Octane rating

[JohnDillworth]

Does anyone know the average octane ratings that were available to the Allies and Japan? I am under the impression that the IJN and IJA planes used gasoline with a significantly lower octane rating. If this is true were the planes designed with that octane rating in mind? Would they have performed better with better gas? If seems towards the end of the war the best planes were roughly equal (Frank & P-51). Would better gasoline have made the Frank a much better plane?

[vettim89]

Waiting for it ................

[JohnDillworth]

Waiting for it ................

OK, what did I do? I didn't cross Terminus did I? Which old timer? Did I compare specific aircraft? I swear I only meant to illustrate my question.....Oh great....There is a knock at the door.....hold on .......Who the hell is WITPAE Black Ops? Helppppppppppppppppp.................

[Alfred]

American refineries were able to produce 100 octane fuel. Volume produced was sufficient to export it to allied countries. The Axis powers had to make do at best with 87/89 but that level was not always obtained, in the case of Japan dropping down to 81 octane in the second half of the war.

Not only could the American refineries get the high octane levels, they could do it more efficiently and at lower cost than the Axis.

To get the best out of the higher octane levels the engines would have needed to be specifically designed for it. Thus it is not simply a case of stating that the Frank with higher octane fuel would have flown better. Using is existing engine it would have seen an improvement in performance but the full benefit would be dependent on having the right engine for the fuel.

You know, those Americans were very gamey. The high octane was just one of several gamey actions which borked the war against the Axis.[:)] I'm often reminded about how most armchair generals just criticise the Italians for standardising with 840 hp FIAT engines for their airplanes without taking into account the real world constraints on their design options. Same issues often applied to the Japanese, which issues are never fully taken into account (in fact usually not at all) by people who argue how Japanese industry could have been reshaped to make better war materiel.

Alfred

[Buckrock]

ORIGINAL: JohnDillworth

Waiting for it ................

OK, what did I do? I didn't cross Terminus did I? Which old timer? Did I compare specific aircraft? I swear I only meant to illustrate my question.....Oh great....There is a knock at the door.....hold on .......Who the hell is WITPAE Black Ops? Helppppppppppppppppp.................

I'd guess you must have inadvertently dropped your aviation fuel question into the embers of some old fire and now people are waiting to see what happens next.

Lucky you have that avatar. [:)]

[Historiker]

ORIGINAL: vettim89

Waiting for it ................

I really don't have any intention to insult you and am really sorry, but isn't this almost trolling itself?
It annoys me every time, when those wise guys go into threads and don't contribute anything but "the trolls will come".

I know, calling someone a troll is one of the most harsh insults you can say in a forum, but again: Isn't that trolling by itself?

[:-]

[vettim89]

ORIGINAL: Historiker

ORIGINAL: vettim89

Waiting for it ................

I really don't have any intention to insult you and am really sorry, but isn't this almost trolling itself?
It annoys me every time, when those wise guys go into threads and don't contribute anything but "the trolls will come".

I know, calling someone a troll is one of the most harsh insults you can say in a forum, but again: Isn't that trolling by itself?

[:-]

Ok, to be clear: often when avgas is discussed, I see it immediately morph into a discussion about how the George or Frank were actually the best fighters of WWII if the IJNAF/IJAAF had access to higher octane fuel. I was just ading that comment so I could claim clairvoyance when it happened. Sorry, did not mean to offend. I guess I was just trying to be too much of a smart alek

[Historiker]

[:)]
I didn't try to offend, either! You were only the unlucky one to hear my first expression of annoyance about this common habbit in this forum.

[JohnDillworth]

A bit of background. I recently saw an article that claimed the use of American 100 octane fuel over the European 87 Octane allowed late model Spitfires to add 25-35 mph to their top speed depending on altitude thus winning the war. BS on the Spitfire even being important late in the war (could not escort bombers past the front yard)but I was curious as to the significant performance increase being reported. I presume the late model Spitfire was optimized for the 100 octane fuel because England was not refining too much of their own gas and basically using American supplies.

[mike scholl 1]

ORIGINAL: Alfred

You know, those Americans were very gamey. The high octane was just one of several gamey actions which borked the war against the Axis.[:)] I'm often reminded about how most armchair generals just criticise the Italians for standardising with 840 hp FIAT engines for their airplanes without taking into account the real world constraints on their design options. Same issues often applied to the Japanese, which issues are never fully taken into account (in fact usually not at all) by people who argue how Japanese industry could have been reshaped to make better war materiel.

Alfred

Like the inability of the IJN and the IJA to agree on a common electrical voltage for their A/C..., meaning they had to maintain two seperate and parallel electrical componants industries. This situation would never have been allowed in the USA.

[Erkki]

AFAIK the post war Allied(IIRC often with Japanese pilots though) performance tests performed using Allied fuels showed small but clear increase in performance, but still usually falling within 5%(performance variation typically expected between individual planes of same type) or so. I dont have a definitive source on hand now but digging the all knowing Internet for one shouldnt take long. [:D]

However as Japanese engines were most likely optimized to lower octanes(87, correct?), I believe having better fuels and engines made to use those fuels would have helped the Japanese fighters tested more.

[JWE]

Ok, I'll bite. Yes, technically, higher octane gives better (faster) cylinder deflagration characterists and, thus, more horsepower. More horse power means better performance. How much? Dunno. But even 5% is better than none.

But ... There's always a butt, isn't there? ... it also increases cylinder temperature. So if the engine isn't designed for it, then ... Hundreds of books have hundreds of examples of Germans, Czechs, Poles, French, Italians, finding a crashed Allied plane and draining some gas from the wreck for their motorcars. Yeah, AvGas in a car. About an hour later, they had a smoking ruin of melted engine header. Gee, wonder why.

You need 100 octane fuel to design an engine that runs on 100 octane fuel. The egg definitely comes first in this case. You can't just gas up an engine, designed with a particular specific heat in mind, with the good stuff, without a certain degree of unanticipated consequences.

[ed] spelling

[HMSWarspite]

Close but not quite. Octane rating correlates with the fuel's ability to resist premature ignition, with increasing compression ratio. Low octane fuels cannot stand the temperature cause by higher compression, and will 'knock', or detonate before the spark plug fires. This results in loss of power, or engine damage (the charge gives the piston a filthy great kick down as it wants to continue moving up, not to mention possible surface damage due to the detonation wave)). Running a low compression engine on high octane fuel does nothing - you need a higher compression ratio (i.e. significant engine mods) to get anything out of it. On the other hand, for a given engine envelope, higher compression means more horsepower...

[JWE]

Six of one, half dozen of t'other. I refer to it as better deflagration characteristics. But I defer to Mr Warspite.

[ed] The Winston Cup guys do tweak the ignition timing to accommodate the nifty, cool, additives they put in the gas. I think some of the cars are actually a degree ahead of TDC.

[wdolson]

The Reno Air Race guys tune their engines and make up their own mix of fuels for their planes. Some of the octane ratings are insanely high. Over 200 if I remember right. Some of the additives are so nasty the pit crews need to wear hazmat suits to handle the fuel.

The US made 100 and 140 octane fuel. 100 was the most commonly used, but some planes used 140. The B-29 is the only one I recall using 140 off the top of my head.

I know today they Europeans use a different calculation to come to octane ratings. A European 87 octane rating is closer to 91 by the American calculations. I ran into this with a friend who is a British immigrant and a motorhead. He was wondering why British cars performed better on lower octane fuels than the same car with the same engine in the US.

To elaborate on what Warspite said, the higher the octane rating, the slower burning the fuel is. A low octane fuel burns very quickly, so the cylinders basically get a quick hammer blow. High octane fuel burns slowly, so the cylinders get a smoother, longer push. That's why higher octane fuel gets more oomph out.

I know the Germans essentially had 87 and 91 octane during the war. I'm not sure what ratings the Japanese had. I wouldn't be surprised if they were going as low as 81 octane near the end. I know they were using turpentine for some fuel (probably a blend) at the end of the war.

Bill

[JWE]

Looks like no one is gonna answer your question Mr Dillworth. Too bad. It was a good one.

[JohnDillworth]

Looks like no one is gonna answer your question Mr Dillworth. Too bad. It was a good one.

I think I got most of an answer. Japanese planes used apx 87 Octane and Allied Planes used 100. Aircraft designed to use the 87 Octane will perform about 5% better (actually the 25 mph bump for spitfires is about 5% better)with 100 octane but the engines might not last as long. While the higher octane gas is "better" the 5% bump doesn't make much difference when you take into account other design decisions (guns vs. canons, armor vs. speed or range, training, maintenance). The only thing that still surprises me is that the Japanese were able to field excellent designs right until the end of the war. Considering their economy was no match for the US (or England or Germany for that matter)the fact that they could throw Georges or Franks into the mix at all is impressive. Thanks all

[Knavey]

ORIGINAL: vettim89

Waiting for it ................

Yup...so am I. Heard a rumor...

Its supposed to be in the next patch. You will get to determine what octane your planes use and it will effect performance!

[:D]

[PaxMondo]

Bill's answer is about as good as you can get without going into some pretty deep science. 
 
This is all off the top of my head, so apologize for any inconsistencies.  Octane numbers are a bit arcane.  First off it is a scale, it doesn't relate to reality.  100 Octane meant 100% N-Octane back in 1910 or so, so going over a 100 is kinda hard to understand.  It is all about anti-knock.   Then there are two ways to calculate this, research and motor (RON and MON).  The europeans and americans use a differently weighted average of the two to establish their scale.  Then, and even more importantly, is that how octane was boosted in the 40's isn't how it is done today.  Then it was about alkylation and so the octane boost was coming from n-nonane and n-decane type fuels.  Now, it comes from FCC and that gives you alkylenes like benzene and toluene to boost the fuel.  The amounts required to boost are different and how the impact cylinder temps are different.  They also behave quite differently under temperature and pressure as their partial pressure are different.
 
But a lot of this isn't as important as it seems.  Once you bring methanol/water injection into play octane become less of a factor.  Still a factor, yes, but less than you think.  Let's look at the chemistry and the mechanics here.  Engines are all about gas expansion forcing a piston to move down a cylinder and turn a crankshaft.  Igniting gas is good for about a 38x factor of expansion, not counting temperature effects.  That's awful good.  Water though is good for 18x.  The nice thing about water is that it take heat to move to steam, and this is how water injection works.  You start with an engine that is running too hot, you inject water to cool it and you actually get MORE power from it as the water expands into steam.  This works really well with radial air cooled cylinders as they are all more or less the same.  With in line water engines, you always struggle to get in inside cylinders as opposed the outside (on a V8 this would be 2,3,6,7 against 1,4,5,8) to be the same temperature.  The downside to water is that it is incredibly corrosive and impurities are very dangerous to metals (like chlorine and sodium as in salt).  Now add on superchargers and/or turbochargers (twinchargers) and again you get more complex.  On top of all of this is that in the 40's all they had was analog controllers. 
 
By wars' end the germans (extensively) and the IJ (Dinah and some other models) were using water/methanol.  This, when coupled with charging systems, mitigates the octane issue.

[witpqs]

ORIGINAL: PaxMondo

Bill's answer is about as good as you can get without going into some pretty deep science. 

This is all off the top of my head, so apologize for any inconsistencies.  Octane numbers are a bit arcane.  First off it is a scale, it doesn't relate to reality.  100 Octane meant 100% N-Octane back in 1910 or so, so going over a 100 is kinda hard to understand.  It is all about anti-knock.   Then there are two ways to calculate this, research and motor (RON and MON).  The europeans and americans use a differently weighted average of the two to establish their scale.  Then, and even more importantly, is that how octane was boosted in the 40's isn't how it is done today.  Then it was about alkylation and so the octane boost was coming from n-nonane and n-decane type fuels.  Now, it comes from FCC and that gives you alkylenes like benzene and toluene to boost the fuel.  The amounts required to boost are different and how the impact cylinder temps are different.  They also behave quite differently under temperature and pressure as their partial pressure are different.

But a lot of this isn't as important as it seems.  Once you bring methanol/water injection into play octane become less of a factor.  Still a factor, yes, but less than you think.  Let's look at the chemistry and the mechanics here.  Engines are all about gas expansion forcing a piston to move down a cylinder and turn a crankshaft.  Igniting gas is good for about a 38x factor of expansion, not counting temperature effects.  That's awful good.  Water though is good for 18x.  The nice thing about water is that it take heat to move to steam, and this is how water injection works.  You start with an engine that is running too hot, you inject water to cool it and you actually get MORE power from it as the water expands into steam.  This works really well with radial air cooled cylinders as they are all more or less the same.  With in line water engines, you always struggle to get in inside cylinders as opposed the outside (on a V8 this would be 2,3,6,7 against 1,4,5,8) to be the same temperature.  The downside to water is that it is incredibly corrosive and impurities are very dangerous to metals (like chlorine and sodium as in salt).  Now add on superchargers and/or turbochargers (twinchargers) and again you get more complex.  On top of all of this is that in the 40's all they had was analog controllers. 

By wars' end the germans (extensively) and the IJ (Dinah and some other models) were using water/methanol.  This, when coupled with charging systems, mitigates the octane issue.

When you say water/methanol, do you mean that the entire fuel was water/methanol, or that water/methanol was added to the avgas?