100-octane fuel in the RAF in 1940

[Shortround6]

MK II was a more powerful but slightly different plane, on most metrics of speed at altitude it appeared to be worse than the Mk I, but this was because it was optimised to perform better overall, which it did.

The Mk IIs were a bit heavier but the weight hides a few things, like the IFF gear which required an Antenna on each side of the plane

Gear weighed about 40lbs and the extra drag slowed the plane by about 2mph (?)
Armored windscreen, rear view mirror?
The MK II did have a bit more service ceiling than the MK I despite the extra weight.

I am making a guess that the supercharger may have been mispatched between the intake and the gear ratio? The intake of the supercharger may not have allowed the flow desired using the higher rpm of the impeller. They might have gotten the desired pressure but if the supercharger was operating at lower efficiency and heating the intake charge more they might not have gotten the corresponding increase in power?

 

[pbehn]

The Mk IIs were a bit heavier but the weight hides a few things, like the IFF gear which required an Antenna on each side of the plane
View attachment 738086
Gear weighed about 40lbs and the extra drag slowed the plane by about 2mph (?)
Armored windscreen, rear view mirror?
The MK II did have a bit more service ceiling than the MK I despite the extra weight.

I am making a guess that the supercharger may have been mispatched between the intake and the gear ratio? The intake of the supercharger may not have allowed the flow desired using the higher rpm of the impeller. They might have gotten the desired pressure but if the supercharger was operating at lower efficiency and heating the intake charge more they might not have gotten the corresponding increase in power?

These are all part of my general point, the radios and antenna may have ben detrimental to aircraft performance in speed but not as fighting plane. As I understand it the prop on the MKII gave an improvement across the whole range of altitudes in climb and speed. Things like drag on antenna were accepted while every effort was made to produce better (drag free) antenna.

 

[Mike Williams]

The Mk IIs were a bit heavier but the weight hides a few things, like the IFF gear which required an Antenna on each side of the plane
View attachment 738086
Gear weighed about 40lbs and the extra drag slowed the plane by about 2mph (?)
Armored windscreen, rear view mirror?
The MK II did have a bit more service ceiling than the MK I despite the extra weight.

I am making a guess that the supercharger may have been mispatched between the intake and the gear ratio? The intake of the supercharger may not have allowed the flow desired using the higher rpm of the impeller. They might have gotten the desired pressure but if the supercharger was operating at lower efficiency and heating the intake charge more they might not have gotten the corresponding increase in power?

That photo is a 92 Squadron Spitfire VB.

ROYAL AIR FORCE 1939-1945: FIGHTER COMMAND

The Prime Minister of New Zealand, the Rt Hon Peter Frazer, climbs from the cockpit of a No 92 Squadron Spitfire VB at Biggin Hill on the evening of 11 July 1941, during his whistle-stop tour of South Eastern Command.

www.iwm.org.uk

This is a Spitfire II of 19 Squadron at Fowlmere in September 1940. It's new and clean.

Check out the 100 octane fuel bowser!

The Spitfire II pilots thought it was good at altitude, for example Combat Report - F/Lt. J. C. Mungo-Park, 74 Squadron, 30 November 1940 . (Shared with H. M. Stephen. Uffz. Fritz Wägelein, 5./JG 53. BF 109 E-4 Wk Nr 1145. shot down and wounded. )

 

[RCAFson]

The Mk IIs were a bit heavier but the weight hides a few things, like the IFF gear which required an Antenna on each side of the plane
View attachment 738086
Gear weighed about 40lbs and the extra drag slowed the plane by about 2mph (?)
Armored windscreen, rear view mirror?
The MK II did have a bit more service ceiling than the MK I despite the extra weight.

I am making a guess that the supercharger may have been mispatched between the intake and the gear ratio? The intake of the supercharger may not have allowed the flow desired using the higher rpm of the impeller. They might have gotten the desired pressure but if the supercharger was operating at lower efficiency and heating the intake charge more they might not have gotten the corresponding increase in power?

The Merlin XII had the same gear ratio and impeller size as the Merlin 45 but it had the older Supercharger inlet design and produced less power than the 45, even at the same boost pressure:

TO: 12.5/12lb boost, 3000rpm = 1175/1230hp (XII/45). ( British Piston Aero-engines and their aircraft)

The same source lists the Merin XII 87/100 octane permissible boost as TO; 7/12.5lb, climb; 7/9lb at 2850rpm.

 

[Engineman]

The Merlin XII had the same gear ratio and impeller size as the Merlin 45 but it had the older Supercharger inlet design and produced less power than the 45, even at the same boost pressure:

TO: 12.5/12lb boost, 3000rpm = 1175/1230hp (XII/45). ( British Piston Aero-engines and their aircraft)

The same source lists the Merin XII 87/100 octane permissible boost as TO; 7/12.5lb, climb; 7/9lb at 2850rpm.

Yes, this is correct but, perhaps the timeline, context and some of the detail should be carefully considered.
Rolls Royce had wanted to improve the initial Merlin performance but, they had to spend considerable effort to resolve early problems such as the Ramp head total failure.
The Merlin XII introduced the best/fastest improvements that could be achieved in the time available for running with 100 Octane fuel, 70/30 Water glycol cooling and some Supercharger changes that improved performance within the basic original Merlin III design. As such, these were all welcome engine improvements that were available by 1939. However, the use of the Merlin XII came with the introduction of the Spitfire Mk II, which began to see service in August 1940.
Further improvements of the Single-stage fighter Merlin engine were achieved with the Merlin 45. This engine incorporated the considerable changes that included redesign of the supercharger intake and entry airflow. The Merlin 45 really started the full exploitation of the advantages offered by 100 Octane fuel and the suitable design of the engine and supercharger to capitalise on these aspects.
The comparison of 1175/1230hp (XII/45) is only the T/O rating, the Merlin 45 gave much more power than the Merlin XII at altitude, with a rating of 1280hp, +12, 18,000' Rated Altitude.
There is another reason that the Merlin 45 gave a better power output, but this has not been mentioned yet.

Eng

 

[z42]

This account comes to mind - P/O Roger Hall, No. 152 Squadron, 4 September 1940, (Roger Hall D.F.C. Clouds of Fear, (Hodder and Stoughton, London, 1977), pp. 85-86.)

"We were traveling at full throttle and climbing at nearly three thousand feet a minute in the general direction of the enemy formation, which was just visible high up above
View attachment 738006

p.s. great work with the graph!

Why the black smoke at maximum boost? Were they running so rich that there was plenty of incomplete combustion?

 

[Shortround6]

Why the black smoke at maximum boost? Were they running so rich that there was plenty of incomplete combustion?

Basically yes.

Running rich gave several benefits.
1 was the change in knock sensitivity.(change in octane rating).
2 was the extra cooling of the intake charge (which helped counter act the increase in temperature due to higher compression in the supercharger).
3 was the added cooling in general. Some engines were using 30-50% more fuel than they needed for combustion per HP at lean cruise.
Most (or all?) engines that used water injection actual cut the fuel flow through the carburetor when water injection was selected.

 

[bf109xxl]

Basically yes.

Running rich gave several benefits.
1 was the change in knock sensitivity.(change in octane rating).
2 was the extra cooling of the intake charge (which helped counter act the increase in temperature due to higher compression in the supercharger).
3 was the added cooling in general. Some engines were using 30-50% more fuel than they needed for combustion per HP at lean cruise.
Most (or all?) engines that used water injection actual cut the fuel flow through the carburetor when water injection was selected.

From the report "THE PERFORMANCE OF A SUPERCHARGED AERO ENGINE" by Stanley Hooker, Harry Reed and Alan Yarker,
March, 1941:

 

[Daggerr]

Reviews look promising but you`re doing better than me if you can actually find one anywhere in any format for sale (found ONE 2nd hand in Australia so far...)

I don't have that book, but judging from its TOC it might be less interesting than the title implies:

Taken from: 100-octane (ebook), Peter Varey | 9780953844043 | Boeken | bol.com

 

[bf109xxl]

I don't have that book, but judging from its TOC it might be less interesting than the title implies:

View attachment 738152
Taken from: 100-octane (ebook), Peter Varey | 9780953844043 | Boeken | bol.com

Thx for the ToC! Now I see that it should be even more interesting to me than I expected! I would like to evaluate the contributions of key persons/institutions/corporations to the development of technological processes for the production of high-octane gasoline.

 

[Mike Williams]

This table seems to show that while the Merlin XII had greater HP than a Merlin II, there was little change in top speed. Admittedly, all the prop types confuse things. Based on that alone, without an understanding of the larger flight envelope, one could think that 100 octane's benefit was marginal. That would be a mistake as demonstrated here already.

 

[Geoffrey Sinclair]

Note fuel weights may be for different octane ratings. What the RAF says.

Name	Spitfire I	Spitfire II	Spitfire V
Number	1​	1​	1​
Engine Make	Merlin III	Merlin XII	Merlin XLV
Engine Cooling	Liquid	Liquid	Liquid
Horse Power	1,030​	1,150​	1,210​
Power At Height (feet)	16,250​	14,500​	18,250​
Span (feet, inches)	36' 10"	36' 10"	36' 10"
Length (feet, inches)	30'	30'	30'
Height (feet, inches)	10'	10'	10'
Wing Area (square feet)	220​	220​	220​
Crew	1​	1​	1​
Armament Forward Wings	8x0.303"	8x0.303"	4x20mm, 4x0.303"
Rounds Per Machine Gun	350​	350​	350​
Rounds Per Cannon	0​	0​	60​
Weight Tare (pounds)	4,795​	4,738​	n/a
Normal Weight (pounds)	6,255​	6,238​	6,460​
Take Off (Over 50 ft) (Yards)	400​	400​	400​
Landing (Over 50 ft) (Yards)	590​	590​	610​
Climb to Height (feet)	15,000​	15,000​	15,000​
Climb to Height Time (Mins)	6.2​	4.9​	5​
Service Ceiling (Feet)	34,000​	36,800​	37,700​
Maximum Speed (m.p.h)	355​	363​	375​
Max Speed Height (Feet)	19,000​	17,000​	20,250​
Cruising Speed (m.p.h)	304​	314​	310​
Cruise Speed Height	15,000​	15,000​	15,000​
15 Minutes allowance Range (miles)	415​	335​	335​
15 Minutes allowance Endurance Hours	1.4​	1.07​	1.08​
Fuel (for range, pounds)	484​	414​	389​
Fuel (for allowance, pounds)	146​	191​	216​
Fuel (Total, pounds)	630​	605​	605​
Fuel (Total, Gallons)	84​	84​	84​
Miles per 100 pounds fuel	85.8​	80.9​	86​
Maximum Fuel (Economical) Speed (m.p.h)	180 - 190	180 - 190	180 - 190
Height (feet)	15,000​	15,000​	15,000​
Range (15 mins allow.) (miles)	575​	530​	480​
Endurance (15 mins allow.) Hrs	3.1​	2.86​	2.6​
Fuel (for range, pounds)	484​	414​	389​
Fuel (for allowance, pounds)	146​	191​	216​
Fuel (Total, pounds)	630​	605​	605​
Fuel (Total, Gallons)	84​	84​	84​
Miles per 100 pounds of fuel	118.8​	128​	123​

 

[Engineman]

Very interesting posts #91 and #92. The reported power outputs and Rated altitudes would hardly support many of those comparative figures. With anonymous attribution, I think it would be difficult to see the supposed 15% difference in declared power outputs, never mind the prop differences. Nonetheless, I expect that the declared power and Rated altitude
improvements of the Merlin XII (and the Merlin 45/XLV) were tangible. In the real world of WW2 gun combat, a 5mph speed advantage is actually a factor worth having!

Eng

 

[Snowygrouch]

Very interesting posts #91 and #92. The reported power outputs and Rated altitudes would hardly support many of those comparative figures. With anonymous attribution, I think it would be difficult to see the supposed 15% difference in declared power outputs, never mind the prop differences. Nonetheless, I expect that the declared power and Rated altitude
improvements of the Merlin XII (and the Merlin 45/XLV) were tangible. In the real world of WW2 gun combat, a 5mph speed advantage is actually a factor worth having!

Eng

I don't think the values in the tables above include emergency +12lbs rating, I think they`re all the ratings capped at 9lbs.

 

[Snowygrouch]

 

[Engineman]

I don't think the values in the tables above include emergency +12lbs rating, I think they`re all the ratings capped at 9lbs.

Yes, I think so for the Merlin XII max level speed/alt.

Eng

 

[Shortround6]

The comparison of 1175/1230hp (XII/45) is only the T/O rating, the Merlin 45 gave much more power than the Merlin XII at altitude, with a rating of 1280hp, +12, 18,000' Rated Altitude.
There is another reason that the Merlin 45 gave a better power output, but this has not been mentioned yet.

As noted by Engineman, take-off rating is not a good way to compare engines, even engines of the same basic type.
Single stage/single speed Merlin's are particularly troublesome in this regard.
NONE of them were running at wide open throttle at take-off. Take off rating was what they thought they could get away given the fuel being used, the degree of boost supplied by the supercharger and the amount of heat the supercharger was generating in take-off conditions. The throttles were closed off to different degrees to limit the boost to safe levels but this introduced pumping losses.

Great example of this is the Merlin X engine. Same supercharger as the Merlin III but the low gear of the 2 speed drive was 6.389 and that allowed the supercharger to hit 10lbs of boost at sea level. Which was good for 1280hp once they allowed the higher boost.
It also allowed the engine to be advertised at 1065hp at 2850rpm for take-off in 1938 using 87 octane fuel instead of the 880hp at 3000rpm that the Merlin III offered. Wide open throttle on the Merlin X was at 5250ft and gave 1145hp. That is the difference the change in gear ratio (speed of the impeller) makes.


Using the HP of the engine to speed of the airplane only works if you have the same altitudes. The chart/s provided by Mr Sinclair and Mr. Calum show this rather well.
The Spitfire was rather low drag and was able to generate 2-3000ft worth of RAM in forward flight (Hurricanes generated slightly less).

Plane.........Speed...............altitude no RAM..................altitude with RAM................. difference
III.............355mph..................162500ft..............................19,000ft.........................................2750ft
XII...........363mph...................14,500ft...............................17,000ft........................................2500ft
V.............375mph...................18,250ft...............................20,250ft.....................................2000ft

Now we have the fact that the drag drops at about 2% (roughly) per 1000ft of altitude so the XII is fighting about 4% more drag than the III and the V is fighting about 2% less than the III?

This test

Spitfire Mk VA X.4922 Report

shows that a 375mph MK V was good for just under 363mph at 17,000ft and was good for about 368mph at 19,000ft. using 9lbs of boost and these planes were supercharger limited at these altitudes, NOT FUEL limited. That is to say that while 100 octane allowed them to use 9lbs of boost it was the Superchargers of the XII and 45 Merlins that were limited power and speed in the high teens and so do not show the advantage of the 100 octane fuel.
The Fuel allowed for 12lbs of boost in 1940 but the superchargers would not deliver the boost at the higher altitudes.

I would note that many books about the BoB give the wrong reason for the Bf 109s performance at higher altitudes. The DB601A engines did not make more power at high altitudes. The 109 was lighter in weight.

Some of the combat reports on Mr. Williams website show Hurricanes catching 109s at low altitude while using 12lbs of boost so it is rather obvious that the 100 octane fuel did contribute even if it wasn't at high altitude.

 

[Snowygrouch]

As noted by Engineman, take-off rating is not a good way to compare engines, even engines of the same basic type.
Single stage/single speed Merlin's are particularly troublesome in this regard.
NONE of them were running at wide open throttle at take-off. Take off rating was what they thought they could get away given the fuel being used, the degree of boost supplied by the supercharger and the amount of heat the supercharger was generating in take-off conditions. The throttles were closed off to different degrees to limit the boost to safe levels but this introduced pumping losses.

Great example of this is the Merlin X engine. Same supercharger as the Merlin III but the low gear of the 2 speed drive was 6.389 and that allowed the supercharger to hit 10lbs of boost at sea level. Which was good for 1280hp once they allowed the higher boost.
It also allowed the engine to be advertised at 1065hp at 2850rpm for take-off in 1938 using 87 octane fuel instead of the 880hp at 3000rpm that the Merlin III offered. Wide open throttle on the Merlin X was at 5250ft and gave 1145hp. That is the difference the change in gear ratio (speed of the impeller) makes.


Using the HP of the engine to speed of the airplane only works if you have the same altitudes. The chart/s provided by Mr Sinclair and Mr. Calum show this rather well.
The Spitfire was rather low drag and was able to generate 2-3000ft worth of RAM in forward flight (Hurricanes generated slightly less).

Plane.........Speed...............altitude no RAM..................altitude with RAM................. difference
III.............355mph..................162500ft..............................19,000ft.........................................2750ft
XII...........363mph...................14,500ft...............................17,000ft........................................2500ft
V.............375mph...................18,250ft...............................20,250ft.....................................2000ft

Now we have the fact that the drag drops at about 2% (roughly) per 1000ft of altitude so the XII is fighting about 4% more drag than the III and the V is fighting about 2% less than the III?

This test

Spitfire Mk VA X.4922 Report

shows that a 375mph MK V was good for just under 363mph at 17,000ft and was good for about 368mph at 19,000ft. using 9lbs of boost and these planes were supercharger limited at these altitudes, NOT FUEL limited. That is to say that while 100 octane allowed them to use 9lbs of boost it was the Superchargers of the XII and 45 Merlins that were limited power and speed in the high teens and so do not show the advantage of the 100 octane fuel.
The Fuel allowed for 12lbs of boost in 1940 but the superchargers would not deliver the boost at the higher altitudes.

I would note that many books about the BoB give the wrong reason for the Bf 109s performance at higher altitudes. The DB601A engines did not make more power at high altitudes. The 109 was lighter in weight.

Some of the combat reports on Mr. Williams website show Hurricanes catching 109s at low altitude while using 12lbs of boost so it is rather obvious that the 100 octane fuel did contribute even if it wasn't at high altitude.

The light weight of the 109 helps its cause, but with respect to service ceiling, it also has a much higher wing loading. I think its likely this negated most of the advantage
of light weight with respect to high altitude flight.

It is a complicated question, but at this time, I believe the early higher performance of the 109 at high altitude vs RAF fighters, was mostly due to the over-estimation of
the output of the Merlin at high altitudes, rather than any magic tricks on the German side, which of course meant that things like the Spitfire didn't quite perform as expected. The DB601 has an easier job performing at its rated output at higher altitude as its running lower boost pressure.

In Germany they made far more use of very advanced high altitude engine test cells, and so tended to get a better idea of what the real performance would be, RR had no altitude test cell at all in 1940, the only one in Britain was at Farnborough and by all accounts it was usually broken or under-sized for the engine in question. This was mainly what Hookers booklet "The Performance of a Supercharged Aero Engine" was about, correcting the primitive and inaccurate basic equations RR had been using to predict what the engine power would be at high altitude.

Anyway... veering off topic a bit here... but note that the speed discrepancy was also partly down to some very bad manufacturing finish, not wholly the
lack of widespread use of high altitude engine test-cells.

 

[Clean32]

Do you know anything about "Sweeney's Blend?

Edit, Fwiw, I found this just now:
The key development came, Dr. Sweeney said, when the researchers achieved "hydrogenation of a special kerosene from Venezuela called quid quiri." In this process, the kerosene was heated, pressurized and treated with hydrogen to obtain a gasoline called a base stock. To the base stock was added alkylate (an exceptionally high‐octane synthetic), tetraethyl lead, aromatic and other high‐octane components.

The resulting fuel, according to Mi. Holt, was "a combination of a number of fuel compounds that had not been made in any great quantities before." Mr. Holt, while not a researcher on the team, kept in touch and contributed advice as one of Standard Oil's top chemical engineers.

The new fuel was called BAM 100, or 100/130 octane, the latter designation because it gave the British aircraft up to 30 percent more horsepower when taking off and climbing than ordinary 100 octane would have given. The British Air Ministry was "tickled to death to get it, Dr. Sweeney noted.

The first tanker load of BAM 100 went to England in June, 1939. In September, 1939, World War II began with the Nazi invasion of Poland. By March of 1940, the R.A.F. was converting the Merlin engines of every Spitfire and Hurricane fighter from 87‐octane gasoline to BAM 100. The Battle of Britain began in July, 1940.​

Who Helped Win Battle of Britain (Published 1978)

William J Sweeney recalls development of high-octane fuel that enabled RAF to defeat Ger Luftwaffe in Battle of Britain; he headed chem engineering team at Standard Oil of NJ, now Exxon, that developed fuel (M)

www.nytimes.com

Nice but not quite correct.
BAM was the USA produced fuel, which was as someone has posted above a lower grade fuel with additives. IE Sweeney's blend

the Venezuela high octane fuel with was as you have posted was a british concern developed fuel, Hydrogenated. this was pre war and this is the fuel used in the Battle of france and the battel of Britain. it was also the fuel used by example the B17 and P51s on long range missions as it didn't build up on the sparkplugs. latter on Standard oil also converted there concerns in Venezuela to produce the same. the result being that 90% of all high octane fuel by the end of the war was coming from this method and this Place

the dutch east indies and Iran both were producing high octane fuel by the acklaine method. but obviously the dutch was lost to the japanese and Iran was busy with north africa and burma.

But it gets even more complicated. Venezuelan crude was shipped to american and dutch refinery's pre war so it's not always clear cut
but when you read that american high octane save BOB which is rubbish. or High octane fuel gave 30% more power, which is borderline true. but thats compared to the normal 80 octane.

But what was the advantage of high octane fuel during the BOB. takeoff and climb to 10 000 feet, after that there was not enough boost/oxygen to take advantage. not until the Mk IX was there enough oxygen to take advantage of the higher octane fuel.

 

[Mike Williams]

More comparison data here:

Comparisons of Spitfire I's with DH and Rotol props and bullet proof windscreen found top speeds to be similar with N.3171 obtaining 354 mph and R.6774, 355 mph. By comparison, Spitfire I K.9793 with a DH two-pitch prop and original windscreen reached 367 mph.

While costing speed, the bullet proof windscreen did prove its worth.