Aces High Bulletin Board
Help and Support Forums => Aces High Bug Reports => Topic started by: rabbidrabbit on February 02, 2005, 10:48:50 PM
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Ok, cruising around in my f4u4 for the first time in a while and I notice that my fuel consumption at full throttle is 657 gph, for a lark, I hit WEP and it drops to 540 GPH. Is this all right?
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Yes thats correct.
Wep involves water injection, whilst the injection is in progress you need to lower the fuel mixture, hence less fuel usage.
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Was chatting about this with someone just recently. The F4u4 wasn't the only plane in our set that used water injection, right? If it's not, can someone tell me which other planes do, because I don't recall any other plane gaining extra flight time when using WEP.
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No, that is not correct. Check out a pilots manual for more information. One is avaliable at http://www.history.navy.mil/branches/hist-ac/f4u-4.pdf Or, use some common sense. Water produces no energy, instead it removes some energy. Methanol was used mixed with water for the most part, but some direct water injection schemes were used.
Why? Mainly to keep temperatures down when putting more fuel into the engine cylinders. You can't get more horsepower (Kilowatts) out of an engine unless you change its compression ratio (efficiency) or add more fuel. Overheating was the main problem when supercharging the WW2 aircraft engines or putting more fuel into them.
Wish I could view all the squirrely flight maneuvers I have filmed over the last two days. I took up a Dora last night and I think it had 15 (or 20) min of WEP.
Regards,
Malta
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what other US planes used water injection?
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Ok so you presumably are not aware that a lot of engines pump in excess gas using the excess to provide some cooling effect ?
Hell they even use water injection in some modded car engines to do the job of the excess fuel thereby allowing a reduction of fuel giving a better optimised mixture ratio for better power.
I should add at max power loads.
Btw you do know water is composed of Hydrogen and oxygen ?
Are they highly combustible ?
Do you really think chucking extra oxygen and hydrogen molecules is not going to make the power output go up ?
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Yes, running a rich fuel/air mixture is always required for maximum power output so you don't burn the exhaust valves. An excessively over rich mixture will provide additional cooling, but will not provide maximum power. The engine power output comes from the rate of fuel burned. You cannot have higher HP without more fuel consumption (unless you change the engine efficiency). War Emergency Power (WEP) is always more than standard Military power, by definition.
Water will not burn in an internal combustion engine. If it could, we could burn water in engines, and there would be no world energy crisis. Also the energy needed to break water into hydrogen and oxygen significantly exceeds the useable energy produced when burning them, or even using them in a fuel cell. Which has always made me wonder who President Bush's advisors were when he endorsed the hydrogen fueled car? Some rockets and the space shuttle use hydrogen and oxygen as fuel, but that is only because it has the highest specific energy (Calories/lb) of any fuel known.
Water (H20) can not be converted into its component gases in an internal combustion engine and will only change phase from liquid to vapor. That phase change energy is what cools the valves, head, and cylinders. The water injection allows extending the operating range of the engine. No additional power comes from water, but pre-detonation and engine damage are reduced with water (or a water/methanol mixture).
Regards,
Malta
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water cools the engine and raises the compression ratio and helps stop detonation ... what happens when you put a cup of water in a cylinder and try to compress it ? it hydraulics ..
Alchohol does the same thing but it will burn at a certian point... its downfall is it takes 3-4 times more to do the same job .
Hydrogen would be the perfect fuel but the energy it takes to extract it outweighs the practical use of it . its also very dangerous .. Remember the hindenburg ?
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Originally posted by 214thCavalier
Btw you do know water is composed of Hydrogen and oxygen ?
Are they highly combustible ? Do you really think chucking extra oxygen and hydrogen molecules is not going to make the power output go up ?
That's why the Fire Dept chucks all that water on fires, they want those extra Oxygen and Hydrogen atoms to add fuel to the fire!
This is a classic quote, I may have to add it to my sig line.
High School Chemistry 100: As atoms of Hydrogen and Oxygen, both are extremely reactive to each other. They "want" to get married and become H2O. All it takes is a spark to turn the Hindenburg into a rain squall. When they join they release a lot of pre-nuptial energy, also known as an exothermic reaction. [Exothermic reaction: Chemical reaction where the energy content of the products is less than that of the reactants; heat is given out from the system.]
Once married, you have to use up a LOT of energy to return them to free Oxygen and Hydrogen.
The exact same thing occurs between Gasoline and Oxygen.
Gasoline consists of C8H18, that is each molecule of Gasoline consists of 8 Carbon and 18 Hydrogen atoms.
The reaction that takes place when gasoline burns: 2C8H18 + 25O2 --> 16CO2 + 18H2O
Note! Gasoline burning creates: Water !!!! ( and CO2) If that darn water would just add it's Oxygen and Hydrogen back to the fire we could have endless energy forever!
So what does adding water to the engine do?
The main function of these systems is to suppress detonation caused by high temperature and pressure developed within the combustion chamber when the effective compression ratio has been taken beyond the auto-ignition point by either a turbo or a supercharger.
For more on water injection see:
http://www.rallycars.com/Cars/WaterInjection.html (http://www.rallycars.com/Cars/WaterInjection.html)
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Originally posted by stantond
No, that is not correct. Check out a pilots manual for more information. One is avaliable at http://www.history.navy.mil/branches/hist-ac/f4u-4.pdf
It is correct and that info can be found in the pilot's manual. What specifically are you referring to in that link that you posted? That's not the pilot manual BTW. I don't see anything in there about this subject.
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Water injection will not raise the compression ratio of the engine. A hot engine vaporizes the fuel and water which provides cooling. The amount of water added must be much less than the amount of fuel, if you want to increase power. Much like adding fuel, adding a small % of the fuel mass in water will not raise an engine's compression ratio.
Adding water injection will allow an engine to operate at a higher boost (MAP) pressure. That will increase power and provide a higher effective compression ratio due to the higher boost pressure. Only under those conditions will water injection be beneficial. Operating the engine at higher MAP without water injection will damage the engine.
At higher MAP, you are forcing more fuel into the engine as well. That must increase fuel consumption. I just realized that link I provided does not have fuel rate information. The pilots manual does have those rates.
Regards,
Malta
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The F4U uses less fuel on Wep. than on Military power. See this chart:
(http://www.zenoswarbirdvideos.com/Images/F4U/F4USEC.GIF)
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I don't understand why you're bringing compression ratio into this. That's a fixed attribute for the engine regardless of what you're spraying into the cylinder.
I think the problem is that you're viewing power output strictly as the product of how much fuel is going into the cylinder rather than how much fuel-air charge is going into the cylinder. That's an important distinction to make in this case.
What's happening with the F4U is that it has to run extremely rich in military to avoid detonation. When ADI is used, the mixture can be leaned significantly. While a greater charge weight is entering the cylinder, fuel makes up a smaller portion of the charge. So the specific fuel consumption is reduced. The F4U is a bit unusual in that the fuel consumption is actually reduced with water injection. Most other planes with water injection will see a power gain with no or minimal increase in fuel consumption but not the big drop like you see in the F4U.
This information is found in the pilots manual and it shows the same effect that you find in the game. I'll try to make a scan of it. This topic surfaces pretty frequently.
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Thanks Mosq, the -4 manual shows the same effect in the engine chart.
Here's an explanation from the -4 manual as to what is going on.
"When the master water injection switch is turned to "ON" and the throttle-operated microswitch is closed, the solenoid shutoff valve on the water regulator is opened and the electric water pump started. Water pressure acts on a diaphragm to close a jet in the carburetor (deriching the mixture) and to reset the auxiliary stage supercharger regulator, permitting higher carburetor inlet pressure in low or high blower, below critical altitude."
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Well, if it's in the manual, then it must be right (or at least I'll agree with it as far as AH goes). The idea to lean out the mixture due to the water injection sounds plausible. Increasing the MAP boost has the effect of increasing the effective compression ratio. For an IC engine the increased compression ratio relates directly to increased efficiency. With increased efficiency, less fuel can be burned for the same horsepower. However, I always understood that more air went through the carburetor which meant more fuel had to as well.
I was never sure whether that was a typo or not in the PM. No other engine (allied or otherwise) shows that characteristic, at least that I have found when using WEP. Allison and Merlin engines don't and I don't believe any of the BMW or Mercedes do either.
I never found that explanation in the pilot’s manual. Thanks for the explanation.
Regards,
Malta
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AIIIEE make an idiotic statement late at night and live to regret it :D
Keep it as long as you wish Mosq i shall not alter the offending *!*>!*! sentence.
I can live with any and all mistakes i make be it on a bbs or face to face.
Now wheres that rope.....
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LOL
It's going away now. I just couldn't help myself.
:aok
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There are some charts that have been posted here that plot power and specific fuel consumption for the DB and/or BMW engines. You can see the same drop in specific fuel consumption when MW50 is used.
Here's an excerpt taken from a 1951 Navy manual on aircraft fuel that explains it some.
"When water or water-alcohol is used for high power operation, the fuel-air ratio is usually reduced from about 0.10, which is normal at high power, to about 0.08 at the instant the water injection is started. By this means the specific fuel consumption plus specific water consumption will be of the order of 0.70 pound per brake horsepower hour, which is no greater than the specific fuel consumption at the maximum power permissible without water injection."
Here's a better explanation from Vee's for Victory!
"When one views a "carburetor curve" it is apparent that as power is increased to "high power" settings, that the fuel flow is increased proportionally. Much of this fuel is being wasted, for the resulting mixture is "rich"; in fact, all of the oxygen has been burned out of the mixture. This extra fuel is simply acting as an internal coolant, providing a degree of protection against detonation. It can be considered as a very expensive form of ADI. This is obvious from the extremely poor efficiencies shown by engines running at takeoff power, particularly those that are air-cooled.
"Since ADI fluid replaced the need to use fuel as an internal coolant, there is an immediate improvement in the efficiency as measured by fuel consumption. Of couse ADI fluid is consumed in the process, and it has to be carried aloft as well, but there is a considerable difference in cost and engine performance. As a result of the need to reduce fuel flow when using ADI, manufacturers provide a "derichment" valve on their carburetors which reduced fuel flow in proportion to the amount of ADI required to produce the desired power."
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Pyro,
ive notices while watching the E6B that GPH will jump around. F4U-4 for example will go from 550 or so then suddenly jump to 660 or so for sec or 2 then back down to normal. it just spikes to a higher GPH.
Whels
Originally posted by Pyro
There are some charts that have been posted here that plot power and specific fuel consumption for the DB and/or BMW engines. You can see the same drop in specific fuel consumption when MW50 is used.
Here's an excerpt taken from a 1951 Navy manual on aircraft fuel that explains it some.
"When water or water-alcohol is used for high power operation, the fuel-air ratio is usually reduced from about 0.10, which is normal at high power, to about 0.08 at the instant the water injection is started. By this means the specific fuel consumption plus specific water consumption will be of the order of 0.70 pound per brake horsepower hour, which is no greater than the specific fuel consumption at the maximum power permissible without water injection."
Here's a better explanation from Vee's for Victory!
"When one views a "carburetor curve" it is apparent that as power is increased to "high power" settings, that the fuel flow is increased proportionally. Much of this fuel is being wasted, for the resulting mixture is "rich"; in fact, all of the oxygen has been burned out of the mixture. This extra fuel is simply acting as an internal coolant, providing a degree of protection against detonation. It can be considered as a very expensive form of ADI. This is obvious from the extremely poor efficiencies shown by engines running at takeoff power, particularly those that are air-cooled.
"Since ADI fluid replaced the need to use fuel as an internal coolant, there is an immediate improvement in the efficiency as measured by fuel consumption. Of couse ADI fluid is consumed in the process, and it has to be carried aloft as well, but there is a considerable difference in cost and engine performance. As a result of the need to reduce fuel flow when using ADI, manufacturers provide a "derichment" valve on their carburetors which reduced fuel flow in proportion to the amount of ADI required to produce the desired power."
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its a 2800 right? Do other U.S. birds use the same water injection system?
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From what I have read, the P47 did not have a water injection system. However, the documents I read were not the flight manual. The information was in a similar format though for the P&W R18 double wasp 2000HP engine.
Getting back to water injection....
While I will not disagree about what a book states, or a flight manual for that matter, the whole concept of a supercharger (or forced induction system) is to cram more burnable air/fuel through an engine. The more fuel burned in an engine, the more horsepower produced. A 'rich' air fuel mixture does not have 'excess' fuel which does not burn, but burns at a ratio below the stoichiometric air/fuel ratio. Similarly a lean mixture may burn at, or slightly above, the stoichiometric ratio.
The penalty for burning a rich mixture is in emissions and more fuel burned. There is no reason a rich fuel mixture cannot be burned at WEP with ADI on. All the fuel entering the engine will be burned but emission tests will show high NOx pollutants. More horsepower will be generated with a rich fuel mixture compared to a lean mixture using water injection during WEP. The more burnable fuel/air mixture you can stuff through the engine, the more power produced.
I have not thoroughly researched this, but my opinion is that the engine manufacturers were concerned too much horsepower could be produced. I believe a horsepower limit was placed on engines during design or testing which led to the leaning of the mixture during WEP/ADI to keep the horsepower from exceeding 2250 (in the case of the F4U). These were state of the art engines and breaking them during combat using WEP was not an option.
Regards,
Malta
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Water injection increased power for about 15 seconds. when the water is introduced to a hot cylinder, it turns to steam. This causes a momentary increase in compression and when you increase compression you get more power. Once the cylinder has cooled, however, the water no longer converts to steam, the compression benefit is lost. Water injection was useful in cooling the aircooled engine at full load conditions. It was retained in WWII aircraft for that purpose. Another benefit of dumping cold water into a hot cylinder was to clear out carbon deposits, making more room for air/fuel. The P-47s had water injection. The pilots who flew them describe the wonderful boost it got when they flipped the switch but it lasted about 15 seconds. It also made a very hot engine cool very quick. One had to be choosy about when to hit the water.
Refinements to water injection continued through the 50's and many drag racers use it. The advent of Jets and smaller size superchargers made water injection irrelevent by the mid 60s.
NOS does similar things, but it is primarily used to increase compression by taking up Volume. Atleast, that is what my Edlebrock NOS Buddy says. He makes a living at NOS.
Standout, that black cloud coming out of the exhaust is unburned fuel. Black smoke is fuel, white smoke is water and blue smoke is oil. Did you miss that in Automobile repair class?
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Stantond:
I can post a chart if you wish, but there is one fuel/mixture ratio for best power. Increasing or decreasing mixture will both deacrease power. Richen the mixture temps and power go down. Lean the mixture Temp goes up/ power goes down. Lean up to a point when temp again starts droping but power starts droping more rapidly.
HiTech
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Where I grew up, blue exhaust smoke was an indication of excess fuel. Adding water to fuel, just like adding more fuel to a cylinder will not increase the compression ratio. Adding NO (nitrous oxide) to the cylinders is not just adding an inert gas that increases the compression ratio. If that were true, adding argon or nitrogen would work!! Nitrous oxide is an oxidizer, much like potassium nitrate (KN03). It works by allowing all fuel to burn much more efficiently with excess oxygen.
I agree there is an optimal air/fuel ratio for maximum power. As such, I have come to realize that leaning out the air/fuel mixture with water injection (ADI) on provides a maximum power air/fuel mixture. The boost pressure is what controls the maximum power output (at SL) when using ADI. I changed my opinion.
Regards,
Malta
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So, from what I'm seein here,WEP ( on the planes that use water injection) should cool the engine ? Not heat it up ?
O and blue exuast definitly means oil, believe me, I know :)
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Maybe my color descriptions could be better, but when I was a youngster tuning carburettors with an engine vacuum gauge, something resembling blue smoke came from the exhaust when the mixture was too rich. If your car is burning oil, there is a distinct odor with the smoke but the color can be anywhere from blue to grey. Every engine I have been around that burned oil had exhaust smoke that smelled of burnt oil. Black smoke is a sign of excessive fuel or flooding. I suppose one could put that in the 'extra rich' category. These days its not too easy to get a 'rich' air/fuel mixture in a modern engine.
If you followed the discussion, running the engine with the most efficient fuel/air mixture will generate more heat than a 'rich' mixture. The ADI system is just that, Anti-Detonation Injection (ADI), and provides a small amount of cooling. A 'rich' air/fuel mixture cools part of the intake system and reduces pre-detonation. The ADI system operates similarly with water instead of excess fuel. The biggest change in the engine is from raising the boost pressure, which is what generates the extra heat. Intake and exhaust temperatures are raised with higher boost pressures.
Regards,
Malta
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One is avaliable at http://www.history.navy.mil/branches/hist-ac/f4u-4.pdf
One thing I noticed in the above document and I have reaad in other documents is that the F4U-4 as modeled in AH is about 1500 fpm short of what it should do with wep on. 4800 fpm. Is there some reason for this or am I off base?
Thanks Cris
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Interesting document Crispy. Did you notice on he last page "10 min. WEP" .
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Originally posted by MOSQ
Interesting document Crispy. Did you notice on he last page "10 min. WEP" .
That was a quote from above in the list, it was not mine, i must have messed it up quoting it. But yes I noticed that also.