Winter Flying – Engine Fire on Startup
Its wintertime. (At least it was when this was written-I don’t know when you might be reading this.) But winter means cold temperatures and cold starts to your engine. And cold starts can often lead to an engine fire…
Gasoline doesn’t evaporate as quickly when it is cold, and that makes it much harder to burn. Your battery doesn’t work as well when it cold either meaning the starter has to work against the lack of energy being given to it. And then too your engine oil is thicker, slower moving, causing your engine to turn slower while cranking it.
So imagine yourself in this situation, sitting on the ramp, cold. You want the engine on because engine running means heat in the cabin. On a normal day you would probably prime the engine a couple times, crank it over and it would be good.
But because of what we described above, the engine appears to not want to start. Which often leads to a very dangerous thing: over priming.
When you prime the engine you are putting gas into the intake manifold to get the cylinders ready to fire up. But when you over prime you end up putting too much fuel into the intake manifold, but also the valve chamber and even into the cylinder itself.
Then what happens? It sits there. The reason is that for an engine to start it needs the right fuel to air ratio. But when you over prime that ratio gets off and ignition wont happen. Then excess fuel can pool in the engine as a liquid.
As the fuel becomes liquid in the engine, for instance in the cylinder, it sloshes around creating a smaller fuel to air ratio, and when it finally does ignite; it tends to ignite with a fury.
As the sloshing fuel ignites it tends to go two places: the exhaust manifold, which is fine. But potentially it will travel to the intake manifold. This is bad. This can cause the burning fuel to run down into the carburetor or fuel injector assembly and actually burn through them.
So what can you do to prevent an engine fire if you happened to over prime? And what can be done if an engine fire does happen?
Obviously prevention is the preferable method. Typically, if you are over primed you will be able to smell fuel. And if it is really bad you may be able to see it dripping from the exhaust pipe.
If it is that bad you should not start the airplane. Give the engine time to evaporate the extra fuel. Open the throttle to full, which will open the engine butterfly valve allowing air through the engine and helping the fuel to vaporize.
If you are unlucky enough to experience a fire on startup, make sure you already have to proper procedure for your aircraft memorized. A sudden fire is no time to pull out the POH and start reading. Typically though it will be some variation of these basic steps:
Fuel Selector Off
Continue Cranking to pull the fire into the induction system.
So remember, over priming is the leading cause of engine fires on the ground. Stick with the normal starting procedure. It will be better in the long run.
Stay with us for more posts like this. I will be posting again about some more helpful tips that will help you save money while you fly!