Author Topic: Is the f4u4's fuel use broke? (Read 2002 times)

rabbidrabbit · « **on:** February 02, 2005, 10:48:50 PM »

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?

214thCavalier · « **Reply #1 on:** February 03, 2005, 07:41:10 AM »

Yes thats correct.
Wep involves water injection, whilst the injection is in progress you need to lower the fuel mixture, hence less fuel usage.

Engine · « **Reply #2 on:** February 03, 2005, 08:56:08 AM »

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.

stantond · « **Reply #3 on:** February 06, 2005, 11:41:38 AM »

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

rabbidrabbit · « **Reply #4 on:** February 06, 2005, 11:44:22 AM »

what other US planes used water injection?

214thCavalier · « **Reply #5 on:** February 06, 2005, 05:12:35 PM »

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 ?

stantond · « **Reply #6 on:** February 06, 2005, 08:07:33 PM »

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

Roscoroo · « **Reply #7 on:** February 07, 2005, 09:59:28 AM »

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 ?

MOSQ · « **Reply #8 on:** February 07, 2005, 11:29:42 AM »

Quote

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

Pyro · « **Reply #9 on:** February 07, 2005, 11:32:22 AM »

Quote

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.

stantond · « **Reply #10 on:** February 07, 2005, 11:46:53 AM »

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

MOSQ · « **Reply #11 on:** February 07, 2005, 01:00:55 PM »

The F4U uses less fuel on Wep. than on Military power. See this chart:

Pyro · « **Reply #12 on:** February 07, 2005, 01:02:05 PM »

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.

Pyro · « **Reply #13 on:** February 07, 2005, 01:09:25 PM »

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."

stantond · « **Reply #14 on:** February 07, 2005, 01:46:23 PM »

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