Question about ADI and MAP

[ShortyDoowap]

F4UDOA’s question was:  The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?

The answer was that its fuel charge was sufficiently cool to avoid detontation at that manifold pressure.    In the P-51’s case, it was due to a very efficient aftercooler.

[gripen]

Originally posted by ShortyDoowap
In tests the R-2800 B series ran at 150" hg, developing well over 3,000 hp.

That was bench test with special cooling devices as noted above.

Originally posted by ShortyDoowap
The T-bolt was authorized to operate at 64" hg, and could tolerate 75" hg for several hours.

As noted above the P-47D required modifications to reach 64". The limiting factor was cooling of the heads which was also the reason why P&W redesigned entire engine during war.  

Below are the ratings used by 8th AF at spring 1944 (they had their own ratings). Note that modifications were required even for increase from 58" to 61".

Originally posted by ShortyDoowap
There was nothing inherently wrong with the Corsair's engine. (Now I am saying that.) It just appears the limits of its intercoolers and ADI system to cool the charge had been reached for 100/130 grade fuel. Had someone endeavored to install a larger ADI reservoir and increase ADI flow to the engine, or undertaken a more difficult task of increasing intercooler efficiency, then 67" could have easily been obtained.

As noted above the F4U-1 was tested at 65" with similar modifications as used in the P-47 (increased water flow). Below is a bit from Slaker's site showing use of the 65".



Such rating was not authorized for service use probably for cooling problems.

Originally posted by ShortyDoowap
F4UDOA’s question was:  The P-51 however uses no ADI. So how does the P-51 V1650-3/7 attain such high MAP with no Anti-detonate?

The answer was that its fuel charge was sufficiently cool to avoid detontation at that manifold pressure.    In the P-51’s case, it was due to a very efficient aftercooler.

As noted above by several people, the main reason were:

1. Compression ratio

2. Good cooling of the heads.

3. Charge cooling.

As noted above, the charge cooling was not needed in single stage Merlins for +18lbs which underlines limitations of the B-series R-2800. The engine stage of the R-2800 supercharger compressed air at amount less than 2 at 60" while the super charger of the single stage Merlins compressed air at amount over 3 at +18lbs.

gripen

[ShortyDoowap]

That was bench test with special cooling devices as noted above.

Just water injection.  That’s all it took.

As noted above the P-47D required modifications to reach 64". The limiting factor was cooling of the heads which was also the reason why P&W redesigned entire engine during war.  

Of course it needed modification.  Whenever a boost increase is needed, some sort of modification is required.

Below are the ratings used by 8th AF at spring 1944 (they had their own ratings). Note that modifications were required even for increase from 58" to 61".

If the original boost had been limited to 42”, it would have required modification to achieve 58”.  Do you know how a P-47 throttle works?  


BTW:

As noted above the F4U-1 was tested at 65" with similar modifications as used in the P-47 (increased water flow). Below is a bit from Slaker's site showing use of the 65".

Such rating was not authorized for service use probably for cooling problems.

Yet nowhere in the report from which that excerpt comes does it state the Corsair overheated.




 

As noted above by several people, the main reason were:

1. Compression ratio

2. Good cooling of the heads.

3. Charge cooling.

As noted above, the charge cooling was not needed in single stage Merlins for +18lbs which underlines limitations of the B-series R-2800. The engine stage of the R-2800 supercharger compressed air at amount less than 2 at 60" while the super charger of the single stage Merlins compressed air at amount over 3 at +18lbs.

gripen [/B]

LOL, why does the capability of the Merlin “underline” a limitation of the R-2800?  In fact, there was no inherent limitation.  As stated, the engine was perfectly capable of 67” or more on 130 grade fuel as long as the charge was kept cool enough to avoid detonation.

You could have taken the Corsair and made no other alteration to it except increase the flow of ADI and link the throttle to achieve 67” and it would have been perfectly capable of achieving 67”.

[pasoleati]

Check Torque Meter issue "Volume 2, NUmber 3", page 18. It has Fuel-air ratios for various engines at various airflows. It clearly shows than on a same fuel the V-1710-111 needs far leaner charge to operate at high power settings than even a C-series R-2800 (that had much better head cooling due to forged heads as Gripen said) as it requires far less overrich mixture as internal coolant. Thus there is substantial difference in their respective cooling capabilities.

[pasoleati]

Flakbait claims that 450 deg F (232 deg C) was supposedly a temp limit for aluminium heads. That is wholly untrue. E.g. the Centaurus V (that has aluminium heads) has a maximum continuous lean mixture limit of 300 deg C. The Centaurus tolerates the higher temperature due to the vastly better sleeve concept.

[ShortyDoowap]

As noted above, the charge cooling was not needed in single stage Merlins for +18lbs which underlines limitations of the B-series R-2800.

So the charge cooling (aftercooler) was not needed in the single stage Merlins.  The Mustang didn't have a single stage Merlin.  The Mustang's Merlin had a two-stage supercharger.  Two stages compress much more, and impart much more heat, than a single stage supercharger.   Therefore, an aftercooler was required on the Mustang's two stage Merlin.

[pasoleati]

According to "Rolls-Royce and the Mustang" by David Birch, the charge temp in a 60 srs Merlin (probably at +18lb) was reduced from 200 deg C to 120 deg C by the aftercooler. I.e. where did the 180 F figure originate from? That 120 deg C figure is also mentioned in the Spitfire bible.

[ShortyDoowap]

The pic comes from "Vees For Victory" from the chapter The Rolls Royce Merlin V-1650 vs. the Allison V-1710.

The text of the book states air discharged from the supercharger discharged at 396o F.  The temperature of the charge injected into the engine "never exceeded 212o F."

[gripen]

Originally posted by ShortyDoowap
Just water injection.  That’s all it took.

That was a bench test, certainly not with the engine installation of the P-47 or F4U/F6F.

Originally posted by ShortyDoowap

BTW:

There apparently was problems because 75" or anything over 64" (grade 130 fuel) was not authorized by USAF. Besides that might had been bench testing again.

Originally posted by ShortyDoowap

Yet nowhere in the report from which that excerpt comes does it state the Corsair overheated.

Well, there apparently was problems because such rating never entered service. And P&W improved cooling of the heads large amount in the C-series R-2800.

Originally posted by ShortyDoowap

LOL, why does the capability of the Merlin “underline” a limitation of the R-2800?  In fact, there was no inherent limitation.  As stated, the engine was perfectly capable of 67” or more on 130 grade fuel as long as the charge was kept cool enough to avoid detonation.

The single stage Merlins could reach without charge cooling  67" and compress charge more than 1,5 times more than  B-series R-2800 in the F4U-1 (neutral blower ie single stage configuration 54"). That underlines very well the effect of the good head cooling.

gripen

[ShortyDoowap]

Still, the answer to the question is its fuel charge was sufficiently cool to avoid detontation at that manifold pressure. In the P-51’s case, it was due to a very efficient aftercooler.

[gripen]

I wonder if you could ever admit that cooling of the heads and compression ratio  can explain the difference as well or better than the aftercooler.

gripen

[niklas]

Hi

I just compared P-51D climb chart with 1650-7 to F4U-4 engine operating chart with a 2800-18 engine

In 8 minutes, the 1650 burns
13 gal @ 47"
22 gal @ 61"

the 2800 burns
27.2 @ 47"
37.6 @ 60"

The MAP is comparable. Now the interesting is increase of fuel consumption from 47" to 60" or 61"

1650: +70%
2800: +40%

So there are 2 possibillities:
1)  the 1650 needs much more fuel at high power
2) the 1650 is much better at cruising settings.

I found some power specs and the ratio of the PW2800 to the V1650 is at given MAP:
@47" : 1700/1050 = 1.61
@60" : 2500/1490 = 1.67

So the ratio stays close together, what does not support possibillity 2. There remains possibillity 1: The V-1650 needs much more fuel at high power settings in relation to the power gain, and imo this can only explained by one theory: Without the possibillity of waterinjection, the V-1650 must use a large amount of the fuel for innercooling effects at high power settings.

niklas

[ShortyDoowap]

Originally posted by gripen
I wonder if you could ever admit that cooling of the heads and compression ratio  can explain the difference as well or better than the aftercooler.

gripen

If you took the aftercooler off the two stage merlin, would 67" have been possible on 100/130 PN fuel????????

[gripen]

Originally posted by ShortyDoowap
If you took the aftercooler off the two stage merlin, would 67" have been possible on 100/130 PN fuel????????

The V-1710 could do about same total pressure with intercooler and still having   lower SFC than Merlin. So if assume that RR had choosen same approach as Allison and P&W, the resulting two stage Merlin would have needed more intercooling capacity and installation to airframes, allready in production, would not have been so easy.

gripen