How Does a Car Engine Start?by Steve Smith
A car engine starts thanks to the ignition system. This is the unit that supplies the energy to get the motor going. The ignition system begins with a key, which you insert and turn, and ends with a spark that ignites combustion in the cylinders. This combustion is what starts the engine. It is important to note that everything up until the moment of combustion in the car cylinders is part of the ignition system.
What Happens When you Turn the Key
When you start the car by turning the key, several parts are set into motion. First the starter motor comes to life, then the engine begins to turn and the spark plugs fire. When the key is turned, the starter motor "turns the engine over," which means it turns the crankshaft which in turn gets the pistons moving in the cylinders. This starts the engine cycle. Air and fuel is drawn into the cylinders, it is compressed and the then the spark plugs fire. This begins combustion.
About the Engine Cycle
When you first turn the key you may notice your engine makes a grating, heaving sound. This is the sound of crank shaft turning and pistons moving, which begins the engine cycle and compression. Without this, the car would not be able to start the chain reaction of combustion that keeps it running under its own power. If your car doesn't start their may be something getting in the way of this process, like no fuel, low battery (your battery supplies the power to the starter motor) or a clog in the engine system.
Problems Starting a Car
All the parts of the engine must be perfectly timed in order for it to start correctly. If one part is off, then the engine will have problems starting. The air intake and fuel valves must open at a precise time to supply fuel so it can be compressed and the spark plugs must fire right at the height of compression for optimum power. If they fire too slowly, the engine under-performs, and if they fire before the fuel is brought into the cylinder, the car may not start at all.