Use of 150 octane fuel in the Merlin (Xylidine additive etc etc)

In article ,
Dave Eadsforth writes:


Good day, good people,

I wondered if anyone out there (in all probability, Peter!) could help
me understand more fully the process by which the Merlin engine was
enabled to use 150 octane fuel; one feature of which was the addition of
the Xylidine anti-knock compound. (This was touched on in a thread
last year, I recall.)

If you can wait, I've got to dig out some files & make sure of some
references, but I'll have a comprehensive answer in about a day's
time. In the meantime, I'll chuck out a tidbit or two.


I understand that 150 octane fuel became available during 1944 - I don't
know when (a date would be welcome), but it was available in time to
boost the performance of those Spitfires that were assigned to knocking
down the V1s. What I would like to find out is what might have been
done to the Merlin to allow it to run on the stuff?

As far as engine modifications go, Not a lot, really, other than
changing the settings in the Manifold Pressure Regulators and possibly
tweaking the jets in the carburetors.

The higher engine output comes from the increased Manifold Pressure.
High Octane fuels tend to have a somewhat lower energy content than
those with lower Octane (or Performance) Ratings. (Technically, if
it's over 100 Octane, it's a Performance Number.) The energy
content's really not much of a difference, though, so we can skip it
for now. One of the consequences of increasing the Manifold Pressure
is a higher Charge Temperature (The temperature of the compressed air
in the Intake Manifold). If that temperature gets high enough, the
fuel-air mixture will self-ignite - Detonation - "Knock" is too kind a
word for what happens at +25 Boost when uncontrolled burning, and its
attendant shockwaves get going in a Recip's cylinder. The higher the
Performance Number, the more resistance to detonation, and you can use
the extra power that the higher manifold pressure gives you without
having to walk home.
Note that there are other alternatives as well, such as Anti Detonant
Injection, or Water Injection, where an aerosol of water, or a
water/alcohol mix, is sprayed into the air as it's benig compressed to
absorb some of the heat, and lower the Charge Temperature.


Was the use of 150 octane restricted to particular marks of engine?

As far as I know, it was mostly used on Spit Mk IXs with Merlin 66
engines. There were also some experiments with 150 PN fuel in Rolls
Griffons, and Packard Merlins, as well.

I read somewhere that it was supposed to provide an effective increase
in power of about 15 percent - by allowing a higher manifold pressure.
Is that figure of 15 percent correct?

I'll have real numbers for you in a day or so, but that sounds about
right. Of course, the increase in power comes with a decrease in
Critical Altitude - The supercharger can only compress things so much,
after all, so to get a higher Manifold Pressure, you've got to start
with thicker air.

Was the conversion to 150 octane done by merely adjusting the existing
arrangements for the supply of fuel, or was there a need for new fuel
supply components (carbs etc.)? And would the permitting of the
additional boost have mandated the exchange of some internal engine
parts (bearings, crankshafts, etc.)?

The bearings/cranks/conrods/pistons, etc, were stock components.
Teh carbs were teh same - but I don't know if they got tweaked. The
automatic Boost Pressure Regulators would, of course, need to be
reset. It was the sort of job that could be done at the Squadron,
rather than Depot, level. You didn't have to go in & rebuild
anything. I'd prefer to start with an almost new engine, however. An
engine with a little running time has worked out all its initial
stress relief.

Would the use of 150 octane have automatically permitted a higher
ceiling for the machines that used it? Or don't things work quite that
simply! (I understand that specially prepared Spitfires had been able
to fly to at least 44,000 feet by 1943. Would I be right or wrong to
simply assume that 150 octane would have enabled them to go higher?)

No, As with anythig else in Aviation (Or any other Engineering), it's
a balancing act. You can only get so much of a compression ratio out
of a Supercharger, for any given drive speed. In order to get more
boost, you've got to start with thicker air, so the Critical Altitude
actually decreases. When you're chasing V-1s, though, or fighting
against Me 109s, or Fw 190s, that's not a bad thing. The Daimler Benz
engines in the 109, by virtue of their variable-speed blowers, which
didn't require as much power to run at low altitudes, gave a big
advantage down low. The BMW 801 on an Fw 190 had a geared blower, but
the critical altitude for the low gear was very low, down near Sea
Level.
In order to improve altitude performance, you've got to increase the
compression ratio of the induction system, or add an axidizer to the
fuel-air mix to help it burn. This can be done by adding supercharger
stages (Basically one supercharger feeding another, like, say, a
Merlin 60 series engine, or the turbosupercharger/engine driven blower
setups on the P-47 and P-38, or piping something like Nitrous Oxide
into the induction system, as the Germans did. The drawback is that
it takes more of hte engine's power, in the gear-driven examples, to
compress the air that much more. That means that at lower altitudes,
you're at a disadvantage. Or, you've got got to haul around a bunch
of tanks, regulators, pipes, valves, & all that for teh Nitrous
system. You've only got a limited quatity of Nitrous aboard, and you
can pretty much guarantee that it'll run out right when you need it.
Or, worse yet, the storage bottles could get damaged. Leaking
Oxidizers is a Bad Thing, especially when somebody's shooting at you.

More later, with real numbers attached.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

British based Spitfire IX squadrons had converted to 150 octane
(actually 100/150 octane, for lean/rich rating) by, or during, May 44.

Is this the same as 100 octane, then? As used for example in the
Curtiss P-40?

all the best -- Dan Ford
email:

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

In article
thlink.net, Orval Fairbairn
writes
In article ,
Dave Eadsforth wrote:

Good day, good people,

I wondered if anyone out there (in all probability, Peter!) could help
me understand more fully the process by which the Merlin engine was
enabled to use 150 octane fuel; one feature of which was the addition of
the Xylidine anti-knock compound. (This was touched on in a thread
last year, I recall.)

I understand that 150 octane fuel became available during 1944 - I don't
know when (a date would be welcome), but it was available in time to
boost the performance of those Spitfires that were assigned to knocking
down the V1s. What I would like to find out is what might have been
done to the Merlin to allow it to run on the stuff?

Was the use of 150 octane restricted to particular marks of engine?

I read somewhere that it was supposed to provide an effective increase
in power of about 15 percent - by allowing a higher manifold pressure.
Is that figure of 15 percent correct?

Was the conversion to 150 octane done by merely adjusting the existing
arrangements for the supply of fuel, or was there a need for new fuel
supply components (carbs etc.)? And would the permitting of the
additional boost have mandated the exchange of some internal engine
parts (bearings, crankshafts, etc.)?

Would the use of 150 octane have automatically permitted a higher
ceiling for the machines that used it? Or don't things work quite that
simply! (I understand that specially prepared Spitfires had been able
to fly to at least 44,000 feet by 1943. Would I be right or wrong to
simply assume that 150 octane would have enabled them to go higher?)

Thanks in anticipation.

Cheers,

Dave

150 octane means that you can add more boost to the superchargers
without damage to engine components. There MAY ahve been materials
compatability issues with the octane boosters, however.

You can run "rubber" components (seals, hoses, etc.) on petroleum-based
fuels and have no problems; you can run the same components on
naptha-based fuels and have no problems. It is when you switch from one
to the other (either way, BTW) that hoses crack and seals leak.

Thanks for that point.

(It rings a bell - I read that when the US first entered the war,
Britain supplied the Pacific-based USAAF with some aviation fuel that
had originated from a SE Asian oilfield, and it was so differently
formulated that it actually did corrode the seals and hoses.)

Cheers,

Dave

--
Dave Eadsforth

In article , Hildegrin
writes
Dave Eadsforth wrote in message
news:o+F5SWAHQUGAFwMy
...
Good day, good people,

I wondered if anyone out there (in all probability, Peter!) could help
me understand more fully the process by which the Merlin engine was
enabled to use 150 octane fuel; one feature of which was the addition of
the Xylidine anti-knock compound. (This was touched on in a thread
last year, I recall.)

SNIP of incredibly useful amount of historical data.

Thanks very much for taking the time to type in all that information -
very much appreciated.

Re. your pondering about whether the Griffon engine was boosted over 25
in. Years ago, I was invited to take a look inside a Shackleton, and
while in the cockpit I noted that the boost gauges went up to something
phenomenal - I cannot now remember what the numbers were, but they were
definitely well in excess of 25. I did take a photo of the interior and
I will now try to look it out and see if the numbers are readable.

Someone out there who knows more about Shacks might be able to give an
accurate figure.

Thanks again,

Dave

--
Dave Eadsforth

In article , Peter Stickney
writes
In article ,
Dave Eadsforth writes:


Good day, good people,

I wondered if anyone out there (in all probability, Peter!) could help
me understand more fully the process by which the Merlin engine was
enabled to use 150 octane fuel; one feature of which was the addition of
the Xylidine anti-knock compound. (This was touched on in a thread
last year, I recall.)

If you can wait, I've got to dig out some files & make sure of some
references, but I'll have a comprehensive answer in about a day's
time. In the meantime, I'll chuck out a tidbit or two.

SNIP of much appreciated theoretical and practical stuff


Thanks, Peter; that summary has given me a pretty firm grasp of the
essentials for boosting engines. If you do have any additional material
that would be great.

I have recently seen some stuff on the lengths that the Germans went to
to get the Ju86 to fly at high altitude. I had not realised previously
that nitrous oxide could be used with a diesel engine - but the Ju86P
did for its (1,000 HP) Jumo 207B-3s.

Re. diesel engines and the energy it takes to supercharge; that would
explain the planned construction of the Ju86R-3, not just with more
powerful engines (1500 HP Jumo 208s) but also installing the two stage
blower for these within the Ju86 fuselage and driving it with a separate
engine - a supercharged DB 605.

I have pondered why it was that the Luftwaffe did not try to boost the
Ju86R-1s and 2s a bit more in early 1944, when they needed to see what
the allies were doing on the south coast of England, and hence could
have used a recce plane that had a good chance of getting home with the
goods. Perhaps the Jumo 207s had already been boosted to the limit...

Cheers,

Dave

--
Dave Eadsforth

Slightly off track - the Germans did not seem to place the same level
of importance on recce that the Brits and USAF did. Me109s could (some
did) carry a camera in the aft fuselage like the recce P51s (F6?). A
lightened waxed Me109F or G would have a very good chance of
completing a recce pass on an in-and-out basis flown at max speed on a
curving descent or in-and-out at naught feet (prop tips above the wave
tips). It appears to me that the 86R was declared a 'clay pigeon' when
the LW found out Spits and Mosquitoes, appropriately modifed, could
get up that high. Why the LW didn't use 'hot-rodded' photofighters is
beyond me. Maybe they swallowed the 'XX' turned spies' reports as
gospel.
Walt BJ

"WaltBJ" wrote in message
om...
Slightly off track - the Germans did not seem to place the same level
of importance on recce that the Brits and USAF did. Me109s could (some
did) carry a camera in the aft fuselage like the recce P51s (F6?). A
lightened waxed Me109F or G would have a very good chance of
completing a recce pass on an in-and-out basis flown at max speed on a
curving descent or in-and-out at naught feet (prop tips above the wave
tips).


The Me-109G-8 recce variant had a camera in the aft fuselage and did
conduct some photo recon missions over the channel area in 1944.

Keith

(Hildegrin) wrote:

Higher octane allows you to use higher boost pressures. It doesn't
create more boost, it just allows you to "overboost" the engine at
lower alts. Thus at rated alt and above, increased octane had no real
effect (it may have reduced power by a tiny amount, because the fuel
has a lower calorifc value, I think).


Yes, this is exactly right...some think that the higher the
Octane Rating the more "powerful" the fuel when actually high
Octane fuel is less 'powerful' that low Octane fuel. You get the
extra power because you can increase the Manifold Air Pressure
(boost) without causing DETONATION. This is the whole reason
behind high octane useage. Heavy detonation will trash an engine
in short order so you must prevent it.

Water injection also results in higher engine power in a slightly
different manner. Without water the fuel controls supply more
fuel than the engine needs, this very rich mixture cools the
charge in the cylinders lowering the pressure and so prevents
detonation. With water, the fuel mixture is automatically leaned
considerably by the 'de-richment valve' therefore producing more
power.
--

-Gord.

Dave Eadsforth wrote in message ...

Thanks very much for taking the time to type in all that information -
very much appreciated.

That's OK. I didn't do anything towards researching the information.
The thanks really belong to the chap who spent a long time trawling
through the PRO for the info in the first place.

Re. your pondering about whether the Griffon engine was boosted over 25
in. Years ago, I was invited to take a look inside a Shackleton, and
while in the cockpit I noted that the boost gauges went up to something
phenomenal - I cannot now remember what the numbers were, but they were
definitely well in excess of 25. I did take a photo of the interior and
I will now try to look it out and see if the numbers are readable.

I'm mainly interested in the Griffon 65, and wether any other models
of Griffon were fitted to the Spitfire XIV during the war, but any
info on Griffons with 150 octane fuel is very helpful.

Cub Driver wrote in message . ..
British based Spitfire IX squadrons had converted to 150 octane
(actually 100/150 octane, for lean/rich rating) by, or during, May 44.

Is this the same as 100 octane, then? As used for example in the
Curtiss P-40?

all the best -- Dan Ford
email:


The common 100 octane fuel had an octane rating of 100/130, which
means 100 in lean mixture, 130 in rich mixture. 150 octane was
actually 100/150. I suppose that means no difference in lean mixture,
but in rich it had a tremendous effect. The Merlin went from 67" to
82", for example (although the USAAF rated them more conservatively,
at 72" iirc)

100/150 wasn't in use until the spring of 1944, although it was being
tested in 1943.