eastwest

Jet fuel was not always a kerosene-like product. The first truly functional jet aircraft was the German ME 262 and it ran on gasoline. However, the decision to move the industry toward a kerosene like product was made for three reasons, safety, space, and cost. Gasoline is more flammable, it has fewer BTU's of energy per gallon, and it's in higher demand for cars -- so kerosene was chosen.

Over the years, many jet fuels have been developed. The best known are the "JP" fuels. They range from JP-4 (little used now) to JP-8. In addition there are some specialty military fuels like JP-10 (used for cruise missiles.)

Jet A and Jet A-1 are the same except for the freeze point.(Freeze point is not the temperature when fuel freezes, as the fuel is warmed from a lower temperature, it is the point where the last apparently frozen fuel melts -- The point when the last crystals of paraffin disappear.)

Jet B and JP-4 are only used in very cold climates where Jet A type fuels will not vaporize well. It is difficult to start an engine if the fuel will not vaporize easily.

JP8 is Jet A1 with three additives: a conductivity improver/static dissipater, corrosion inhibitor, and anti-icing additive.

JP5 is much like Jet A fuels but with a higher flash point (temperature when it vaporizes readily.) This makes it a safer fuel for use aboard ships that fuel aircraft and helicopters. It's not limited to aircraft carriers, there are many smaller ships capable of launching helicopters and Harrier VTOL aircraft. In addition, helicopters are fueled in flight from a variety of ships including destroyers.

Some of the more common additives are:

1. Corrosion inhibitor - used to improve the "lubricity" of the fuel to reduce wear on fuel system components such as pumps and valves.

2. Anti-icing additive - used to prevent condensed water from forming as ice crystals and clogging fuel systems.

3. Biocides - used to kill bioorganisms that grow in stored fuel.

A new additive type is being explored which is designed to allow improvement in the engines. To understand this, you must first understand that fuel breaks down at high temperatures and can clog the injection nozzles. A major requirement in jet engine design is to keep that temperature down, not an easy task since the fuel burns at a very high temperature just as it leaves the injector nozzle. The US Military has had great success with an additive commonly referred to as "+100." This additive permits the fuel to pass the thermal stability test at a temperature 100 degrees Farenheit higher than commercial jet fuel. This margin permits increased engine performance without hazardous deposit accumulation. It is a required additive in the new high performance fighters. Work is underway to explore applications of this technology in commercial aircraft.

bluewatersail

What I wonder about is the smell of jet fuel. When I was a child I can remember getting out of the car at the airport and immediately smelling what I was told was jet fuel. I always associate that smell with travel. I no longer smell that smell. Can you tell us if the odor I associate with jet fuel is natural or is it an additive? Does jet fuel have less of an odor nowadays or have I just gotten used to the smell and therefore don't notice it?

dlombard

Thanks for that post. I always wanted about that stuff. :-)
Someone in the US Army told me that diesel is very similar to jet fuel which is why they're able to put jet fuel into their H1 Hummers. Told me the main difference is the purity is higher in jet fuel than in diesel.

FWAAA

Perhaps your sense of smell has deteriorated with age? Are you a smoker, by chance?

I'm not positive, but it sounds to me that the smell you are describing is not jet fuel itself, but the smell of the exhaust of the jet engines. And I can verify that after many years, it still smells the same to me.

I can still smell jet fuel exhaust near the airport, in the terminals (comes wafting up the jetways) and thru ventilation ducts and often even onboard the airplane itself. And you are right - that smell is the smell of travel.

NickW

My favourite is JP-7 ... a blended fuel which is so inert that you can actually extinguish a cigarette by stubbing it out in a dish of the stuff. In the aircraft which is best known for using the fuel, tetraethyl borane (which detonates violently on exposure to air) is needed to ignite the fuel at engine start or afterburner ignition.

The aircraft in queston is, of course, the SR-71 Senior Crown - better known as the Blackbird.

http://www.well.com/~nickw/sr71.jpg

That one is tail number 64-17951 at the Pima Air Museum in Tucson, AZ.

eastwest

I'm glad that some people found this interesting. The observation was made about Jet Fuel being "the smell of travel." Perhaps that's why I like it so much!

AFAIK, the smell of jet fuel or burning jet fuel hasn't fundamentally changed. I suppose that additives could potentially change it, but the additives really are in small amounts. For example, a 7500 gallon tractor trailer delivering Jet A only has about 10 gallons of anti-icing additive in it. So the percentage of additive is very small.

Diesel fuel is much like Jet A. Many airports use Jet fuel in their diesel powered tugs and ground equipment. It's not totally interchangable, though. Long term use of Jet Fuel in Diesel engines will lead to their early demise.

Another way that Jet is like Diesel is that it's rather oily when compared to regular gasoline (referred to in the aviation industry as "mogas") and aviation gasoline (referred to as "avgas.")

However, it's important to note that chemically, jet fuel is not a variant of diesel, it is a form of kerosene. Diesel has a much higher molecular weight, and most diesel will solidify at temperatures around -4 degrees Fahrenheit.

Dambus

Wow!
Great post ^

cawhite

Thanks eastwest!!!! ^ ^

hhonorman

I love the smell of jet fuel in the morning. It smells like...... vacation.

zaphood

Hi!

Thanks for an interesting post. I have been looking for info on this topic for some time. And I agree it's interesting how strongly the smell sense is connected to memories. That smell brings me into vacation mode still.

I have a question related to this that someone might know better than me;
Why does Jet A1 exhaust smell different coming out of a jet engine than from a piston engine? We have a modified C172 in my flight club that uses a piston diesel engine (much like Dimond aircraft's engines). However the smell of the exhaust is completely different. Is it due to different combustion temperature or something else?

HMO

Nice post, thanks ^

frankmu

Excellent post! Thanks!

Quick question, how did they remove the black exhaust that I use to see from old jets? Modern planes do not seem to leave any exhaust behind them.

cmn.jcs

FYI, diesel fuel isn't jet fuel.

WChou

Diesel does not refer to the type of fuel. Rather, it describes the cycle used. Cessnas with diesel engines are fueled with JET-A and JET-A1.

Steve_in_VA

The standard fuel for U.S. military vehicles with diesel engines is JP-8.