Atkinson cycle engines?

[jaylw314]

Random thought, but I'd never heard of Atkinson cycle engines until recently, and now it looks like they're coming out of the woodworks.  Is there any reason other than design inertia that we don't hear about them in aviation?

My understanding is that the original idea would have been too complicated, requiring additional shafts to make the intake and exhaust cycles different lengths.  It looks like most implementations in cars now simply have the intake valve open for part of the compression cycle to reduce the volume of the fuel/air mix, which seems like a mechanically simple technique.

Aside from slightly better efficiency, it seems like the main benefit in aircraft motors would be to reduce or obviate the risk of detonation, since the intake compression ratio would be significantly lower before combustion.  I've read that low-end power suffers in comparison, but that would not be much of an issue in aircraft.

Is this a thing anywhere in aircraft already?

[Fly Boomer]

9 minutes ago, jaylw314 said:

Random thought, but I'd never heard of Atkinson cycle engines until recently, and now it looks like they're coming out of the woodworks.  Is there any reason other than design inertia that we don't hear about them in aviation?

My understanding is that the original idea would have been too complicated, requiring additional shafts to make the intake and exhaust cycles different lengths.  It looks like most implementations in cars now simply have the intake valve open for part of the compression cycle to reduce the volume of the fuel/air mix, which seems like a mechanically simple technique.

Aside from slightly better efficiency, it seems like the main benefit in aircraft motors would be to reduce or obviate the risk of detonation, since the intake compression ratio would be significantly lower before combustion.  I've read that low-end power suffers in comparison, but that would not be much of an issue in aircraft.

Is this a thing anywhere in aircraft already?

Less power than Otto.  To get the power back up, you would need a larger, heavier engine.

[jaylw314]

Just now, Fly Boomer said:

Less power than Otto.  To get the power back up, you would need a larger, heavier engine.

Turbochargers could make up for that, though, right? 

[dzeleski]

18 minutes ago, jaylw314 said:

Random thought, but I'd never heard of Atkinson cycle engines until recently, and now it looks like they're coming out of the woodworks.  Is there any reason other than design inertia that we don't hear about them in aviation?

My understanding is that the original idea would have been too complicated, requiring additional shafts to make the intake and exhaust cycles different lengths.  It looks like most implementations in cars now simply have the intake valve open for part of the compression cycle to reduce the volume of the fuel/air mix, which seems like a mechanically simple technique.

Aside from slightly better efficiency, it seems like the main benefit in aircraft motors would be to reduce or obviate the risk of detonation, since the intake compression ratio would be significantly lower before combustion.  I've read that low-end power suffers in comparison, but that would not be much of an issue in aircraft.

Is this a thing anywhere in aircraft already?

Atkinson cycle engines are really only beneficial at lower loads. This is why hybrids typically have a true Atkinson cycle engine, but even those engines are no longer really Atkinson engines anymore. Modern engines are mostly Otto with a mock Atkinson variable cam timing that puts them into a similar state. Any of those engines immediately move into Otto mode the second you request any power.

The reason this doesnt really work for most piston airplanes is because we are operating at much higher loads then a car is at 60mph down the highway. We regularly operate at 65-100% of available power. Your car probably uses 10-20% of its peak power cruising down the highway.

[dzeleski]

8 minutes ago, jaylw314 said:

Turbochargers could make up for that, though, right? 

Cant really use a turbo on a atkinson cycle engine. You wouldnt allow that air to go back into the manifold as the pressure would prevent it from happening. Thats why engine companies are moving to VVT to change how the engine works based on load.

[N201MKTurbo]

If you got a bunch of investors together and and got a few hundred million dollars together, put together a development team, building, flight test aircraft, admin staff and all the other things necessary for an upstart company, you could probably get an engine to market in 10 years or so. If the company was actually able to sell these engines, the investors would get the bulk of the profits.

[jaylw314]

5 minutes ago, dzeleski said:

Cant really use a turbo on a atkinson cycle engine. You wouldnt allow that air to go back into the manifold as the pressure would prevent it from happening. Thats why engine companies are moving to VVT to change how the engine works based on load.

Apparently you can, but then it's called a Miller cycle engine? Never heard that term before

Obviously, VVT Is a no-go in aircraft engines, I was thinking just about mechanically simple ideas

[N201MKTurbo]

VVT would be a waste of time in an aircraft engine. We operate at a fixed power setting. The valve timing is already optimized for cruise power.

Like most of the modern control systems on automotive engines, they have very little value on an aircraft engine. 

Electronic fuel injection, electronic ignition, variable valve timing are all there to make the engine perform optimally at different speeds and loads. With aircraft, all anybody cares about is cruise performance. The engine is already optimized for that. I have never heard an aircraft owner complain that they use too much fuel while on final approach.

[dzeleski]

5 minutes ago, N201MKTurbo said:

VVT would be a waste of time in an aircraft engine. We operate at a fixed power setting. The valve timing is already optimized for cruise power.

Like most of the modern control systems on automotive engines, they have very little value on an aircraft engine. 

Electronic fuel injection, electronic ignition, variable valve timing are all there to make the engine perform optimally at different speeds and loads. With aircraft, all anybody cares about is cruise performance. The engine is already optimized for that. I have never heard an aircraft owner complain that they use too much fuel while on final approach.

Precisely. Once leaded fuel goes away I would love to see someone slap on EFI, O2 sensors and modern spark plugs and see how much power can get pulled out, I think there is a decent amount left on the table using modern systems. Even if peak power at sea level isnt increased, consistent and reliable power at any condition will be easier since the pilot wouldnt need to deal with it and accidentally put the red knob in an non optimal position.

[N201MKTurbo]

6 minutes ago, dzeleski said:

Precisely. Once leaded fuel goes away I would love to see someone slap on EFI, O2 sensors and modern spark plugs and see how much power can get pulled out, I think there is a decent amount left on the table using modern systems. Even if peak power at sea level isnt increased, consistent and reliable power at any condition will be easier since the pilot wouldnt need to deal with it and accidentally put the red knob in an non optimal position.

Sure, you could make it automatic, but you can't make it any better than you can make it now. 

So let's say you could make it 5% more powerful. That would get you 3 or 4 KTS more cruise speed, BFD.

[1980Mooney]

4 minutes ago, N201MKTurbo said:

Sure, you could make it automatic, but you can't make it any better than you can make it now. 

Right. Those things make the engine more efficient at the low power settings that automobiles typically operate. At wide open throttle peak power, you can’t make the physics any better. 

Edited June 20, 2023 by 1980Mooney

[1980Mooney]

1 hour ago, jaylw314 said:

Random thought, but I'd never heard of Atkinson cycle engines until recently, and now it looks like they're coming out of the woodworks.  Is there any reason other than design inertia that we don't hear about them in aviation?

My understanding is that the original idea would have been too complicated, requiring additional shafts to make the intake and exhaust cycles different lengths.  It looks like most implementations in cars now simply have the intake valve open for part of the compression cycle to reduce the volume of the fuel/air mix, which seems like a mechanically simple technique.

Aside from slightly better efficiency, it seems like the main benefit in aircraft motors would be to reduce or obviate the risk of detonation, since the intake compression ratio would be significantly lower before combustion.  I've read that low-end power suffers in comparison, but that would not be much of an issue in aircraft.

Is this a thing anywhere in aircraft already?

Why not KISS?  Keep It Simple Stupid. 
Just go with a 2 stroke diesel. DeltaHawk. Highest thermal efficiency you can get. 

[dzeleski]

18 minutes ago, N201MKTurbo said:

Sure, you could make it automatic, but you can't make it any better than you can make it now. 

So let's say you could could make it 5% more powerful. That would get you 3 or 4 KTS more cruise speed, BFD.

I think you are under selling not having to worry about leaning for DA or leaning on the ground. EFI is way more precise then our mechanical fuel injection, as well as the atomization being way better. A stronger more precise spark can provide a lot more power and better endurance. Timing could probably be pushed a little more as well. All of these things would also allow the engines compression to go up which would net more power on top of that.

Will the industry ever invest the money into it? No idea.

edit: https://www.flyefii.com/products/efii-systems/

I never trust the marketing wank, but it makes general sense as someone who has quite a bit of EFI tuning experience from racing.

[1980Mooney]

3 minutes ago, dzeleski said:

I think you are under selling not having to worry about leaning for DA or leaning on the ground. EFI is way more precise then our mechanical fuel injection, as well as the atomization being way better. A stronger more precise spark can provide a lot more power and better endurance. Timing could probably be pushed a little more as well. All of these things would also allow the engines compression to go up which would net more power on top of that.

Will the industry ever invest the money into it? No idea.

A stronger spark does not necessarily create more power. Power is a function of the thermodynamics of the hydrogen oxygen combustion. Only if there is a problem with ignition or flame propagation will a stronger spark help. 

[1980Mooney]

8 minutes ago, dzeleski said:

I think you are under selling not having to worry about leaning for DA or leaning on the ground. EFI is way more precise then our mechanical fuel injection, as well as the atomization being way better. A stronger more precise spark can provide a lot more power and better endurance. Timing could probably be pushed a little more as well. All of these things would also allow the engines compression to go up which would net more power on top of that.

Will the industry ever invest the money into it? No idea.

I think the DeltaHawk 2 stroke diesel is single lever. 
 

Diesel has the highest compression. 

Edited June 20, 2023 by 1980Mooney

[N201MKTurbo]

15 minutes ago, 1980Mooney said:

Why not KISS?  Keep It Simple Stupid. 
Just go with a 2 stroke diesel. DeltaHawk. Highest thermal efficiency you can get. 

Too bad it costs more than I paid for the whole plane. That would buy a lot of that old fashioned AVGAS.

The Delta Hawk doesn't make more power, it just gives you more range and saves you a few bucks.

If we could get the US oil production where it was before COVID, it would save more than a Delta Hawk. 

[N201MKTurbo]

It baffles me that everybody buys a Mooney for its fantastic performance and efficiency. Then as soon as they get it they start complaining about its poor performance and efficiency. 

[dzeleski]

11 minutes ago, 1980Mooney said:

A stronger spark does not necessarily create more power. Power is a function of the thermodynamics of the hydrogen oxygen combustion. Only if there is a problem with ignition or flame propagation will a stronger spark help. 

Of course, but a good solid spark provides the best case for consistent flame front propagation. If you want to squeak out every HP everything needs to be optimal. Small optimizations add up to a larger number. Better spark and better fueling means we could push the engine design in a slightly more aggressive manner since there is less pilot error. Our engines are 100% not optimally burning fuel on any regular basis.

[jaylw314]

I was wondering more so if the Atkinson would improve detonation margins at full power than efficiency, since we're having issues with 100LL.  It sounds like without turbo, no, since the motor would have to be larger.  With turbocharging?  The wikipedia entry for Miller cycle engines mentions it might, especially if the intake charge is intercooled. That would be interesting in that it is simply a different valve timing, we have turbos and intercoolers otherwise.  I realize, though that the risk/benefit ratio is unlikely to be there for R&D regardless.  This was strictly in the territory of 'thoughts while on the toilet'  

Edited June 20, 2023 by jaylw314

[EricJ]

46 minutes ago, dzeleski said:

I think you are under selling not having to worry about leaning for DA or leaning on the ground. EFI is way more precise then our mechanical fuel injection, as well as the atomization being way better. A stronger more precise spark can provide a lot more power and better endurance. Timing could probably be pushed a little more as well. All of these things would also allow the engines compression to go up which would net more power on top of that.

Will the industry ever invest the money into it? No idea.

Lycoming has been shipping theirs for some time.   There are production aircraft that use them.   I haven't heard much about the field experience with them yet.

https://www.lycoming.com/engines/ie2

46 minutes ago, dzeleski said:

edit: https://www.flyefii.com/products/efii-systems/

I never trust the marketing wank, but it makes general sense as someone who has quite a bit of EFI tuning experience from racing.

A couple of locals had these systems installed on RVs.   They liked them a lot.   They're interesting systems, for sure.

I've been around tuning for racing for a long time as well.   It's amazing what tradeoffs and optimizations can be done with the right tools, and it's disappointing that we get so little of that in general aviation.

[N201MKTurbo]

I just looked at what the experimental guys are doing for more HP. The most gain seems to be from the old fashioned race car stuff. High compression pistons, porting, polishing and 3 face valve jobs. The gains they are claiming from FI and EI seem kind of small. I think you can get away with polishing your certified engine and probably the three face valve job.

[1980Mooney]

10 hours ago, EricJ said:

Lycoming has been shipping theirs for some time.   There are production aircraft that use them.   I haven't heard much about the field experience with them yet.

https://www.lycoming.com/engines/ie2

A couple of locals had these systems installed on RVs.   They liked them a lot.   They're interesting systems, for sure.

I've been around tuning for racing for a long time as well.   It's amazing what tradeoffs and optimizations can be done with the right tools, and it's disappointing that we get so little of that in general aviation.

The only production aircraft that uses them is the Tecnam P2012.   They put some on the Lancair Evolution but I heard most owners removed them and converted to turboprop.  If you look at the specs the TEO540C1A used on the Tecnam (single turbo and no intercooler) is quite a bit heavier than the TIO-540.

The TEO540C1A is rated at 375 HP

The standard TIO-540-AE2A is rated at 350 HP.  It is much lighter and costs a lot less.

Aviation is a series of trade offs and optimizations.

[Fly Boomer]

15 hours ago, jaylw314 said:

Turbochargers could make up for that, though, right? 

That might work.

[A64Pilot]

On 6/20/2023 at 5:37 PM, N201MKTurbo said:

I just looked at what the experimental guys are doing for more HP. The most gain seems to be from the old fashioned race car stuff. High compression pistons, porting, polishing and 3 face valve jobs. The gains they are claiming from FI and EI seem kind of small. I think you can get away with polishing your certified engine and probably the three face valve job.

You can, the guy who built my motor does a 5 angle valve job and ports and polishes, they get away with porting and polishing by saying they are matching the ports, Idea being after clean up you make them the same size as the largest, but I strongly suspicion there is some shaping too.

He used to be a NASCAR engine builder, I think for Bill Elliot maybe? But maybe not because that’s hearsay.

‘I’ve heard that and other things he does gets up to a 10% increase in HP on a Dyno, I find that hard to believe, what I do believe is that an average fresh angle valve IO-360 may get 210 HP and a Gann Performance my get 10 over that.

Edited June 23, 2023 by A64Pilot

[A64Pilot]

What we are talking about increasing is the BSFC, and if you look it up an aircraft BSFC is actually not bad, considering it’s handicapped by air cooling and primitive ignition  and fuel systems. There are improvements, but water cooling for example adds a lot of weight and lots of complication, it’s been done, but I don’t think it worked as well as hoped. Wasn’t there a “liquid rocket”? Maybe I don’t remember well.

There are no true Atkinson cycle engines in Automobiles, the Toyota Prius was the first to emulate one with variable valve timing, even the emulation develops very little torque, but that’s OK because the Prius wasn’t meant to be a performance car, and it’s two electric motors make gobs of torque to cover for the little ICE motor on acceleration.

Atkinson cycle predates practicable  automobiles, it was late 1800’s 1880’s I think and the first Benz was about the same time, but the Model-T wasn’t until 1908?

On edit, Our detonation issue is more I believe a function of our primitive hemispherical combustion chamber.

More modern engines like the GM LS-7 have a pent roof combustion chamber and run 11 to 1 compression on car gas of course, but Pent roof requires four valves, and four valves require liquid cooling, that’s why in 1984 Kawasaki went to liquid cooled motors, so they could run a four valve head.

Edited June 23, 2023 by A64Pilot