Auto questions: how car engines work

Car engines, also known as internal combustion engines, are designed to do one thing well- turn a crankshaft.

Car engines have a lot in common with electric motors- they both perform one task very well. Both systems are designed to cause a shaft to spin. The force generated by that spinning shaft may be re-routed to perform other functions, but that is the only specific job of a motor or engine. The amazing engineering involved with a car's engine lies more in how that spinning force is achieved.

A car's engine is properly defined as an 'internal combustion engine'. This means that the motor burns its fuel source within its own housing. Other systems designed to turn a shaft (such as a mechanized pulley) may rely on outside fuel sources to run, but a modern car engine is completely self-contained. The combustion of a gasoline/air mixture creates all the energy a car's engine requires.

But how does an engine generate power? It starts with the fuel source. A very powerful chemical compound called gasoline is stored in a holding tank until needed. When a driver places a key into the ignition, an electrical system is activated. Of primary importance is the powerful electric battery stored securely near the engine. When a key is turned, power from this battery goes to a starter assembly. This is basically a strong electric motor with a large gear (bendix) located in front. The starter's gear meshes with a very large gear connected to the shaft assembly of the engine itself.

As the starter starts to spin the flywheel, a mixture of filtered air and atomized gas is sprayed into a series of cylinders located on the top of the engine housing. This gas mixture is ignited by ceramic spark generators (plugs) located at the top of each cylinder. A car may have 8 or more of these cylinders, so they obviously cannot be ignited at the same time. The idea is to stagger the explosions so that each cylinder pushed down on a valve and piston in a precise order. This is accomplished primarily by a distributor- a device that electronically controls the order of sparking. As the gas in each cylinder explodes, the 'floor' of the chamber is pushed down forcefully. This is actually the top of a piston which is connected to the engine's main shaft. Ideally, each piston pushes down on the shaft just ahead of the next one. The shaft itself is designed with protuberances that mechanically force the pistons back up. This action is much like a bicycle pedal being forced back to the top as the opposite pedal is pushed by the rider. The pistons do their work on the down strokes while the crankshaft forces them back up on the upstrokes. Waste fumes from the original explosion are forced out of the cylinder as the piston returns upwards, and the entire cycle is repeated.

The result of all these pistons bearing down is a spinning crankshaft. This main crankshaft has several gear assemblies attached to it, such as a belt drive that powers the car's electrical and coolant systems. Heat generated by the exploding gasoline and the friction of the pistons rubbing against the metal engine must be controlled. The water pump mechanically forces water and special engine coolant to circulate around the engine block. The ultra-hot water is then recycled through a radiator, which dissipates the heat by spreading it over a large surface area. Cooler water is then recirculated into the engine block.

Another gear assembly from the engine's main shaft meshes with another shaft designed to change the direction of the spin. This is called the transmission, and it is vital for the car's intended purpose of transportation. The connection from the engine to the transmission must be maintained nearly perfectly or else the gears will fall out of alignment and destroy the transmission. The transmission directs the power from the engine to two more sets of shafts called the transaxels. These geared shafts redirect the direction of the spin once more, which allows the tires to move forward and backwards with enough torque to overcome the inertia of a stationary car and create some momentum.

A car's engine could theoretically run forever as long as it had a fuel source and electrical power for ignition. But most engines eventually wear out because of friction and stress. Engine oil helps to keep the valves and pistons lubricated, but eventually leaks develop around critical seals and the engine becomes less efficient. Spark plugs can also become fouled with excess carbon generated by the gasoline, and transmission parts may become damaged over time. An internal combustion is an amazing feat of engineering because the entire system can move with the machinery it powers.