Every engine needs a catalyst in order to turn the fuel into energy. While most cars on the road (as well as motorcycles, lawnmowers, and other gas-powered vehicles) use a spark plug, a diesel engine like the Ford Powerstroke does not use a spark plug like a traditional gasoline engine, on account of the fact that diesel tends to be more difficult to ignite and burns much slower than gasoline. Instead, a diesel Powerstroke uses a glow plug, a thumb-sized heating device that will use a compression formula to raise both pressure and temperature of air. When the diesel within the fuel tank comes in contact with this high-pressure, high-temperature air, it ignites.
A glow plug uses the same basic formula as a toaster. Within the plug are bands of electrical wiring that generate heat and light on account of the resistance in each band. With greater resistance to the flow of energy (provided by the battery of the vehicle) comes greater heat and pressure, eventually making it hot enough to turn the diesel fuel into energy. Older engines needed to turn from off to start and then to on, since the glow plug could not heat up quickly enough to start the engine. In today’s Powerstroke engines, however, it’s possible to start it up much faster — especially if the engine has recently been running and still retains the warmth needed to ignite the diesel. This is one reason why it is sometimes more energy efficient to allow a diesel engine to run continually instead of turning it off for a certain period, usually around an hour or so.