The most simple answer to the question "how does a car start?" is "by turning a key." For many drivers, this is all they ever care to know about their vehicle - they turn the key in the ignition, the engine roars to life, and they go about their day. However, learning exactly what happens when a car starts can be very beneficial for drivers, as it will help them troubleshoot issues on that day everyone dreads - when they turn the key and nothing happens.
For example, most drivers know that without a battery, their car won't start. Yet while there are electric vehicles on the market nowadays, the vast majority of cars are not powered by electricity. So why does a car need a battery, and what role does it play in starting the car?
Turning the key in the ignition essentially sets off a chain of events in the vehicle that begin with the battery. The battery is able to store electric power - mechanical power doesn't really have a way to be stored, so this is the best way to get an engine started without having to crank it by hand.
The key here is the starter solenoid, which is sometimes also called the starter relay. This is a small magnetic switch that receives an electric jolt from the battery when the key is turned. The magnetism is the key for converting the electricity into mechanical energy - the magnet in the solenoid begins the starter motor.
The starter features a small gear with teeth that interlock with the car's flywheel. Once the flywheel is engaged with the starter gear, the engine can really get going. The spinning flywheel turns the crankshaft, which essentially manually starts the engine - as if you were back in the old days and had to crank it by hand. This is the noise you hear when you first turn on the engine.
Yet an internal combustion engine doesn't run on the crankshaft alone. The engine is ultimately propelled forward by small explosions of air and fuel in the pistons. Once the pistons begin moving thanks to the manual crankshaft, the engine cycle has begun and the starter's job is over. It's then the job of the ignition system to keep the engine running.
Drivers hear the term "ignition" and think of where they place the key, assuming that this system is solely for starting the vehicle. Not so. The ignition gets its name because it is continually igniting the air and fuel mixture in the engine to keep the car going.
The main part in this cycle is the spark plug. When the key is turned, electricity is not only sent to the solenoid - it's sent to the spark plug, and continually sent there as the engine runs. The spark plug's job is to make electricity arc across a small gap, and it's this arc of electricity that then ignites the fuel and creates the energy the car needs to run. To complicate things even further, modern cars time these sparks just right so that they are hitting each ignition at the perfect moment to maximize the energy output. When the key is turned off and pulled from the ignition, the spark plug is no longer sent electricity and the engine comes to a stop.
As you can probably tell, there's a lot that goes into starting an engine and keeping it running over time. On a day when your car won't start, keep in mind that it could be any of these parts that are the culprit. Hopefully, knowing how the car starts will allow amateur mechanics to diagnose the problem and find a solution quickly.