come up with. They appear to have locked on to HCCI and may or may not fit a turbo. They ultimate aim is mass production of rotaries that drive everyday cars. That is not to say, they are not scalable up and down. It is interesting to see if the rotary or the gas turbine will win in the series-hybrid mode. Or maybe both will be there. Or maybe all electric will eclipse both. One thing is clear is the end of the piston engine is nearing. In 50 years time old diesel lumps may be curios like steam engines in trucks. Interesting times indeed.
hidetheelephants said:
Mave said:
Fastdruid said:
It doesn't have valves. For a piston engine the kinetic energy for recovery is about 6%, for a rotary it's about 16.5%.
What do you mean by "kinetic energy for recovery"?[/footnote]
Edited by Mave on Tuesday 9th August 23:16
Mave said:
What do you mean by "kinetic energy for recovery"?
I think Fastdruid means the rotary engine has far less engine brake in exhaust gas ejection. Engine brake saps produced power. Rotaries are noted for spinning, changing down gears never does much to slow a car. I will let him explain though. Edited by RayTay on Wednesday 10th August 10:02
RayTay said:
Steam turbines are still operating in power stations. Hopefully gas turbines have tipped over in the running costs. Then there will be widespread adoption.
I realise it's getting off topic somewhat, but it sounds like you think steam turbines are old hat?I would like to see what alternatives there are, to generate the level of power required at any of the major power stations, that don't use steam. And that come even close to a steam turbine in terms of overall efficiency.
That aside, without a steam turbine, a nuclear power station is pretty useless, unless there's something else you can do with all the heat generated.
RayTay said:
Mave said:
What do you mean by "kinetic energy for recovery"?
I think Fastdruid means the rotary engine has far less engine brake in exhaust gas ejection. Engine brake saps produced power. Rotaries are noted for spinning, changing down gears never does much to slow a car. I will let him explain though. Edited by RayTay on Wednesday 10th August 10:02
Fastdruid said:
It doesn't have valves. For a piston engine the kinetic energy for recovery is about 6%, for a rotary it's about 16.5%. So if you can get the economy for the "engine" bit *near* to a piston engine then you could then recover far more from the exhaust and (in theory at least) make it more economic (in BSFC terms anyway) than a piston engine.
from wiki:"A wankel rotary engine is still a four-stroke engine and pumping losses from non-power strokes still apply, but the absence of throttling valves and a 50% longer stroke duration result in a significantly lower pumping loss compared to a four-stroke reciprocating piston engine."
Mave said:
OK, what do you mean by "engine brake in exhaust gas ejection"? Especially in the context of steady state design point operation?
I 'think' Fastdruid means that there is less resistance in a rotary, as it has no exhaust valve, in ejecting the exhaust gasses from the engine. Lower pumping losses. There is more resistance forcing the exhaust gasses though of a small valve opening than a larger exhaust port. Having a valve with a small orifice means the piston/rotor works harder to eject the gasses which consumes power from the mainshaft. Super Slo Mo said:
I realise it's getting off topic somewhat, but it sounds like you think steam turbines are old hat?
I would like to see what alternatives there are, to generate the level of power required at any of the major power stations, that don't use steam. And that come even close to a steam turbine in terms of overall efficiency.
That aside, without a steam turbine, a nuclear power station is pretty useless, unless there's something else you can do with all the heat generated.
Super Slo Mo, I do not think steam turbines are old hat at all. They are very efficient at niche applications, ideal for power generation. Water turbines likewise. In the past decade or so there has been quite a bit of R&D in small steam engines. Using external continuous combustion is far cleaner in emissions than a series of dirty explosions. But everything is aiming for electric traction drive and steam seems to have been put on the back burner. It is what range-extender (genset) will win: rotary, gas turbine, free piston, Stirling or even steam. I would like to see what alternatives there are, to generate the level of power required at any of the major power stations, that don't use steam. And that come even close to a steam turbine in terms of overall efficiency.
That aside, without a steam turbine, a nuclear power station is pretty useless, unless there's something else you can do with all the heat generated.
RayTay said:
'think' Fastdruid means that there is less resistance in a rotary, as it has no exhaust valve, in ejecting the exhaust gasses from the engine. Lower pumping losses. There is more resistance forcing the exhaust gasses though of a small valve opening than a larger exhaust port. Having a valve with a small orifice means the piston/rotor works harder to eject the gasses which consumes power from the mainshaft.
Fair enough, but that thought process leads back to discussing gas turbines vs rotary. Compounding is really a band aid for sub-optimum expansion, caused by mechanical coupling of the compression and exhaust strokes of piston and rotary engines. If you're going to the trouble of introducing a high speed turbine into a compound engine, then why wouldn't you extend that philosophy to have a gas turbine core rather than a rotary core?Gassing Station | General Gassing | Top of Page | What's New | My Stuff