If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
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 |
#2
|
|||
|
|||
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 |
#3
|
|||
|
|||
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 |
#4
|
|||
|
|||
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 |
#5
|
|||
|
|||
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 |
#6
|
|||
|
|||
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 |
#7
|
|||
|
|||
"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 |
#8
|
|||
|
|||
|
#9
|
|||
|
|||
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. |
#10
|
|||
|
|||
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. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
spaceship one | Pianome | Home Built | 169 | June 30th 04 05:47 AM |
Yo! Fuel Tank! | Veeduber | Home Built | 15 | October 25th 03 02:57 AM |
Pumping fuel backwards through an electric fuel pump | Greg Reid | Home Built | 15 | October 7th 03 07:09 PM |
More long-range Spitfires and daylight Bomber Command raids, with added nationalistic abuse (was: #1 Jet of World War II) | The Revolution Will Not Be Televised | Military Aviation | 161 | September 25th 03 07:35 AM |
#1 Jet of World War II | Christopher | Military Aviation | 203 | September 1st 03 03:04 AM |