Rather than hijack the Chemtrails thread with a side-discussion about jet fuel, I’m posting here.
New member mugaliens mentioned that jet fuel is basically a mixture of kerosene and gasoline. The things I’ve flown use avgas; and even if I flew turbines, I’d just make sure what’s on the pump matches what’s placarded on the fuel receptacle. mugaliens posted a couple of links, and now my interest is piqued.
The first link capitalises ‘Jet Fuel’, which makes me think that that is their trade name for their product. I know I have seen something called ‘Jet Fuel’ for race cars, that is just high-octane gasoline; but I doubt it’s the same thing as described on the first link. It also mentions ‘turbine power units’ instead of aircraft engines.
The second link says that ‘the first jet fuels were based on kerosene or a gasoline-kerosene mixture’, and ‘the most common jet fuel is a kerosene and paraffin oil-based fuel’. Hm… I thought paraffin was British for ‘kerosene’. Anyway, this link implies that jet fuel is not longer a blend of kerosene and gasoline.
So I looked on Wiki for a lead. The article on JP-4 says it was a 50/50 mixture of kerosene and gasoline; but it was uncited. I followed their footnote to BP’s history of jet fuel, which says JP-4 was a mixture of kerosene and naphtha. Naphtha is used to make high-octane gasoline, but I gather it is not gasoline itself. The BP site says that there was a proposal to create a mixture containing gasoline called Jet Mix, but it was never used operationally.
All I ‘know’ about jet fuel vs. avgas is that if you try to burn jet fuel in a piston-engine aircraft, it’s not going to run (like trying to burn Diesel fuel in your gasoline car’s engine); and that you need to be very careful about burning gasoline in a turbine engine, lest you burn it up with the higher-volatility fuel.
So what’s the straight dope? Does modern jet fuel use gasoline in the mix? If not, when did it stop being used? You there, Una?
The standard jet fuel used in the US is Jet-A, kerosene-based with naphtha and some other hydrocarbons in the mix. Yes, diesel engines will typically run on it, in fact the new generation of aircraft diesels are optimized for it.
The term “jet fuel” is used to describe a variety of similar fuels specifically designed to power jet turbine engines, which include turbojets (early jet engines), turbofans (most military fighters), turboprops (C-130s, Beech King Airs), turboshafts (jet turbine-powered helicopters), propfans (in development, but none currently in production on a specific aircraft), ramjets, and scramjets.
Kerosene was the “original” jet fuel, and remains the principle component in modern jet fuels, which are mixed with a variety of hydrocarbons, including the two most common: naptha, and gasoline. Paraffin oil is also a common component. Gasoline is only used in very cold climates, for its improved resistance to gelling.
You’re right about using jet fuel in piston engines - it’ll run like molasses, if at all.
Jet engines run just fine on pure gasoline (avgas is a grade of gasoline). You’re right about the need to be careful, though. The problem isn’t it’s “volatility,” but the temperature it produces for any given shaft horsepower. It runs hot, so you have to watch your EGT (exhaust gas temperature) carefully. Because of this, in most situations, you won’t be able to develop full power, either, so you have to take that into account when calculating performance facts such as runway length required for takeoff, climb rate, and cruise altitude.
On your point 4 above, some turbine powered aircraft even have approval to use avgas but typically with significant limitations as you’ve described. Basically turbines can use anything that burns while piston engines are more limited in what fuels will work at all.
Are there different brands of Avgas? Like Exxon and co, or do you use what is available at your local airport? I can only assume it comes from the same refinery/pipeline complex as gasoline and diesel and therefore is the same no matter what “brand”.
To add to the confusions, the US Air Force is certifying its jet aircraft to run on partial blends of biofuels.
As far as turbine engines burning about anything, per Richard Pearse, the local utility company recently converted their jet engine powered generators from jet fuel to natural gas. I found that a little unusual as spray patterns in the combustion chambers is pretty important. They must have made a lot of modifications to those engines.
Courtesy of Shell, more than what you really wanted to know about Avgas grades and Jet Fuel types. Avgas. Military Jet Fuel. Civilian Jet Fuels. There used to be higher grades of Avgas. And then there’s weird stuff like the JP-7 the SR-71 used to run on.
A fairly big pdf on aviation fuels and business of same.
EAA’s guidelines if you want to build an airplane that will run on automobile gas or other ethanol heavy blends.
I once heard of a fuel truck operator, who, upon seeing the exhaust of a turbo-prop, promptly fueled the plan with Jet-A.
What should have been used, and how long could that engine have run on pure Jet-A?
This was a few months after the Chevron disaster with 100LL (100 octane, low-lead levels - used for piston planes engines because they:
need 100 octane
cannot tolerate a completely lead-free fuel - they would destruct.
You want to get rid of ALL leaded fuel? Figure an average of $90K/engine + development cost to come up with an engind which operates at max power at 2400 rpm.
I am confused, as I thought that Jet-A was exactly the fuel that you used for a turboprop. Or the new diesel aircraft, for that matter. Do you mean instead, fueling a turboprop with 100LL or something like that? I think mugaliens covered that in point 4 of his post.
Your point on the absolutely hideous cost to retrofit all piston-engine GA aircraft to purely unleaded gas, is noted though, and correct, IMHO. Especially given the wiki for tetraethyl lead, and what it says about the lead concentration in aviation fuel:
Could fuel additives, like are used on old cars, provide similar benefits to lead though? Old cars, or automobile engines generally, are run differently than aviation engines, and I don’t know what problems would occur from lead additives in an aviation engine.
Turbo-props use identical fuel to jets so the fuel truck operator did nothing wrong, unless you got the story mixed up.
I once had a refueller put Jet-A1 into the piston engined Shrike I was flying. The fuel tanks had to be completely drained and the fuel lines purged before it could be flown as it wouldn’t have run at all on the jet fuel.
OK, I’m old and fading fast - this was 20 years ago.
All I can be certain was:
Fuel truck operator treated like “how could anyone be that stupid”
Wrong fuel based on sight of exhaust - at the time, the metal image I had was “that plane’s exhaust looks like a turbo to me”.
As to additives:
How much markup would I need to offset the inevitable litigation when somebody gets confused - say an entire fuel farm getting treated twice.
Chevron bought how many people new engines because somebody left a valve open when it should have bee closed while they ran off a batch of 100LL?
The idea of requiring aircraft to use a fuel additive would be one of the few times you’d see Oil, AOPA, EAA, FAA, and NTSB all on the same side of something.
I don’t know when the standard was implemented, but now overwing refueling ports for jet fuel are racetrack shaped and narrow while the ones for avgas are circular and wider. It *should *not be possible to misfuel a plane, but nothing is foolproof.
Searching for a cite, but my understanding is that one of the most successful aircraft powerplants in history, the venerable Pratt & Whitney PT-6 gas turbine, started life bolted firmly to the ground next to natural gas pipelines. The gas turbines drove pumps which boosted pressure in the pipelines, and they siphoned off some tiny fraction of the natural gas to use as their fuel. Only later were they converted for use as aircraft engines.
Sorry for the hijack, but it appears as if I’m wrong about the origin of the PT6 (it was in fact conceived as an aircraft engine), but there is an industrialized version called the ST6. I’ve also discovered that there are TONS of industrial conversions of aircraft gas turbine engines into compressor and generator sets, including a 50MW bruiser that’s powered by a Rolls Royce Trent, similar to what you might find slung under the wing of an A330. Apparently it’s not all that uncommon for the electrical power on oil rigs to be generated by burning some of the excess natural gas in turbine gensets that utilize engines from retired airliners. It also sounds as if it’s not that uncommon to see these engines run for decades at a stretch.
More (very interesting) discussion on PPRune here.
Resurrecting this thread because of a recent crash.
The aircraft that crashed in Spokane the other day was a Piper PA-46 Malibu. The linked article (at this time) doesn’t say it was mis-fueled, but I heard a mention on the morning news that ‘it should have been fueled with gasoline, not kerosene.’
Natural gas is, uh, already gaseous. Surely you don’t need to do anything but pipe it into the chamber at the same place where the fine mist of jet fuel is made by the spray nozzles. You’d probably remove the spray nozzles and replace them with some kind of orifice with a known diameter, then just adjust the flow rate of gas until the engine runs smoothly.
