Could you run a jet with gasoline? Why do all jet engines use kerosene?
You can persuade a turbine engine to run on just about anything that can burn. So the decision of which fuel to actually use depends on the side factors including, but not limited to:
- hot section temperature
- chemical reactions with engine parts
- Coal dust is rather difficult to pump around, and the rampies don't like shovelling
- liquid hydrogen (used in the Space Shuttle) requires a lot of storage and has the nasty habit of freezing anything it touches, like rampies.
- ethylacetylenedecaborane is unpleasantly toxic (rampies union again) and the combustion byproducts were rather abrasive to the engine's innards
- trimethylaluminum would reduce the engine complexity (no igniters needed) because it has the nasty habit of igniting instantly upon contact with air, so leaks are rather dangerous.
- natural gas is commonly used as a turbine fuel in pumping stations: it's already there and thus is "free". The required pressure vessels make it impractical to use as an aircraft fuel.
So kerosene basically became the standard turbine fuel because it's:
- cheap: kerosene makes up a rather large fraction of crude oil. When you measure your fuel load in tons a few cents per litre makes a difference.
- safe to handle: relatively non-toxic, doesn't ignite all that easily
- storable and transportable in common structural metals
- doesn't clog up the engine
In a modern turbofan engine, fuel is not only burned in the engine and used to lubricate parts such as fuel pumps and controls, it is used as a hydraulic fluid as well -- this is used to power things like inlet guide vanes and variable stator vanes in many engines, as well as more exotic accessories such as movable nozzles and inlet ramps.
This means that gasoline is often not tolerated by larger aviation turbines, as it boils at such a low temperature that it could boil off inside fueldraulic (or other fuel system) parts and interfere with their operation, atop the lubricity and lead fouling issues that it obviously would pose. Even wide-cut jet fuels such as JP-4 and Jet-B are prohibited for service in some larger turbofans due to the volatility issues they pose (this is a quote from the 777 QRH Limitations section):
The use of JP–4 and Jet B fuels is prohibited.
From my training, the limits on the PT6 use of avgas is related to its ability to lubricate the engine's fuel pumps, and the lead fouling of the hot section which will result from the avgas. I can't say about other engine's tolerances, but some military jet fuels have much more volatile components than straight kerosene and marine gas turbines run on diesel. A turbine's fuel isn't always decided by what it can burn, but by what it's practical and economic to feed it.
Apologies if this is tangential but other properties of kerosene (aka kerosine) as turbine fuel were brought up. To my knowledge, all "Jet fuels" (intended for aircraft use) are based on kerosene.
Another property of jet fuel that was not mentioned is freeze point where viscosity drops because of wax formation and pumps and filters begin to clog. Ordinary kerosene (as used in lanterns and space heaters) rarely has to deal with sub-zero temperature (e.g. -40C) and 30,000 feet altitude.
Also important is volatility which can be reduced at low temperatures and impede combustion.
see http://www.shell.com/global/products-services/solutions-for-businesses/aviation/shell-aviation-fuels/fuels/types/civil-jet-fuel-grades.html for different fuels and their freeze points.
The very high temperatures of jet engines cause gasoline to be a poor fuel because it tends to burn too fast. Kerosene, which is routinely called "Fuel OIL" some places, avoids pre-ignition problems (and some safety hazards) just like higher-octane gas avoids spark-plug knocking. The ultimate control of ignition comes from using Diesel Fuel (which ALSO is routinely called Fuel Oil some places), and that's why big trucks use Diesel: that control gives them the best fuel efficiency their engines can have; but Diesel wont' run a jet engine. Gasoline is too volatile for a jet engine; Diesel fuel is not volatile ENOUGH for a jet.
We ran Olympus Gas turbines for fast power and speeds when I was in the Royal Navy. These happened to be the same turbines that Concord used when she was in service. We ran them on Marine Quality Diesel and had no problems.
Again may be its the - temps could be a real issue, and the fact you get more power from Higher octane fuels, with all the technology these days you would think their would be a cheaper alternative.