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mandargb
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Jet Fuel: Why Not Gasoline

Tue Nov 23, 2004 3:54 pm

Hi,
I understand that Jet fuel is mostly kerosene.
Why not Gasoline? Gasoline has higher Calory value that kerosene and hence would generate more power per unit weight.
Thanks in advance.
 
videns
Posts: 132
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Jet Fuel: Why Not Gasoline

Tue Nov 23, 2004 4:04 pm

But it also has higher octane ratings, which makes it more difficult to burn. What you want with car engines, is a sudden and localized fuel "explosion" to move the pistons.
On aircraft engines, you want the fuel to start burning and never end doing so until you tell them to (cutoff the fuel).
Travel? Why would i travel if I can watch it on TV?
 
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HAWK21M
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Jet Fuel: Why Not Gasoline

Tue Nov 23, 2004 4:39 pm

Constant Volume & Constant Pressure Cycled Engines.
 Smile
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
Dalmd88
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Jet Fuel: Why Not Gasoline

Tue Nov 23, 2004 5:07 pm

Jet fuel is cheaper than gasoline. It is also safer to handle.
 
efohdee
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Jet Fuel: Why Not Gasoline

Tue Nov 23, 2004 6:29 pm

In a turbine engine, the fuel is not compressed with the air, so you dont have to have an antiknock value. Piston engines compress the fuel/air mixture, so the fuel has to have resistance to detonating prematurely, antiknock qualities. Jet fuel is also cheaper, and has better lubricating qualities than gasoline.
Also jet fuel conatains 18,500 btu per pound and gasoline about 20,000 btu per pound. But a gallon of jet fuel (6.7lbs) weighs more than a gallon of gasoline (6.0lbs), so jet fuel has more energy content per gallon.
You can use gasoline in a turbine engine, it would just be much more expensive and would wear out the fuel control.
 
CLT18R
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Jet Fuel: Why Not Gasoline

Wed Nov 24, 2004 5:24 am

I would assume the same is true in a diesel engine...disel also being a cousin of Jet-A
 
smcmac32msn
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Jet Fuel: Why Not Gasoline

Wed Nov 24, 2004 11:08 am

Jet fuel is cheaper than gasoline.

I don't ever remember paying $3.29/gallon or more for Gasoline. I pay $1.939 for gas, so I don't know how it can possibly be cheaper than JET-A. JET-B is a mix of kerosene and gasoline that was banned in the US in the 1960's because of the flamibility of it. It caused several lightning related crashes when a plane was hit.
Hey Obama, keep the change! I want my dollar back.
 
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Starlionblue
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Jet Fuel: Why Not Gasoline

Wed Nov 24, 2004 10:57 pm

Jet fuel is cheaper than gasoline.

I don't ever remember paying $3.29/gallon or more for Gasoline. I pay $1.939 for gas, so I don't know how it can possibly be cheaper than JET-A. JET-B is a mix of kerosene and gasoline that was banned in the US in the 1960's because of the flamibility of it. It caused several lightning related crashes when a plane was hit.


Come to Europe where Gas is over $4/gallon  Big grin
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
smcmac32msn
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Jet Fuel: Why Not Gasoline

Thu Nov 25, 2004 3:17 pm

Starlionblue - Yeah, forgot about how bad you guys do have it over there with the gas prices. But of course you have something that is light-years ahead of us with the EuroRail. On-time and efficient. Amtrak is so sparse over here and its needing government subsidy to stay alive. Ofcourse, so is our airline industry. LOL.
Hey Obama, keep the change! I want my dollar back.
 
N867BX
Posts: 295
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Jet Fuel: Why Not Gasoline

Thu Nov 25, 2004 4:08 pm

The number one reason jets burn kerosene.......COST, COST and COST.
Most fuel controls can be adjusted to allow for use of gasoline in a pinch.
 
pilotaydin
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Jet Fuel: Why Not Gasoline

Fri Nov 26, 2004 8:33 am

cant a jet engine be run on tequila...just for a little while  Smile
The only time there is too much fuel onboard, is when you're on fire!
 
kaddyuk
Posts: 3697
Joined: Thu Nov 08, 2001 1:04 am

Jet Fuel: Why Not Gasoline

Fri Nov 26, 2004 11:21 pm

We looked into this in maintainance practices.

One of the more important factors of Kerosene is that it acts as a lubricant, has a higher flash point and burns for longer.

Coupled with the fact that its cleaner, makes for a very efficient way of doing things...

Whoever said "laughter is the best medicine" never had Gonorrhea
 
cloudy
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Jet Fuel: Why Not Gasoline

Sat Nov 27, 2004 12:09 pm

I don't know the technical reasons - but in just about every mobile application where economic efficiency is important, some variant of kerosene is used. Diesel locomotives, diesel ships, commercial trucks, etc. all use kerosene like fuels almost exclusively. Only passenger vehicles and general aviation props mostly use non-kerosene fuels. There are very few large gasoline or avgas engines used for commercial purposes.

The average driver in the United States looks around and sees more gasoline available than diesel but that gives a very false picture. Just about all the commercial freight and passengers in the world, other than stuff going in personal cars or planes, is moved by diesel or jet fuel. Even general aviation is moving in the direction of keroseen, and low-sulpher diesel may make it possible for the diesel car to make a comeback in the US.

Keroseen moves the world. I've heard some ideas as to why this is, but nothing definitive. Perhaps someone more knowledgeable could give us a clue.
 
gigneil
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Jet Fuel: Why Not Gasoline

Sat Nov 27, 2004 2:17 pm

Gasoline has higher Calory value that kerosene and hence would generate more power per unit weight.

Just to reiterate, this is not true if the unit you're talking about is gallons. One gallon of kerosene generates about 140,000 BTUs of energy vs. 125,000 for gasoline.

N
 
srbmod
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Jet Fuel: Why Not Gasoline

Mon Nov 29, 2004 8:09 am

With kerosene being one of the byproducts of oil refining, it just made sense to find other uses for it other than as fuel for heaters and stoves.
 
bhill
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Jet Fuel: Why Not Gasoline

Tue Nov 30, 2004 4:27 am

Prolly not Tequila..but mayhaps Bacardi 151...
Carpe Pices
 
prebennorholm
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Jet Fuel: Why Not Gasoline

Tue Nov 30, 2004 6:28 am

Mandargb: Gasoline has higher Calory value that kerosene and hence would generate more power per unit weight.

Gigneil: Just to reiterate, this is not true if the unit you're talking about is gallons. One gallon of kerosene generates about 140,000 BTUs of energy vs. 125,000 for gasoline.

Both are correct.
Gasoline = more energy per weight unit.
Kerosene = more energy per volume unit.
(Kerosene is considerably heavier than gasoline)
Always keep your number of landings equal to your number of take-offs
 
aviopic
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Jet Fuel: Why Not Gasoline

Tue Nov 30, 2004 6:49 am

In a turbine engine, the fuel is not compressed with the air, so you dont have to have an antiknock value. Piston engines compress the fuel/air mixture, so the fuel has to have resistance to detonating prematurely, antiknock qualities. Jet fuel is also cheaper, and has better lubricating qualities than gasoline.

I agree with the antiknock story but not with the compression part of it.
Without air nothing is going to burn, not even in a turbine and it is not for no reason there is a compressor in every turbine engine.
First the air is compressed then the fuel(of whatever kind) is injected in the burner part of the engine which together is your compressed air fuel mixture like you will find in any other kind of petrol engine.
With one difference though, both diesel and kerosene will ignite by it self when compressed enough and ignited just ones.
After that it is just a matter of keeping the compressed air and fuel going and the burn process will sustain it self.
Oh... and something else..... Kerosene in your diesel car works fine  Smile/happy/getting dizzy

Willem

The truth lives in one’s mind, it doesn’t really exist
 
prebennorholm
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Jet Fuel: Why Not Gasoline

Tue Nov 30, 2004 8:53 am

Right Aviopic, sure the air is compressed in a turbine engine. In a modern high bypass ratio engine the core air at max N2 rpm is in fact compressed up to around 25 times which compares quite well to the compression ratio of a diesel engine.

You may complain that a diesel engine usually only has a compression ratio around 16 or 18. But that doesn't take into account the extra pressure from the heat buildup during the compression stroke.

But the anti knock value of the fuel has no relevance in the turbine since the fuel is burned immediately and graduately as it is injected into the compressed air in the combustion chambers.

That is in fact also identical to the diesel engine on which the fuel is injected into the cylinder after the compression stroke.

On an ordinary gasoline engine it is very different. The air and the fuel is mixed in the carburetor or - in case of most fuel injection systems - injected into the inlet manifold during the inlet stroke and before the compression stroke. Then it is ignited by the spark plug, and one of two things happen:

1. the flame spreads gradually away from the spark plug into the fuel/air mixture - the normal situation.

2. the fuel/air mixture self ignites and burns in one sudden process - that's knocking.

No engine works well with a sudden burn of any extended amount of fuel. In the turbine engine and the diesel engine the burn becomes gradual by the gradual injection into the combustion chamber. In the gasoline engine it becomes gradual by adjusting the compression ratio and fuel properties (octane number) to such values that self ignition does not occur.
Always keep your number of landings equal to your number of take-offs
 
LineMechQX
Posts: 76
Joined: Wed May 12, 2004 6:02 pm

Jet Fuel: Why Not Gasoline

Wed Dec 01, 2004 3:06 pm

Smcmac32msn-
$3.29 a gallon? I'm assuming you've come up with this number as a price of Jet-A. I'm not sure where people are paying this much for fuel. As of Oct, 04 the average price of Jet-A for the airlines in the northwest market was $1.49 and in Oct 03 it was $0.93. I barely remember paying .93 a gallon for unleaded, and I sure wasn't in 2003. In Oct of 04 I was paying over $2 in Portland, so I think I'd rather be buying that Jet-A. When I started in 01 jet-A was around $0.50 a gallon.

Late PC
 
CP744
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Jet Fuel: Why Not Gasoline

Fri Dec 03, 2004 4:12 am

Just to give everyone an idea of fuel costs in CYEG......

Jet-A... Contracted price the last time I saw an invoice... about two weeks ago.... 68.3 cents a litre... approx $2.73 a U.S. gallon $3.10 an Imperial gallon.

Regular gas at the pump 72 to 78 cents a litre.... depends on whether it's a long week-end ;>). Premium up to 88 cents a litre..... $3.52 a U.S. gallon.... $3.99 an Imperial gallon...... I remember paying 55 cents a gallon when I started driving...... I'm not 300 years old...LOL..... Filled up my first car for $5.00.........
 
doug_or
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RE: Jet Fuel: Why Not Gasoline

Mon Dec 06, 2004 2:41 am

the price airlines pay for jet-A is signifcantly diffrent than what the the guy in the Kingair pays @ Signature.
When in doubt, one B pump off
 
wingscrubber
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RE: Jet Fuel: Why Not Gasoline

Wed Dec 08, 2004 12:32 am

Kerosene is used in jet engines primarily for the rate at which it burns - the flame in a jet engine must be stable and continuous, unlike the repeated individual explosions which occur in a reciprocating petrol engine; if the fuel burns too quickly the flame could be extinguised/burn too hot, and if it burns too slowly the engine could flameout. Similar principle to mixing rate with air - too much air and the flame is extinguished, too little and the engine will flame out. This is what I've been spoon-fed for my aero. eng technology exam in january anyhoo.

-Pete
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Venus6971
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RE: Jet Fuel: Why Not Gasoline

Tue Dec 14, 2004 2:37 pm

From my school days I always thought jet fuel was 50/50 mixture of kerosene and gasoline, many of our diesel powered aerospace ground equipment has been rigged to run on our vintage JP-8
I would help you but it is not in the contract
 
Thrust
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RE: Jet Fuel: Why Not Gasoline

Tue Dec 28, 2004 8:38 am

Is kerosene also a lighter fuel than gasoline? Somehow I thought this might be an additional reason for using kerosene as opposed to gasoline  Confused
Fly one thing; Fly it well
 
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Starlionblue
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RE: Jet Fuel: Why Not Gasoline

Tue Dec 28, 2004 9:16 am

Is kerosene also a lighter fuel than gasoline? Somehow I thought this might be an additional reason for using kerosene as opposed to gasoline

I believe so. But this argument is not really that relevant. The specific impulse per weight (how much bang for a certain weight) you get counts. If gasoline weights twice as much but has three times as much specific impulse, you're still (very theoretically) better off.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
MD11Engineer
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RE: Jet Fuel: Why Not Gasoline

Wed Dec 29, 2004 1:08 am

The main reason is:

Kerosene is much cheaper than Avgas. Back in the 1950s, kerosene was actually waste product from the manufacturing of gasoline.

Also, the flame point of kerosene is higher, which makes it less of a fire risk.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
DeltaGuy
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Joined: Wed Sep 12, 2001 5:25 am

RE: Jet Fuel: Why Not Gasoline

Wed Dec 29, 2004 5:08 am

Hey, don't knock Signature, I just got hired by them yesterday as an aircraft refueler, I start Thursday  Big thumbs up So this thread is some very useful gouge now! Big grin

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
prebennorholm
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RE: Jet Fuel: Why Not Gasoline

Wed Dec 29, 2004 10:18 am

Thrust: Is kerosene also a lighter fuel than gasoline?

No. Kerosene is heavier. It is roughly 820 grams/litre while gasoline is some 720 to 735 grams/litre depending on winter- or summer-fomulation. Winter gas is lighter (evaporates at lower temperature) in order to make start of your cold car easier.

But energy is roughly the same per weight unit which means that with kerosene you pack more energy into a smaller tank volume.

Diesel oil is even slightly heavier. We all know that a diesel car has better milage than a gas car. That's partly because diesel is a more compact fuel. You simply buy more energy when you buy a gallon of diesel oil instead of a gallon of gas.

Jet A1 is the perfect fuel for turbine airliners. It almost has all advantages of diesel fuel, and unlike diesel fuel it does not freeze at high altitude.

JP-4 is widely used by military turbine powered planes. It is more like gasoline. JP-4 burns much better in afterburners where the fuel has to burn rather fast at relatively low pressure. That requires a lighter, more gas-like fuel.
Always keep your number of landings equal to your number of take-offs

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