Where Does Propane Come From?
Propane (C3H6) is a flammable, hydrocarbon gas commonly used for grilling and heating. A constituent of crude oil, propane is isolated and packaged through a process known as "fractional distillation" wherein the liquid crude is put under pressure and heated inside a tall, sealed tank to propane's boiling point. As the propane evaporates, it is suctioned out through a one-way valve at the top of the tank. Then it's pressurized and cooled until it condenses back into pure, liquid propane. A machine then pours this liquid into a vacuum-insulated, pressurized tank for distribution into smaller tanks (e.g. those you pick up and drop off at the hardware store for "refills").
From Tank To Burner
Propane is transported as a liquid purely for convenience's (i.e. the volume of the liquid form takes up a fraction of the gas' form). To hook the tank up to the grill, the end of a tube leading to the burn is screwed securely onto the threaded opening of the tank. Once this connection is secure, the tank's top valve is turned counter-clockwise, exposing the tank's high-pressure interior to the tube's low-pressure interior. As the pressure equalizes, some of the liquid propane evaporates and fills the tube. Meanwhile, the burner side of the tube has a special valve that keeps this newly-evaporated gas from escaping. This special valve is controlled by a dial on the front of the grill, allowing the user to adjust the amount of propane, which determines flame strength.
Igniting the Burner
The burner consists of a single inlet pipe that opens into a shallow, dome structure with small holes surrounding its base. Above one of these holes is a spark generator designed to ignite the escaping gas. Once ignited, the heat from this initial fire creates a chain reaction that lights every single hole around the burner.
The spark generator uses "piezoelectric" quartz crystal, meaning that it has the ability to convert different kinds of force into electrical voltage. For this particular type of piezoelectric behavior, a small, spring-powered hammer inside the grill strikes the bottom of the quartz with such force that the resulting voltage discharges across the air, "arcs," into the metal of the burner below.
Turning Off The Burner
To extinguish the burner, the user simply turns the dial to "off." This completely stops the flow of propane, causing the flames to go out. Turning the gas flow back on will not re-ignite the flames. Rather, the spark generator needs to fire simultaneously with the new flow of gas.