Advantages of sleeve valves for H-24 engines?

[z42]

re Heat conduction of sleeves

Ricardo stated:

(2) That a moving sleeve, provided that only a thin oil film was maintained, appeared to be almost transparent to heat.
"The High-Speed Internal-Combustion Engine", Ricardo, Fourth Edition, 1954 Reprint, p349. [Ricardo made significant changes between editions.]

Fedden's paper "The Development of the Mono-Sleeve Valve for Aero Engines" Feb, 1939 stated in response to a question:
"I must again emphasize Mr. Ricardo's remarks about the transparency of the sleeve and the rubbing motion of the oil film, which is the real crux of that problem."

I had to do a heat transfer calculation on a 1/2" pipe at 1300°F, and was surprised to see that the temperature difference across the carbon steel pipe was 0.84 K. I changed the conduction coefficient to that of KE965 and the thickness to 1/8" and ran calcs from 2500°F to 500°F. I found that the temperature difference across the sleeve varied from 8 K at 2500°F to 0.5 K at 500°F. For me there seems no reason to doubt Ricardo's claim, with the same caveat - the oil film must be maintained.

There are certainly many metal alloys with very good heat conductivity. I suspect we shouldn't discount the effect of the oil film, particularly if there are voids (bubbles) in the film, that could cause the heat conductivity to drop dramatically. If the interface between the cylinder wall and the sleeve insulate the sleeve, it doesn't help that much if the sleeve itself has good heat conductivity.

The enginehistory.org site has a paper about sleeve valves referring to two articles by Fedden [1] and Hives [2] claiming a measured 50C difference in piston temps vs a comparable poppet valve engine. If this is representative of sleeve valve engines in general, that's quite a huge difference.

[1] Fedden, A.H.R., "Aircraft Power Plants – Past and Future," Journal of the Royal Aeronautic Society, Vol. 48, pp. 397-459, October 1944.
[2] Hives, E.W. and Smith, F.L., "High Output Aircraft Engines," SAE Journal, Vol. 46, No. 3, pp. 106-117, March 1940.

 

[Reluctant Poster]

Close but no cigar:

If sleeve is just moving up and down, there are 3 issues:
1. You are stopping and start the motion of the sleeve similar to what is happening with the piston. So, you need a similar crank and rods - the sleeve crank only needs to be running 1/2 of the main crank but they are still going to be substantial items.
2. You need sleeve inside of a sleeve (dual sleeves) if you want to be able to properly control the timing of the intake and exhaust cycles. If you thought it was challenging with piston inside of sleeve inside the block, add another sleeve. The inner sleeve needs to extend past the outer sleeve which makes it longer = heavier.
3. And to paraphrase D Deleted member 68059 from the Sleeve Valves at high rpms thread, the multiple oil films over the large surface area of the all the sleeves adds internal friction.

The rotating motion of the Bristol and Napier drives was both smoother and allowed ports to be "timed".

The Knight engine used two sleeves and was quite successful as far as sleeve valve engines go.

 

[Simon Thomas]

There are certainly many metal alloys with very good heat conductivity. I suspect we shouldn't discount the effect of the oil film, particularly if there are voids (bubbles) in the film, that could cause the heat conductivity to drop dramatically. If the interface between the cylinder wall and the sleeve insulate the sleeve, it doesn't help that much if the sleeve itself has good heat conductivity.

The enginehistory.org site has a paper about sleeve valves referring to two articles by Fedden [1] and Hives [2] claiming a measured 50C difference in piston temps vs a comparable poppet valve engine. If this is representative of sleeve valve engines in general, that's quite a huge difference.

[1] Fedden, A.H.R., "Aircraft Power Plants – Past and Future," Journal of the Royal Aeronautic Society, Vol. 48, pp. 397-459, October 1944.
[2] Hives, E.W. and Smith, F.L., "High Output Aircraft Engines," SAE Journal, Vol. 46, No. 3, pp. 106-117, March 1940.

The sleeve material has to meet many criteria, however the essential requirement was identical thermal expansion at the sleeve OD and barrel ID interface. To make it more complicated the later Hercules and Centaurus had tapered bores. I understand that the clearance had to be 0.8 thou around the entire bore. In the paper I attached earlier, Mr Evans from Bristol stated " I would say that sleeve and barrel clearances are almost negligible. The sleeve is almost a push-fit in the barrel, but there is no difficulty in producing sleeves and barrels to the tolerances we require." p657. He earlier stated "With the sleeve valve the difficulty has always been to prevent over-lubrication, but we have been able to cope with the problem. As an instance, I would mention the sleeve valve or sleeve ball rig which we use on a mechanical breakdown test. Mr. Mansell had a great deal of trouble with overflow from the sleeve of this rig, and we had to fit a cover. The single sleeve acts as a good oil pump, unless the oil flow is controlled at the bottom end." p655. Thus a lack of oil is not an issue and there is likely not enough space for a void bubble to form.

The KE965 is a cast austentic stainless steel, and thus has a relatively poor thermal conductivity. Many years ago I worked on a DN600 stainless pipe that had to span 22 metres between supports. From 11 AM until around 3 PM during construction (i.e. empty) it would lift off one of the supports, due to the sunlight on top causing far more thermal expansion than the underside. More recently I had a cat dump line from an FCCU that would snake a large distance (~2" for an 8" pipe) in a different direction every time it dumped the 1300°F catalyst. The only saving grace for the sleeve is that it is rather thin - a poor conductor across a short distance does not result in a significant temperature delta.

In the Fedden paper you mentioned, the quote is: "The heat differential between the piston and cylinder, via the sleeve, is of the order of 40-50°C, clearly bringing out the limitations of this material from a conductivity point of view, although it is good from expansion, hardness and wear aspects. "
In my calc, the heat differential between the combustion gases and the sleeve wall (assuming piston has passed) was around 50°C due to the convection losses.
Understanding the heat conduction between the ring land area of the piston, through the ring and sleeve and into the barrel is way out of my league.
The Hercules (possibly only the later ones) and the Centaurus had oil cooling jets directed at the pistons. I understand in Lycoming GSO-480 engines, this dropped the piston temperature by around 200°F. The jets appear to shoot towards the centre of the piston, so I don't know whether this was able to lower the temperature in the ring land region where the problem is. (I am currently looking at why the Sea Fury engines keep failing, and ring deposits & incorrect dispersants is one rabbit hole that is taking a long time to investigate.)
Ricardo in both the 4th and 5th edition of his work (i.e. post war) states:
"Again, later tests, when the technique of measuring piston temperatures by means of fusible plugs had been developed, confirmed that the piston temperature in a liquid cooled single sleeve-valve engine was actually a little lower than in a poppet-valve engine of the same dimensions and output."
I do note that he deliberately nominated liquid cooled. Whether that was due to the test only being done on liquid cooled engines or it did not apply to air cooled engines is not clear.

TLDR: I don't think bubbles in the oil film are likely.

 

[Shortround6]

The sleeve acting as an oil pump of sorts may be quite true.

Part of our problem in sorting out the sleeve valve situation is that often the reports are snapshots in time. What was true late in WW II was not true early in WW II, or what was true in the 1950s.

Oil consumption was quite problem with the early Hercules, to point of oil fouling the spark plugs, More than an annoyance in overwater flights. It was solved, but the claim that all the Sleeve valve problems were solved in 1933 or even 1938 doesn't hold up.

I don't have a good timeline for the later Hercules and Centaurus engines. The last engine types appear to have been built between 1953 and 1956 ( I don't have the 1954 and 1955 editions of Aircraft engines of the World) and the 663, and 673 (?) show up in the 1956 book but not the 1943 book. Also showing up in the 1956 book is a listing for the 373 and 873 which were intended for the Blackburn Beverly but never fitted (if indeed they were ever built?)

with around 10 years of development after WW II quoting performance specs needs to done carefully. On both sides.

 

[Bretoal2]

The Knight engine used two sleeves and was quite successful as far as sleeve valve engines go.

Yesssss... with very low BMEP and power ratings, and enormous oil consuption !

 

[ThomasP]

Some interesting info on the Knight engine:

"Knight engine - Wikipedia"

"Knight and Day"

 

[don4331]

Second possibly stupid question for the day: was there any particular advantage of sleeve valves for the H-24 engine layout, or 24 cylinder engines in general?

I know with 2-row radials it was harder (not impossible) to make 4 poppet valves per cylinder work, compared with single row radials or V-12s.

Is there any similar logic for why Napier and RR went for sleeve valves on the Sabre and Eagle (also the X-24 Exe and Pennine) despite not being 'all in' on sleeve valves for everything like Bristol was? Alternatively it could just be a coincidence of two technologies coming into vogue at the same time, but it's interesting that RR kept playing with it late war when the Bristol radials and Sabre had been so troublesome and RR had done so well with poppet valves.

Possibly relevant:

• In older H-24s the Napier Dagger had 2 poppet valves per cylinder and the Fairey Monarch 3. The X-24 Vulture had 4.
• The Wiki Sabre page says: "The layout of the H-block, with its inherent balance and the Sabre's relatively short stroke, allowed it to run at a higher rate of rotation, to deliver more power from a smaller displacement, provided that good volumetric efficiency could be maintained (with better breathing), which sleeve valves could do.[6]" Which I understand as saying sleeve valves help you turn high revs which is often (not always) the goal with 24 cylinder layouts?

Epiphany moment: How do you fit the 2nd spark plug on H-24 with poppet valves?

With sleeve valves, you put the 2 plugs in the junk head side by side. Plugs are more/less in ideal location - center of combustion chamber, this allows designer to keep the vertical height of engine to a minimum.

No worrying about case where one plug doesn't fire, and then flame front doesn't make it to far side of combustion chamber; no concern with pressure spike when 2 flame fronts meet; no concern that the flame front is going to make it to far side of cylinder fast enough for maximum efficiency.

RR, for Kestrel/Peregrine/Merlin/Griffon/Vulture, puts 1 spark plug between intake valve pair and 1 between exhaust valve pair. Not ideal, but with their "bathtub" combustion chamber, it works pretty good.

With poppet valves there is no access for exhaust side spark plug in H layout unless your space the 2 crankshafts sufficiently far apart - you can see how much wider the Fairey Monarch is. The increased frontal area might be OK for a bomber. But, it isn't going to cut it for a fighter.

*You can change the 2nd spark plug position to center of all 4 valves, but there isn't a lot of space - you need to reduce the size of the intake and exhaust valve seats and/or springs = smaller valves = lower volumetric efficiency. And you need to add (and seal) a tube through the valve cover for spark plug, not to mention the cam (and followers) in the RR SOHC design are right where we now want to put our spark plug. So, you are talking a major packaging of the head. And RR has a bad memory of the ramp head not working on early Merlins - this is much more extensive shuffle.

 

[wuzak]

If they changed from SOHC to DOHC they would have space to put one spark plug, at least, on top of the cylinder head.

 

[Bretoal2]

Epiphany moment: How do you fit the 2nd spark plug on H-24 with poppet valves?

See Dagger...

 

[don4331]

If they changed from SOHC to DOHC they would have space to put one spark plug, at least, on top of the cylinder head.

DOHC moves the cam out of the way, but you haven't resolved the issue of no space between the 4 valve springs for the spark plug tube. And WWII airplane spark plugs aren't the slim things that automobiles use today.

See Dagger...

Yes, Dagger is another example of having to spread the cylinder blocks further apart to be able to package all the components. It's even worse than Monarch.
Monarch has the crankshafts interfacing the propeller reduction gear at roughly 8 and 4 o'clock positions - which has advantage of raising propeller.
Dagger had the crankshafts at 9 and 3 - as far apart as possible and still engage.

Napier Sable has the crankshafts as close as possible without interfering, therefore needing lay shafts between the crankshafts and propeller gear
RR Eagle meshes the lower crankshaft to the upper and then the upper to the propeller reduction gear. Again allowing the crankshafts to be very close together.

 

[Deleted member 68059]

Plugs can go in from the top as per Jumo-213J, on either side of the inlet valve springs, they come out into the chamber in quite nice positions.

 

[cammerjeff]

On the Dagger they seem to go on the sides of the combustion chamber, as per Snowygrouch's suggestion

Source Wiki

 

[Shortround6]

Cylinder block spacing was more defined by the crankshaft swing than the sparkplug spacing

Sabre engine.
The Sabre spark plugs were not all that easy to change.

 

[wuzak]

Yes, Dagger is another example of having to spread the cylinder blocks further apart to be able to package all the components. It's even worse than Monarch.

The Dagger wasn't exactly a wide engine. It was 22.5 inches wide, compared to the Merlin ~30in and the Monarch 43in.

Monarch has the crankshafts interfacing the propeller reduction gear at roughly 8 and 4 o'clock positions - which has advantage of raising propeller.
Dagger had the crankshafts at 9 and 3 - as far apart as possible and still engage. propeller reduction gear. Again allowing the crankshafts to be very close together.

Why is raising the propeller an advantage?

The Sabre had complicated reduction gear so that the propeller was in centre of the engine, half way between the upper and lower crankshaft axes.

The Monarch was two separate engines in a single package.
The left and right halves weren't geared together, and the halves could be operated independently. That made the reduction gear simpler.

The Dagger, on the other hand, had the crankshafts geared together. Which meant it could have:

the crankshafts as close as possible without interfering, therefore needing lay shafts between the crankshafts and propeller gear

 

[Bretoal2]

A Dagger section.

OHV and OHC (with automatic hydraulic tappets) , but combustion chamber is rather flat, and valves angle low.

And spark plugs are diametrically opposed.

 

[Reluctant Poster]

A Dagger section.

OHV and OHC (with automatic hydraulic tappets) , but combustion chamber is rather flat, and valves angle low.

And spark plugs are diametrically opposed.

That is fascinating. The British propensity for complication (think BRM V-16 and H-16 Grand Prix engines) is apparent. My personal favorite is the North British Sliding Cylinder marine diesel.
You can read about it here:

https://acwhyte.droppages.com/downloads/research/research_note_ms_swanley_and_nbsc_engine.pdf

 

[WARSPITER]

I've always found the rotary engines of WWI to be fascinating too.

 

[cammerjeff]

I've always found the rotary engines of WWI to be fascinating too.

I agree and the odd Siemens-Halske counter rotary engines just amaze me, with the crankshaft rotating in one direction, and the crank case rotating in the opposite direction, it took some time for me to figure out how you actually bolt the engine onto the aircraft!

 

[basil]

Could it be that the sleeve valve engine would have been particularly well suited to the two-stroke principle due to its lower tolerance for supercharging but higher rpm potential? I am thinking of the RR Crecy and subsequent projects from RR (24 cylinder two-stroke) as well as concepts from Tresilian. A particularly recommended read on this is "The RR Crecy" by RR Heritage Trust.

 

[Writer]

Very little attention seems to be given to the weight of the engines spoken about here. Given that the Rolls-Royce Griffon, in Mk VI form, gave well over 2,000 BHP, makes it a rival to the Napier Sabre. The Mk VII Sabre weighed 2540 pounds, the Griffon just 1790 pounds. I am an admirer of the Napier Sabre, (I read Setright's "The Power to Fly" at an early, impressionable age!), but it certainly would appear that the Griffon was the better choice....