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#51
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Hi Gord,
Yep...very good Friedrich...that's exactly as I see it...one point, you use the term 'preignition' and although I see how you meant it now (and you're correct) I never use that term unless I'm describing the occurance of spark, it can be confused with that.. possibly my mistake - I'm not a native English speaker. What you described to me would have been "ignition advance" - the crank angle before TDC when the spark occurs. What term would you use for occurence of ignition before flamefront or before spark? "Detonation will be evidenced by a rapid rise in cylinder head temp, a rapid rise in oil temp, a rapid drop in torque closely followed by structural parts of the engine emitting from the exhaust stacks" LOL! (not that it's funny when it happens to you in flight...) I think they used that to scare the snot outta us engineers (it worked too!) Not so much on us automotive engineers today... A lot of modern automotive engines are run right along the knock limit for efficiency, with knock control constantly operating. To do this, there has to be a knock event every now and then for the knock control to be able to detect the limit. (Knock control just detects knock events and retards the ignition. When there is no knock, ignition is advanced again until the next knock occurs.) This normally works fine. However on some (not all) engine types, on high load testbed runs this has recently led to very rare statistical occurence of "super-knock" events, with disastrous results. I will be interested to see, how the proposed GAMI PRISM system is going to work in this respect. As far as I understand it, the knock detection principle is much more advanced than what you can afford on an automotive engine (something about continuously measuring the cylinder pressure), but there still has to be the occasional knock for the system to know where the limit is. regards, Friedrich -- for personal email please remove "entfernen" from my adress |
#52
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"Thomas Schoene" wrote in message thlink.net...
R. David Steele wrote: On 14 Apr 2004 22:44:09 -0700, (KDR) wrote: If necessary, is it possible to use F-76 as aviation fuel? I've read somewhere that the RN's Invincible class carrier can trade off her endurance for embarked air group's endurance by using ship fuel tanks as 'swing tanks'. Can anyone confirm this one way or the other? Thanks in advance Do a little research. I suggest the same for you, especialy before you dismiss a reasonable question from a regualr, and usually well-informed, poster. 1) Ship power plants are not "jet engines" -- they are marine gas turbines. Sometimes these are derived from aircraft jet engines, but they are not the same. Terminology matters. 2) Marine gas turbines can burn fuels, like F76 diesel, that are not considered suitable for aircraft engines. They can also burn jet fuel, but the reverse is not true. A jet aircraft probably cannot burn F76, at least not for very long. So I'd agree with several earlier posts that this "swing" tankage would be jet fuel diverted to ship propulsion if need be, rather than F76 diverted to aircraft use. Most modern destroyers and cruisers are powered by jet engines. The Ticonderoga ( CG-47) class and the Spruance class (DD-963) plus new DD-X series (DD-21) are jet powered (four engines to two shafts). The Perry class frigate had two engines. They have not announced how many engines DD(X) will use, but they have said that it will probably be Rolls Royce MT-30s, not the GE LM2500s used in other USN ships. DD(X)'s arrangements may be substantially different from the other ships, since all-electric propulsion means that none of the engines will be coupled directly to a propellor shaft. Originally they were the same engines as used by the L1011 (2500). Nope. The L-1011 used the Rolls Royce RB211. I don't know if this has a direct marine derivative. I suppose the MT30/Trent could be regarded as the great-great great grand-daughter of the RB211-22B on the Tristar David The GE LM2500 is derived from the TF39 (military) and CF6 (commercial) engin es. These are used in the C-5 as well as the DC-10 and many other airliners, but not the L-1011. |
#53
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#54
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#55
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"Friedrich Ostertag" wrote:
Hi Gord, Yep...very good Friedrich...that's exactly as I see it...one point, you use the term 'preignition' and although I see how you meant it now (and you're correct) I never use that term unless I'm describing the occurance of spark, it can be confused with that.. possibly my mistake - I'm not a native English speaker. What you described to me would have been "ignition advance" - the crank angle before TDC when the spark occurs. What term would you use for occurence of ignition before flamefront or before spark? Well, basically the term "preignition" I'd use to describe some event 'prior to ignition' (or the 'time' of normal ignition - spark), so if the mixture was ignited by a hot-spot somewhere in the cylinder then that's 'preignition' (a verb referring to the fact that it occurred prior to 'the time of ignition'. (a noun) English is weird sometimes, I don't think you can refer to preignition (as a verb) when describing any ignition event so I usually refer to it as a noun (the time that the spark occurs - or should occur) "Detonation will be evidenced by a rapid rise in cylinder head temp, a rapid rise in oil temp, a rapid drop in torque closely followed by structural parts of the engine emitting from the exhaust stacks" LOL! (not that it's funny when it happens to you in flight...) I think they used that to scare the snot outta us engineers (it worked too!) Not so much on us automotive engineers today... A lot of modern automotive engines are run right along the knock limit for efficiency, with knock control constantly operating. To do this, there has to be a knock event every now and then for the knock control to be able to detect the limit. (Knock control just detects knock events and retards the ignition. When there is no knock, ignition is advanced again until the next knock occurs.) This normally works fine. However on some (not all) engine types, on high load testbed runs this has recently led to very rare statistical occurence of "super-knock" events, with disastrous results. Yes, that's quite interesting to me, and it backs my opinion of using low test fuel in my cars...I never use high test fuel at all, mind you, I only use standard domestic vehicles but I consider high test wasteful in modern engines with 'knock control'. I will be interested to see, how the proposed GAMI PRISM system is going to work in this respect. As far as I understand it, the knock detection principle is much more advanced than what you can afford on an automotive engine (something about continuously measuring the cylinder pressure), but there still has to be the occasional knock for the system to know where the limit is. regards, Friedrich Yes, I understand that, another good system that GAMI is looking at is their accurate fuel injectors to enable automobile engines to be run lean. We run (perhaps ran might be more accurate) large recip aircraft engines at '10% lean from best power' (by manually leaning them during cruise) for many thousands of hours and they worked fine in that condition, matter of fact they'll continue to run fine as much as about 30% lean before they get unstable, they seem to love lean mixtures!... -- -Gord. |
#56
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Stephen Harding wrote:
wrote: of Keflavik. On reducing power from wet power (full) to METO (climb) I noticed that number 3 engine's torque was about 20 pounds high (other engines were at ~140 pounds), by the time I looked at the fuel flows and noticed that number 3 was much lower than the others that engine started popping and banging and the torque started to fall off rapidly. We punched it out and continued climbing. Seeing as how the weather was fine all over we continued to Summerside. You had some sort of torque meter to watch? I wasn't aware such an instrument was used on aircraft, or actually anything off of a dyno. SMH Oh yes Stephen, it's just about the main engine instrument, very handy indeed...most large recips and even some turboprop a/c use them...the C-130, P-3 Orion, Convair 580 to name a few, on these three the torque gauges are called "Horse Power' but they actually measure the amount of torque applied to the prop-shaft by the engine. -- -Gord. |
#57
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We run (perhaps ran might be more accurate) large recip aircraft engines at
'10% lean from best power' (by manually leaning them during cruise) for many thousands of hours and they worked fine in that condition, matter of fact they'll continue to run fine as much as about 30% lean before they get unstable, they seem to love lean mixtures!.. Been there. Done that (R3350s). One problem is that the power curve is quite steep on the lean side -- pilot has to be more careful. Never did it but have been told if one can see the exhaust stacks, it is easier at night. One leans until one gets the shape/color of exhaust flame that is "correct." Beyond me. Quent |
#58
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#59
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#60
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KDR wrote:
Many thanks for all the replies. Compared with F-76, how expensive is JP-5? http://www.sd.fisc.navy.mil/FUEL/FUEL-INFOR-PAGE.HTML JP-5 $1.03/gallon DFM $0.98/gallon (DFM is Diesel fuel, Marine, another term for F-76) That's roughly 5% difference. It may not seem like much, but considering the Navy's overall fuels budget, it can really add up. Is there any official move in the RN or USN to adopt JP-5 as a single universal fuel? Not that I've ever heard of. -- Tom Schoene Replace "invalid" with "net" to e-mail "Our country, right or wrong. When right, to be kept right, when wrong to be put right." - Senator Carl Schurz, 1872 |
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