If a tracer won't set a fuel tank on fire, why are the ragheads burning vehicles to a shell with IED's under the fuel tank. and why are we armoring the fuel tanks on our HUMVEES. If you are aware of the composition of a tracer round and the burning characteristics of said round, you would know that at that temperature, any flammable substance will burn in that environment.
Gasoline flammability limits.
http://www.cdc.gov/niosh/npg/npgd0299.html
UEL: 7.6%
LEL: 1.4%
If the gasoline vapors are above 7.6% inside the fuel tank you can't get it to burn or explode. The fuel vapor displaces the oxygen. Gas vapors in the fuel tanks are going to be above the UEL. The tank has to be ruptured and the fuel dispersed in the air and ignited to get the effects you're seeing. The explosive device does both of these very well and combines the energy of the explosive with the gas.
You're seeing fuel tanks being armored for the same reason that you see the tanks made out of thick enough material to keep road debris from puncturing them. In this case they're trying to upgrade the protection against bullets and schrapinel from explosives instead of standard road debris. If you prevent the fuel tank from rupturing you prevent the fuel from getting out where it can be set on fire.
On the other hand, if you set fire to the vehicle you can heat the fuel in the tank to a point where the tank ruptures if it's sealed or the pressure can not be relieved quickly enough. This is called a Boiling Liquid Expanding Vapor Explosion. You've either got to build a fire under the kettle to boil the fuel or you've got to set a bomb off to blow the fuel tank apart and disperse the fuel to get an explosion.
If you are aware of the composition of a tracer round and the burning characteristics of said round, you would know that at that temperature, any flammable substance will burn in that environment.
I promiss you that what you think is going on is not. If you put an ignition source in the fuel tank, whether it's a tracer or a fuse, it will not cause the fuel to explode because there is not enough oxygen present for the fuel to burn. The vapors displace all the oxygen. This is one of the reason that cars don't just explode all the time. On the other hand, if you punch a bunch of holes in the tank and allow the fuel to escape all the fuel on the outside will burn if you get a source of ignition to the fuel.
If you want to demonstrate this to your own satisfaction there's a very easy test you can perform. Take a standard fuel can and fill it half full with gasoline. Mark off the line between the liquid and the vapor. Drive to a nice isolated place and shoot it below the fuel/vapor line with a tracer. Nothing will happen. No kaboom. Not even a fire. Now shoot it above the line. Still nothing unless some of the leaking fuel outside the can starts to burn.
Let us know what you see.
By the way, we don't use terms like "ragheads" on The High Road. It's part of the issue about being civil in our discussions. There are more rough and tumble sites where ethnic and racial slurs are common but we don't behave like that here.