Author Topic: Is the f4u4's fuel use broke? (Read 2001 times)

214thCavalier · « **Reply #15 on:** February 07, 2005, 03:26:07 PM »

AIIIEE make an idiotic statement late at night and live to regret it

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.....

MOSQ · « **Reply #16 on:** February 07, 2005, 04:15:53 PM »

LOL

It's going away now. I just couldn't help myself.

Pyro · « **Reply #17 on:** February 08, 2005, 09:59:36 AM »

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."

whels · « **Reply #18 on:** February 08, 2005, 01:54:30 PM »

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

Quote

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."

rabbidrabbit · « **Reply #19 on:** February 08, 2005, 04:58:30 PM »

its a 2800 right? Do other U.S. birds use the same water injection system?

stantond · « **Reply #20 on:** February 10, 2005, 07:49:51 AM »

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

Stegahorse · « **Reply #21 on:** February 10, 2005, 01:33:34 PM »

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?

hitech · « **Reply #22 on:** February 10, 2005, 02:40:16 PM »

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

stantond · « **Reply #23 on:** February 10, 2005, 07:14:29 PM »

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

Flit · « **Reply #24 on:** February 10, 2005, 08:58:48 PM »

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

stantond · « **Reply #25 on:** February 10, 2005, 11:22:43 PM »

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

Crispy · « **Reply #26 on:** February 11, 2005, 11:28:24 AM »

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

MOSQ · « **Reply #27 on:** February 11, 2005, 11:45:34 AM »

Interesting document Crispy. Did you notice on he last page "10 min. WEP" .

Crispy · « **Reply #28 on:** February 11, 2005, 12:02:16 PM »

Quote

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.