Does fuel grade effect HP?

[F4UDOA]

I have a question about the use of higher grades of fuel in relation to American Aircraft.

Does the use of higher grade fuel create higher HP?

I believe it does because this would raise allowable MAP and there by increase output BHP.

[gwshaw]

Originally posted by F4UDOA
I have a question about the use of higher grades of fuel in relation to American Aircraft.

Does the use of higher grade fuel create higher HP?

I believe it does because this would raise allowable MAP and there by increase output BHP.

Higher octane doesn't raise power by itself, but it does increase allowable MAP which does increase power.

Here are a couple of formulas you may find useful.

Convert octane rating to PN
2800 / (128 - octane rating) = PN
2800 / (128 - 96) = 87.5

MAP rating with changes in PN
((old MAP - 7) * new PN/old PN) + 7 = new MAP
((60 - 7) * 150/130) + 7
53 * 1.15 + 7 = 68.15 in Hg

PSI boost > Inches Hg
(Psi * 2.04) + 29.92
(15 * 2.04) + 29.92
30.6 + 29.92 = 60.52 in Hg

Greg Shaw

[GScholz]

No. 87 octane burns just as good as 100. However, 100 octane can be compressed more without detonating (known as "knocking" and like in diesel engines) allowing for higher boost levels. Running an engine on higher octane fuel does not give it more HP, you would have to modify the engine (increase turbo/blower charge and fuel injection) to make the engine produce more HP. It would be correct to say that higher octane fuel will allow the engine to produce more HP by increasing boost pressure.

[Flyboy]

so if a engine is modify to X octane
and then i degrade the octane
will the emgine loose power?

[GScholz]

The fuel would detonate (self combust due to the heat from the compression in the cylinder) this would damage the engine if boost is not reduced quickly. Potentially the engine could explode.

[Furious]

More importantly, and I think this is what GScholz is trying to say, is that it will pre-detonate.

[Staga]

Well not explode but continuous self-detonation of the fuel will broke up the bearings and in some cases gaskets too.
I've seen a piston from aircooled Deutz engine which over heated and begun to detonate 'cause of that.
Pistons looked like a rat had been eating them, cylinder head gaskets (copper rings in separate cylinders) lost their shape, oil (high grade synthetic, not some cheap mineral oil) turned to black stuff which was looking like toffee... that was the end of that engine.
I had one of the pistons as an ash tray thought I haven't seen it in years, guess someone thought it looked cool or something...

[GScholz]

Oh it will explode if the pre-detonation (thanks Furious) is very bad (like if you run a 150 octane engine on 87 octane at full boost) and the engine is running high rpms. It would tear itself apart.

[GScholz]

Originally posted by Staga
I had one of the pistons as an ash tray thought I haven't seen it in years, guess someone thought it looked cool or something...

I use a 155mm artillery shellcasing. It stands on the floor and it takes quite a while between times I need to empty it.

[SFRT - Frenchy]

You can always use higher octance of fuel, never lower than it's supposed too.

[F4UDOA]

I have another question then.

In your opinion are these HP ratings from 115/145 or 100/130 fuel?

These engine ratings are from the same engine. PW-R2800-18W from the F4U-4

[Vermillion]

Are you asking if the first page or the second page (or both) is using 100 octane fuel?

The second page in the bottom right corner states that the Fuel Grade is 100/130, AN-F-28.

The first page looks like the Notes page from one "Standard Flight Characteristics"  pdf docs off the Naval Aviation History site ( http://www.history.navy.mil/branches/hist-ac/f4u-4.pdf )

And if you look a few pages before in the "Fuel & Oil" section (page right after the 3 view diagrams) that it states that the fuel grade is 115/145 and fuel spec is AN-F-48

Does that help?

[GScholz]

I have nooooo idea. Can't even begin to figure out the math involved in finding that out.

[F4UDOA]

Verm,

That is exactly my point.

You are right that is the NAVAIR F4U-4 doc and the second one is from the flight manual. Point being they both have the same HP curve.

My point is that the flight test done in the NAVAIR doc was not done with 115/140 fuel.

Another way to show that is the speed of that F4U at sea level is identical to that shown in the AH charts. If the MAP were higher then the speed would be higher at sea level as well.

By that I mean the sea level speed in AH is 376MPH combat. The speed in the PDF is 374MPH.

So the test where the F4U is supposed to be overboosted it is actually slower than the standard boost while climbing 1K per minute better. Something doesn't add up.

[DiabloTX]

Originally posted by GScholz
I use a 155mm artillery shellcasing. It stands on the floor and it takes quite a while between times I need to empty it.

Bloody good idea!  Think I will get one myself!  Thanks, GS.