One of the most concerning factor in flight safety is the possibility of the plane erupting into fire due to a fuel spill and a spark. Is it possible---or have researchers ever worked on---to power an aircraft with something that does not set the plane afire?
Airplane engines (reciprocating/turbine) are designed to run on petroleum based fuel. When burned, fuel releases energy in order to power the engines that were specifically designed to be powered by burning fuel. To release its energy the fuel must necessarily "erupt" into a fire. So, the very problem that occurs when an airplane crashes and a fuel-fed fire ensues is the essential component (erupting into fire) that is necessary to power the engine in the first place. If a fuel was created that would not erupt into a fire, then it would not power the engines designed for just that purpose.
But there are other fuel centric avenues for research and development. See a couple in the info below.
The FAA and NASA did some testing of Anti-Misting Kerosene (AMK) in 1984 and intentionally crashed a remotely piloted B720 (like a B707). Along with some other safety improvements being tested, there was a hope that the intensity of post-crash fire using AMK would be reduced enough to permit a higher degree of passenger survivability.
Click the link below to read about the scope of the test and the less than favorable results observed regarding the use of AMK:
After the TWA 800 fuel tank mid-air explosion in 1996, the FAA began a research effort to reduce the possibility of a future similar type event. This eventually led in 2008 to a final rule being issued that required commercial aircraft to implement approved fuel tank "inerting" technology. This technology essentially reduces the amount of oxygen in the fuel tank necessary to facilitate an unplanned ignition source (e.g. electrical spark) from igniting the fuel.
Although this does not change the properties of the fuel (such as adding an AMK component described above), the overall benefit of a less volatile fuel environment adds a great deal of safety.
Read about this "fuel tank inerting" here
Yes, of course, inventors and researchers have always been looking into alternative ways to power planes.
- Rising air: Gliders successfully stay in the air using thermals, ridge lift, lee waves or convergence zones.
- Spring power. Springs can be made of various materials including rubber and steel. Rubber spring power is still popular in toy planes
- Solar power. Experimental planes have been flown successfully with solar cells and electric motors.
Human power: The very first planes were human powered, and there are still inventors trying to push the limits
Fission: The energy density of nuclear fuel like Uranium-235 is even higher than that of chemical fuel. Experiments with fission reactors have been done up to working engine prototypes. The development has been abandoned. The radiation during operation and after waste disposable, leakage, and the risk of uncontained failure are unacceptable. Nuclear fuel does not burn, but fission reactors can melt. Sub systems containing steam can explode.
Fusion: While stationary experiments for fusion reactors are ongoing, so far no practical reactor has been implemented. Fusion does generate radiation as well, but to much less extend and risk than fission. The hot plasma in a fusion reactor cannot grow out of control. However, we still have to see a successful stationary implementation before thinking seriously about fusion powered planes.
Apparently none of first four power sources is used for commercial air transportation, because they are unreliable and/or limiting the range. Fission nuclear power could provide reliability and range, but radiation issues forbid the use of this technology. Fusion remains science fiction for time being.
Instead, chemical fuels are used because of their very high power density, their perceived abundance, and low cost.
Any power storage of high density is potentially dangerous. Just imagine a massive spring that would have enough mechanical energy stored to power a heavy long range aircraft. In case of a mechanical failure, the full amount of energy would be released in an instant. That would be just as disastrous as chemical fuel going into flames.
Treat this as you like, but one of the direct answers to this question (have researchers ever worked on to power an aircraft with something that does not set the plane afire?) is - go nuclear.
It is still possible to start a fire from overheating, but not ball of fire, and not from a sparkle. And don't worry about nuclear explosion: it is remarkably hard to make one, even having a piece of fully enriched uranium or plutonium at hand.
There will be other problems, of course, but nothing is free :)
Biodiesel has a flashpoint as high as 130-140 Celsius. This makes it far less likely to burst into flames.
Ultimately, anything useful as fuel will burn. Even batteries burn - and violently so. It's not possible to eliminate the possibility, but it's possible to greatly reduce it.
Another way to reduce this propensity is structural. There are two major parts to it: reducing the likelihood and the amount of spillage in a moderate crash; and insulating the fuselage against exterior fires.
Currently the focus is on making a post-survivable-crash fuselage survive an external fire long enough for the passengers to evacuate. Needless to say, when you're dealing with a crashed airplane, things will never go according to plan - but at least it upgrades the plan from "everyone dies" to "people die where things other than the crash itself also go wrong".
Is it possible---or have researchers ever worked on---to power an aircraft with something that does not set the plane afire?
Yes. It’s called JP-5. It’s a version of JP-4, that has a higher flashpoint (60 deg C vs -18 deg C). JP-5 was developed for use by the USN, specifically to have a higher flash point for increased safety on aircraft carriers.
JP-4 has now been replaced by JP-8 (flashpoint => 38 deg. C). JP-5 is still in use.