Engine sputter / detonation with low power settings ...

[Solty]

I use the source available and this relies on the documents from the period. I do not notice any form of bias there. If you are able to disprove/dispute any of those reports, please do. But if there is no proof that this archive is wrong, then it should be assumed that what we have in front of us is true.

[Echo38]

I think you missed my point. My point wasn't that we should assume that it's wrong; we have no reason to do so. Rather, we should be attempting to cross-reference with other sources. That's the academic way of doing things, regardless of where the original source came from. Multiple sources saying the same thing is better than always the same source saying the same thing. That's the basis of research.

 

So, my apologies if I didn't convey my point clearly. My point is not to undermine Mr. Williams' site as a source; my point is, we really ought to try to find another source with which to cross-reference. That's just how research is done, at least in academia.

 

In other words: our position regarding certain topics would be stronger if we had two independent sources in agreement, rather than always falling back on the same one source. See?

[Solty]

Then present your source... As I said, you can confirm it, or disprove it. It is based on real life reports. So, if you have another source, go ahead and show it.

 

The nature of the topic beeing top secret USAAF documentation of 1940's implies that sources are scarce and therefore I am using what I can.

[Crumpp]

One last thought on the matter (Sith...please bear with me :)).

 

This explanation is quite correct for a "pop" that is heard when throttling back:

 

 

 

I have a new 2015 (fuel injection, variable valve timing, catalytic converters, etc - it's a bone stock new car with a warranty) car that does this on throttle lift (generally lifting between 2000-3500 rpms and more prevalent after periods of aggressive operations). You can't even change the air filter on this thing without triggering a check engine light and it is definitely running properly.

 

Even in a modern car with fuel injection and mass air sensors, there is a very brief lag between closing the throttle and the air-fuel mixture adjusting. A bigger concentration of unburned fuel travels through the exhaust and ignites upon reaching the exit (where oxygen is present). At night, you can see flames appear for a split second, but generally you just hear a pop.

 

It doesn't harm anything since it's happening at the exhaust exit (like firing blanks in a rifle) and no significant pressure is generated. Race cars do it all the time (more so than street cars) and you only see it during off throttle periods.

 

There may be other things that cause "pops" like this, but Sobek's explanation is definitely accurate and does not represent improper tuning or a bad gasket.

 

Not sure if this is the cause of of the sputter heard with the P-51, sounds like I might need to check things out.

 

It's awesome that DCS depicts all of these nuances of piston engine operations, this is far more sophisticated than I would have expected. I might need to spend more time in the P-51D (I tend to prefer the FW190 D-9 and BF109 K-4).

 

-Nick

 

:music_whistling:

 

After-Firing in Exhaust System:

 

After Fire may result in rupture of part of the exhaust system and should be corrected immediately. It is usually caused by one or more of the following:

 

Malfunctioning ignition system

Sticking intake valve

Misfiring engine

Leaks in the intake system

Incorrect valve timing

 

 

https://books.google.com/books?id=SPI6AQAAMAAJ&pg=PA183&lpg=PA183&dq=afterfiring+valve+timing&source=bl&ots=c_jW5ZIjpi&sig=1IOdBi7f-Wj1CauromNLDryAVcU&hl=en&sa=X&ved=0ahUKEwinkPfdz6fJAhWK7CYKHbrOBa8Q6AEIKDAB#v=onepage&q=afterfiring%20valve%20timing&f=false

 

Solty, please read what you quoted. The PEP was introduced to try and stop the plug fouling issues of the original fuel.

 

PEP was even worse for the engines and they went back to using the original fuel even with its plug fouling issues because it was safer than PEP.

 

150 grade fuel continued to be used by 8th AF units through 1944. 31 The WER engine limitation for the P-51 continued to be 72" Hg. 32 Eighth Air Force Fighter Groups converted to a new blend of 150 grade fuel, with increased amounts of ethylene dibromide (1˝ T) in early 1945. 33 P.E.P, as the new fuel was called, was tried in order to remedy lead fouling of spark plugs. While spark plug fouling was eliminated, PEP was found to have an undesirable effect on valve seats. As a result of excessive maintenance required on the V-1650 engines, General Doolittle of the Eighth Air Force decided in late March 1945 to revert to the normal 100/150 (1 T) grade fuel. 34

 

The plug fouling problems are from British 100/150 grade as used by the RAF ADGB, 2nd TAF, and 8th USAAF.

[Crumpp]

At night, you can see flames

 

BTW...

 

You can see flames appear in any engine with straight pipes if the exhaust is short enough.

 

Nothing at all to do with the impulse collapsing causing the popping noise.

 

Just look at the P-51 POH Fredrich posted. The color was a good indication of the correct mixture setting.

[sobek]

Nothing at all to do with the impulse collapsing causing the popping noise.

 

How many people (including Yo-Yo btw.) does it take to tell you that you're on the wrong track?

[Solty]

@Crump

 

150 grade fuel continued to be used by 8th AF units through 1944. 31 The WER engine limitation for the P-51 continued to be 72" Hg. 32 Eighth Air Force Fighter Groups converted to a new blend of 150 grade fuel, with increased amounts of ethylene dibromide (1˝ T) in early 1945. 33 P.E.P, as the new fuel was called, was tried in order to remedy lead fouling of spark plugs. While spark plug fouling was eliminated, PEP was found to have an undesirable effect on valve seats. As a result of excessive maintenance required on the V-1650 engines, General Doolittle of the Eighth Air Force decided in late March 1945 to revert to the normal 100/150 (1 T) grade fuel. 34

 

And what fuel was it using in 1944? 100/150 44-1. So they have reverted exactly to the same fuel they had before and used till early 1945.

 

So basically, they flew on a fuel that is needed to be in DCS to achieve 72' or 75',up to the end of 1944, and our game is called DCS 1944. And remember that British used 81'hg MAP.

 

Also, fouling is not only a problem of Merlin engine, I wonder how Germans faired :D Anyone has German maintnance reports about late DB605 engines with B4 and C3 fuels of 1944?

[Crumpp]

How many people (including Yo-Yo btw.) does it take to tell you that you're on the wrong track?

 

I do not see where Yo-Yo says anything wrong. Combustion in the exhaust is the cause of after-firing NOR do I see where he agrees you are right so do not drag him into it.

 

 

It is a common misconception when dealing with straight exhaust systems. I am not surprised it is controversial on an internet bulletin board.

 

If the was the Aviation Maintenance Technician bulletin boards, it would be a short thread.

 

The basic premise you stated for the cause of afterfiring is correct and several others have repeated that same cause.

 

I told you that the first post.

 

The differences is your claim that is it "normal" and that nothing else causes the popping sound. That is just wrong and an incomplete picture.

 

1. Normal popping noises heard in straight exhaust systems is not afterfiring. It is the collapse of the pressure impulses.

 

2. Afterfiring is not a normal condition. It represents a condition that needs to be troubleshot and corrected.

[Crumpp]

So they have reverted exactly to the same fuel they had before and used till early 1945.

 

Correct, the one that caused all the plug fouling and crashes. Desperate huh? You can see why the technical side never would recommend the fuel.

 

 

However, the 8th USAAF fighters never used 75"Hg and used the fuel in late 1944 sometime after Overlord. It is not the majority of the USAAF P-51's in the ETO either.

 

It should be an option when we get bombers to escort.

 

I think it would be a good option in the drop down menu just like the both German fighters can select fuel or MW50 in the fuselage tank.

 

The instructions for 8th USAAF P-51's to avoid the excessive lead fouling was to carry 100/130 grade for external fuel and fill the internal tanks with 100/150 grade. It could be an option when you select external tanks in the drop down menu.

[MiloMorai]

As a result of several months operational use with the fuel, an SOP – designed to reduce power failures on take-off, leading troubles in flight, and other things which were causing early returns and abortive aircraft – was published. This is inclosure no. 1. Almost immediately after this section published this SOP practically all of the troubles then existing ceased, although it was necessary to change plugs after each two missions or thereabouts.

 

http://www.wwiiaircraftperformance.org/150grade/Consumption_150_Grade_fuel_Barrels.html

 

From June 1944 to year end that was 47,950,000 Imp gal of fuel consumned. If the 8th AF wasn't using the fuel then it must have been the RAF.

 

As for your graphic in Post #54 that is for normal running of the engine, NOT when the throttle is chopped. If you are an A&P as you claim, you would know that their would be raw fuel in the exhaust especially with the rapid closure of the throttle.

 

British Mustang IVs (P-51D/K) were using 25lb boost.

[Crumpp]

As for your graphic in Post #54 that is for normal running of the engine, NOT when the throttle is chopped. If you are an A&P as you claim, you would know that their would be raw fuel in the exhaust especially with the rapid closure of the throttle.

 

 

So now the argument becomes reducing the throttle is not NORMAL operation of an engine.

 

 

:doh:

[Echo38]

Then present your source... As I said, you can confirm it, or disprove it. It is based on real life reports. So, if you have another source, go ahead and show it.

 

You aren't listening to me. Stop reading in between the lines for a hidden message; there isn't one. I meant what I said--nothing more, nothing less. So, again: do we have another source to cross-reference with? I don't, and I'd like to.

 

So basically, they flew on a fuel that is needed to be in DCS to achieve 72' or 75',up to the end of 1944, and our game is called DCS 1944.

 

72" was able to run, and was authorized to run, on 100/130. 100/150 wasn't required for 72".

Edited November 26, 2015 by Echo38

[MiloMorai]

So now the argument becomes reducing the throttle is not NORMAL operation of an engine.

 

:doh:

 

:cry: Normal like if you are cruising down the road and your vehicle starts doing what is said in the graphic.:wallbash: