VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   Traditional Aircraft Engines (https://vansairforce.net/community/forumdisplay.php?f=21)
-   -   CHT - Angle Valve vs Parallel Valve (https://vansairforce.net/community/showthread.php?t=79961)

DanH 12-12-2011 11:03 PM

CHT - Angle Valve vs Parallel Valve
 
From time to time someone will mention that the parallel valve cylinders are harder to keep cool than angle valve cylinders. It's one of those things which seem plausible. However, evidence would be nice too.

Jeff Schans at Lycoming was kind enough to supply cooling air charts for the 4-cyl engines of interest to RVers. They are available (for now) at:

www.perryhillauto.com/downloads

Tonight I plotted a 4 inch H2O baffle drop at 5000 ft pressure altitude and 60 OAT for all four engines. Below you see the lower right corner of each chart:



Note the parallel valve charts have two CHT curves, 75% @435F CHT and full power at 500F CHT. The angle valve engines have three CHT curves, 70% @ 400F and 435F (425F for the IO-390), and a full power curve. I point this out because it's easy to get confused....look close at the labels. I've marked the 435F curve on each.

Apples to apples, you can just barely keep the 320 under 435 CHT with 4" of water across the baffles.

4" isn't enough for the parallel valve 360; CHT is heading for the absolute limit.

On the same 4" an IO-360 angle valve is around 420 CHT. To be fair the curve is drawn for 70% power rather than 75%. Even at 75% the angle valve 360 would cool as well as the little 320 on the same mass flow.

The 390 chart is plotted for 425F CHT rather than 435F. It appears they just shifted the curves upward a bit. You can even cool a 390 on the same mass flow as a 320.

So, parallel valve owners, the CHT problem is not entirely your imagination. Running "only" a 320 does not make the task easier. O-360 owners (and by extension O-540 owners) get no slack at all. They must have good baffles, good seals, and good upper cowl pressures or accept the consequences.

Lars 12-13-2011 12:33 AM

And the performance difference would be related to what... the oil spray nozzles applied to the pistons on the angle valve engines, which are lacking on the parallel valve engines? Or something else?

As always, thanks for posting.

Alan Carroll 12-13-2011 06:50 AM

Interesting stuff, thanks for posting. If I'm reading these charts correctly the parallel valve engines need something like 25-30% more cooling air to achieve the same CHT as the parallel valve?

On the other hand it would seem that the total heat production for the angle valve engine must be as great or greater than the parallel valve, assuming the same combustion temperature. This implies that the CHT cooling advantage of the angle valve must be balanced somewhere else, presumably in greater need for airflow to the oil cooler? If so then you still need tight baffles, if the oil cooler takes its air from above the engine.

DanH 12-13-2011 07:32 AM

Quote:

Originally Posted by Lars (Post 605340)
And the performance difference would be related to what... the oil spray nozzles applied to the pistons on the angle valve engines, which are lacking on the parallel valve engines? Or something else?

That's the common belief. Piston squirters certainly increase the percentage of waste heat being shed through the oil cooler.

I've also heard it argued that the angle valve cylinders have more fins or more effective fins. Anybody care to estimate the relative fin areas for the 360 parallel and angle valve cylinders? The charts suggest the 360-size angle cylinders do not have more passage area between the fins; the mass flows are the same (a little over 1.5 lbs/sec) for the same pressure drop and altitude. I suppose they could have more fins and narrower passages.

Quote:

Originally Posted by Alan Carroll (Post 605373)
If I'm reading these charts correctly the parallel valve engines need something like 25-30% more cooling air to achieve the same CHT as the parallel valve?

For equal CHT at 60F OAT I read required mass flow as:

320 1.45 lbs/sec
360 1.8
IO360 1.4
IO390 1.45

Quote:

On the other hand it would seem that the total heat production for the angle valve engine must be as great or greater than the parallel valve, assuming the same combustion temperature.
Yep. Two choices; the additional waste heat must leave town via the oil system, or by heating the cooling air to a higher temperature. One, the other, or both...right now I don't know.

Lars 12-13-2011 07:43 AM

Do angle valve cylinders have the same condition as parallel valve cylinders with lack of finning on one (intake) side? Or maybe that's not universal. The cylinders on my parallel valve 360 Superior engine are certainly lacking in that area- but maybe that's irrelevant to this discussion.

Given that most of us draw (or in my case, will draw once it's flying) air from the upper plenum to feed the oil cooler, it seems to me that good sealing is necessary in any case- any leakage (parasitic loss) takes away air that could have gone past the fins or through the cooler.

Bevan 12-13-2011 08:53 AM

At least on the side by side RVs, the cowl for the angle valve engine is bigger (wider) than the parallel valve engines. It may be (and would make sense) that the air inlets are bigger too.

Bevan

jjconstant 12-13-2011 09:55 AM

I was under the impression that the angle valve engines weigh 40lbs or so more and that weight included more cooling fin, but it also produces more heat (hp). Sounds like the ratio of heat production to heat rejection is better in the angle valves, but it costs more weight (and $!). I went for the higher compression ratio parallel valve as a cheat to "almost" angle valve power without fully appreciating the cooling issues. Thanks Dan for the research and facts. Great continuing education...

Jeremy Constant

hgerhardt 12-13-2011 08:23 PM

Quote:

Originally Posted by Lars (Post 605340)
And the performance difference would be related to what... the oil spray nozzles applied to the pistons on the angle valve engines, which are lacking on the parallel valve engines? Or something else?

As always, thanks for posting.

If you compare the angle-valve and parallel-valve cylinders side-by-side you'll see that the angle-valvers have substantially more fin area than the parallelers.

I can't believe that the piston cooling nozzles will lower CHT's... much... but they will certainly raise oil temps. And I definitely see that in my own airplane. I'm running a Stewart-Warner 8406R in my -6 with an IO-360-A-series and can count on one hand how many times the CHT went over 400 in 460 hours of use. But, I see oil temps over 240 pretty often.

1Oldguy 12-14-2011 08:25 AM

Fins
 
hgerhardt on the right path here. Set an angle value cylinder next to a parallel value cylinder and you will not beleive the difference in the number of cooling fins, more on the angle value cylinder. More area more heat is disapated, simple. The piston cooling nozzles are for, well, cooling the pistons :rolleyes:. That heat has to go somewhere right, like maybe into the oil.
I'm running an angle value 320 and it's a kick *** little engine. Lycoming should of made one. Great fuel economy and power out the wasszoo on the top end, just will not pull with the 360's down low in the rpm's. :mad:

Lars 12-14-2011 09:18 AM

I have not seen very many angle valve jugs, let alone seen an angle valve engine alongside a parallel valve engine for comparison. Since Lycoming saw fit to add a lot of fins and oil jets, they were obviously concerned about dissipating the waste heat from those extra 20HP :)

And apparently the fins work, since the cylinder head temps are maintained as well or better than on parallel valve engines, with less mass flow.

For the same power setting (absolute, not percent) does an angle valve engine require a larger oil cooler (more mass flow through cooler) than a parallel valve engine? If so, one could infer that it takes both fins and oil jets to keep things comfy. In other words, choice C on the list at the end of Dan's last post.


All times are GMT -6. The time now is 05:27 PM.