Active Fuel Management / Cylinder Shutdown: GA Potential???

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cblink.007

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So, after an 11-month wait, the Mrs and I recently took delivery of a new GM sports car. Of all the things about this car, I’d have to say that the one thing that fascinates me the most is the LT2 plant that sits right behind me. In particular, I am extremely fascinated with the fuel economy this car gets when driving in the Tour mode. Back on Saturday, we took the car out for a 50-mile drive around the countryside.

We averaged 37.2 miles per gallon with an average speed around the route being 48.7 mph, including a couple stop lights & signs. Remarkable for a 6.2 liter V-8 that’s been officially rated at 495 bhp! Even in and around town, I average more than 25mpg, far better than the 315 bhp 3.0 turbo I-6 that powered the 2013 BMW 335is I used to have.

I knew that the powertrain did this by way of “Active Fuel Management”, also known as literally shutting down half the cylinders, among many things. What amazed me is how the car’s engine control module (we’ll just call it what it is…a FADEC) did this. Out of the maintenance manual, it discusses the theory of operation. Operationally, I still had considerable power margin at cruise speed with just 4 cylinders active, as I only used the cruise control for those portions that had steady state speeds. If I was driving in a 4-cylinder mode, if I let off the throttle or heavily applied it, it immediately switched back to a V-8 mode. It does appear that the FADEC also works in concert with the gearbox do deliver a steady state power output at speed; it also works with the valved exhaust system.

Long story short, this LT2 is a remarkable piece of powerplant engineering, and is probably the zenith of the Chevrolet pushrod small-block V-8 that first saw mass production back in the 1950s.

It makes me wonder. What is stopping groups like Continental from designing a piston aircraft engine that can operate like this? I am assuming money…and the massive a$$pain of certification. I kind of don’t think environmentals could factor into the reason as to why they don’t do this.

Granted, I heavily doubt that a current IO-320 or 540 could possibly be modified to operate like this. An entirely clean-sheet design would likely be necessary. I could envision such an engine that could operate on partial cylinders during taxiing and other low speed ground operations, all cylinders on demand, such as during takeoff and approach, and partial cylinders during the cruise phase. If achieving that kind of efficiency could be done without becoming excessively expensive or heavy without compromising reliability, performance, why not?

Again, I am not a piston engine SME, so this is all purely conjecture at this point, but let’s say you all!
LT2 AFM-1.jpg LT2 AFM-2.jpg
 

Victor Bravo

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I'm guessing that the weight penalty of carrying around four cylinders that are not being used for 90% of the flight is the one big deal-breaker in aviation that the automobiles can better deal with, due to the higher L/D of the car and the far lower penalty for excess weight???.
 

TFF

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The technology is great, when everything is new. There is a whole industry of defeat modification out there. Long term those can be the cylinders that oil up. It is a problem in high mileage cars. What they need is a system that can shut down any cylinder to keep it all even.

A flying buddy had one of the first versions of your new toy and it was the easiest car to drive, I have ever driven. Then bang for buck for serious performance is crazy. Seriously money, but not Ferrari serious for the same general performance.
 

gtae07

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Seems like solving the vibration/torsional resonance problem would be even more of a PITA. Plus, how much can you afford to deactivate with the aircraft needing 65-75% rated power in cruise? Then you'll need a FADEC, which isn't inherently bad but is a terribly expensive proposition for the certified market for multiple reasons.

The VCM on Honda Odysseys got a bad rep for killing piston rings and engine mounts, among other things. There are products available that you plug into a sensor harness that disable that "feature". I use one because I don't want to have to pay for an engine rebuild in the future.
 

cblink.007

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I'm guessing that the weight penalty of carrying around four cylinders that are not being used for 90% of the flight is the one big deal-breaker in aviation that the automobiles can better deal with, due to the higher L/D of the car and the far lower penalty for excess weight???.
That is almost the same as saying that you are flying with an engine capable of flying with 300 horsepower, but only requiring 175 of that to cruise; are you also carrying that dead weight as well? It is all relative, especially given that the mission profile of an aircraft would require full power availability if needed, even during the landing phase (go-around or missed approach).

As an example, when I operate the V-22 in VTOL mode for takeoff and landing, I am using up the better part of the 12,300 shaft horsepower I have at my disposal to get that beast airborne...all 50,000-plus pounds of it. However, when I convert to Airplane mode, where the engines throttle back to less than half of that rated output (with the proprotor speed dropping down to 84%), with the corresponding significantly lower fuel burn, one can easily say that we are carrying all the 'dead weight' of the nacelles. Hence this particular correlation to the LT2 AFM function.

adillac did this with their V8-6-4 way back when. I agree with TFF, alternating the cylinders that get shut off is the solution.
This I agree with. I do not understand why the LT2 only powers down certain cylinders without alternating them. I wish I had contacts at GM Powertrain Engineering to help explain this.

I do, however, have some contacts within the engineering group at Lycoming.... I have to ask them if they've toyed with this idea...unless GM has total IP control over this...
 

cblink.007

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Seems like solving the vibration/torsional resonance problem would be even more of a PITA. Plus, how much can you afford to deactivate with the aircraft needing 65-75% rated power in cruise? Then you'll need a FADEC, which isn't inherently bad but is a terribly expensive proposition for the certified market for multiple reasons.

The VCM on Honda Odysseys got a bad rep for killing piston rings and engine mounts, among other things. There are products available that you plug into a sensor harness that disable that "feature". I use one because I don't want to have to pay for an engine rebuild in the future.
True...all the more reason why such an engine would have to be designed...not modified from an existing. I know that the Cadillac XT4 that the Mrs has only has a 2.0L turbo 4-banger (the block & head actually appears to be nearly identical to the Suzuki G15bb that comprises the core of the @aeromomentum AM-15)...but it's "active fuel management" is simply stopping when the vehicle is temporarily stopped. The AFM that the LT2 does obviously works for a V-8 on the road, but yes, I do not think it would work all that well on a horizontally opposed 4-cyclinder...just on the basis of the fact that the engine would probably have to work even harder just to maintain 65% power demand...with all the TV issues going along with it.

Low power demand is also a requirement for the LT2's AFM modes to kick in. I might just have to do a 65 mph drive up a steady hill test, which would be a higher constant power demand, and see what happens.... in controlled conditions, of course 🤣

I've flown an O-320 that dropped a cylinder in flight....those elastomeric mounts got a good workout!
 

Dan Thomas

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Like gtae07 says, why? Airplanes are not cars. Their power needs are much higher. Dumping half the cylinders costs more than half the power, as the dead pistons are still being pushed around, and who cruises at 50%? That power level is approaching max endurance (best time aloft for fuel available) but you're at best L/D, a slow speed, going nowhere.
 

TFF

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Why do Rolls Royce deprecate so much? Because the first buyer is who counts. GM doing it the way they did it is just a cost cutting, because 99% of buyers will be sellers. It still works as intended job for a long time. Once the warranty is done, they have no interest. As an enthusiast, it is frustrating. I buy third hand. The modern cars either never reach this point, or they are uneconomical to try and fix.

While the modern automatic will be a faster car, the person who comes up with a mechanical shifter retro and a clutch pedal will rule the sports car enthusiast world.
 

llemon

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Aircraft piston engines are more or less designed to run at 75% with some compromises to allow for a higher takeoff power. That takeoff power will be around a BSFC of 0.55-0.6, which is quite a bit worse than the 0.4-0.45 BSFC in cruise. But that additional ~0.1-0.15lb per hp hardly matters when that peak power is only used for >5% of the flight.

Car engines have a far wider operating range and benefit from complicated things that widen that envelope, ie shutting off cylinders, VVT, sequential turbos, ect.
 

wsimpso1

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Cars spend a huge amount of the drive cycle below 50% torque and below 25% power, so they can run with cylinder deactivation. The other thing that lets car/truck engines do this is that they are water cooled, so all the cylinders can be kept warm while running in cylinder deactivation.

in detail, fuel is shut off AND valves are not opening, then the remaining cylinders run at a large percentage of possible airflow and right on stoich. With automatic tranny and engine controlled together, the drive tells the car how fast to go or how much of its acceleration is desired, and the engine and gear state are picked to deliver that torque at min fuel burn.

The other scheme for efficiently powering our road vehicles is to run an engine that in steady state is running manifold pressures of 15-22 in Hg, then boost to 60 In Hg or more when power is demanded. Combined with good auto tranny schemes, this too gives fabulous fuel economy and good performance.

Most Of us run our airplanes at 100% power for takeoff, 90-75%power for climb, and then 50-75% power in cruise. With an engine oversized, for cruise and water cooled, cylinder deactivation could work. Imagine a water cooled IO-540 in and airplane that gives adequate climb and cruise with an IO-360. Shut off two out of six in cruise and you still have terrific takeoff and climb performance. You still add 100+ pounds. Plus all the hardware to deactivate valves and electronic fuel injection to shut off fuel.

Last scheme would be to build engines with good durability when run at 45-60 In Hg, and then reduce to 30 In Hg for cruise.

Both schemes will require new engines and controllable props.

Just to put a scale on this, a new engine or a new transmission out of the automakers is about a Billion dollars between design effort, prototypes, development, testing, and getting the factory tooled up. Sure, with smaller volumes, the factory cost and prototype volumes will be a lot smaller, but will still take a pile of money for a little volume… I would not invest in that scheme with my money, and I would be skeptical of taking employment with some doing it…

Billski
 

Bill-Higdon

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Cars spend a huge amount of the drive cycle below 50% torque and below 25% power, so they can run with cylinder deactivation. The other thing that lets car/truck engines do this is that they are water cooled, so all the cylinders can be kept warm while running in cylinder deactivation.

in detail, fuel is shut off AND valves are not opening, then the remaining cylinders run at a large percentage of possible airflow and right on stoich. With automatic tranny and engine controlled together, the drive tells the car how fast to go or how much of its acceleration is desired, and the engine and gear state are picked to deliver that torque at min fuel burn.

The other scheme for efficiently powering our road vehicles is to run an engine that in steady state is running manifold pressures of 15-22 in Hg, then boost to 60 In Hg or more when power is demanded. Combined with good auto tranny schemes, this too gives fabulous fuel economy and good performance.

Most Of us run our airplanes at 100% power for takeoff, 90-75%power for climb, and then 50-75% power in cruise. With an engine oversized, for cruise and water cooled, cylinder deactivation could work. Imagine a water cooled IO-540 in and airplane that gives adequate climb and cruise with an IO-360. Shut off two out of six in cruise and you still have terrific takeoff and climb performance. You still add 100+ pounds. Plus all the hardware to deactivate valves and electronic fuel injection to shut off fuel.

Last scheme would be to build engines with good durability when run at 45-60 In Hg, and then reduce to 30 In Hg for cruise.

Both schemes will require new engines and controllable props.

Just to put a scale on this, a new engine or a new transmission out of the automakers is about a Billion dollars between design effort, prototypes, development, testing, and getting the factory tooled up. Sure, with smaller volumes, the factory cost and prototype volumes will be a lot smaller, but will still take a pile of money for a little volume… I would not invest in that scheme with my money, and I would be skeptical of taking employment with some doing it…

Billski
I've heard from some people these engines wear out faster that an engine that runs all cylinders all the time
 

wsimpso1

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The engines with cylinder deactivation pass the same long term durability tests as the engines they are based on. Cylinder deactivation is achieved by valve deactivation. The valves stay closed, the air trapped above the piston is expanded and compressed and expanded and compressed in a near reversible set of processes that bleeds down to near ambient pressure at mid stroke. The thermostat keeps the coolant at about the same temp continuously, so the cylinders and heads only run slightly cool. In general, there is not much going on with the deactivated cylinders that would not be going on with the engine running 30% of max torque anyway.

The cylinders that are running at 80% of max torque are running at a little higher temps than atvsay 40% torque but the LS engines are WAY robust.

At Ford, we found we could get a fuel economy bonus with cylinder deactivation in cars. In trucks and SUV, it was a wash. At Chrysler/FCA, we were doing it in trucks and SUV knowing that fuel economy benefit was tiny but knowing that in a city cycle it could benefit the customer. At FCA in big engine cars it is a benefit.

Most of where the auto industry has gone is small turbocharged engines to allow low fuel burn most of the time, and then boost for when the customer pushes down on the gas. Lesson for us in airplanes with auto engines and good turbocharging.

Billski
 

cblink.007

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Okay fam, so yesterday on the drive home, I took a different route for a road that had a more constant gradient. I opened it up to what I think was about 25% demand. Cylinder shutdown did not occur at all over three attempts, despite the relatively consistent load. However, letting it off some, to about 10% or so, it would cycle into V4 mode, it operated as described in the manual's theory of operation. I could get into the LT2's differing behavior during the newly unlocked Sport, Track, Weather and Z Modes (as it now allows me to select it, having recently passed the 500 mile mark), but that is for another forum

I did, however, talk with a Lycoming colleague last night about this. When cylinder deactivation hit the road some 20-plus years ago, the company did in fact toy with the idea, going as far as getting a heavily modified IO-540 onto a test cell for evaluation. They determined it not to be practical for a number of reasons, primarily due to the facts that doing something like this with an air cooled will open the door to cylinder damage (if the plant was liquid cooled, this would not be much of an issue, hence the reason why it works in some auto applications), but more importantly, excessive torsional vibrations occurred, but was a direct consequence of the mule plant design (as it was literally operating with a dropped cylinder). He did say though that something like this could work with a bespoke designed 8-cylinder aircraft plant, but he thinks the best route forward for our particular aircraft group is either small displacement with turbocharging and or hybrid electric...which he did [not] say on the record is under development at [not] Lycoming.
 

Tom DM

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So, after an 11-month wait, the Mrs and I recently took delivery of a new GM sports car. Of all the things about this car, I’d have to say that the one thing that fascinates me the most is the LT2 plant that sits right behind me. In particular, I am extremely fascinated with the fuel economy this car gets when driving in the Tour mode. Back on Saturday, we took the car out for a 50-mile drive around the countryside.

We averaged 37.2 miles per gallon with an average speed around the route being 48.7 mph, including a couple stop lights & signs. Remarkable for a 6.2 liter V-8 that’s been officially rated at 495 bhp! Even in and around town, I average more than 25mpg, far better than the 315 bhp 3.0 turbo I-6 that powered the 2013 BMW 335is I used to have.


I hate to spoil but know that the splendid new GM sports car is designed to be scrap in about 10 years and possible quite a bit sooner if a minor mishap were encountered. Actual cars are not build to last nor to be repaired: they are to be replaced preferentially the moment you drive of the dealers lot. The last thing they are allowed for, is to extract their nominal potential.

The 495 HP engine produces 48.7 mpg because it is driven at less 15% of its nominal power.

From our race engines I know exactly how long they last under racing conditions: for shorter races about 20 hours, in endurance trim: about 50 hours.
That is almost the same as saying that you are flying with an engine capable of flying with 300 horsepower, but only requiring 175 of that to cruise; are you also carrying that dead weight as well? It is all relative, especially given that the mission profile of an aircraft would require full power availability if needed, even during the landing phase (go-around or missed approach).

As an example, when I operate the V-22 in VTOL mode for takeoff and landing, I am using up the better part of the 12,300 shaft horsepower I have at my disposal to get that beast airborne...all 50,000-plus pounds of it. However, when I convert to Airplane mode, where the engines throttle back to less than half of that rated output (with the proprotor speed dropping down to 84%), with the corresponding significantly lower fuel burn, one can easily say that we are carrying all the 'dead weight' of the nacelles. Hence this particular correlation to the LT2 AFM function.


This I agree with. I do not understand why the LT2 only powers down certain cylinders without alternating them. I wish I had contacts at GM Powertrain Engineering to help explain this.

I do, however, have some contacts within the engineering group at Lycoming.... I have to ask them if they've toyed with this idea...unless GM has total IP control over this...


There are a few minor differences in the concept of the engines of the V-22 and the "new" GM Sportscar.

The V22 is designed for certain operational life, requires per flight hour about 15000 US$ of maintenance. Its 12300 Horses are there as they are needed and *will* be used.

The GM car is designed for a life span of about 10 years with nil maintenance (and within 10 years close to nobody at the GM dealership will have the knowledge to work on them). The GM-car is a consumer good and it will close to never be used at its nominal power ( about 0.1% of its total life span).

At full chat the 495 GM horses drink the tank in about 30 minutes (flow rate 150 l / hr). Highly doubtfull that even a V-22 pilot who performs that on the road will be alive after those 30 minutes (let alone the car).

As luck has it , an (old) new car also wormed its way in my garage, number 15 has a power to weight ratio of 400 HP/ ton. It can't be more opposite to yours: this 1985 vintage will be with me for the next 25 years (unless I wrap it round a tree). This "newcomer" is not a consumption item but with its flashy yellow color it might eat drivers licenses alarmingly.

Happy for you and happy for me: no ABS to break, no roof, no windshield, (also no wipers), no traction control but my right foot, 6 speed sequential, no windows, no doors. I expect 100% reliability of the parts not there (quite less for those that are there).

We'll surely meet at some red light, make noise and be photographed by a few lovely girls! The older (more wiser) will point their index finger towards forehead while make circular mouvements with that hand ;)
 
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