Engineering Fundamentals of a Car Engine

The engine is the heart of a conventional car, an arrangement of mechanical parts that converts the energy released by burning fuel into the rotation that ultimately turns the wheels. Its design rests on a few engineering principles: confining combustion in a cylinder, harnessing the resulting pressure to move a piston, and translating that linear motion into continuous rotation.

Inside each cylinder, a piston slides up and down. Combustion of the fuel-air mixture raises the pressure above the piston and pushes it down with great force. A connecting rod links the piston to the crankshaft, which converts the up-and-down motion into the rotary motion delivered to the transmission. Most car engines use the four-stroke principle, completing intake, compression, power and exhaust in two revolutions of the crankshaft, so that one combustion event occurs per cylinder every other revolution.

Valves admit the fresh charge and release the exhaust, and their opening and closing must be precisely timed with the piston's position. A camshaft, driven from the crankshaft, operates the valves through followers and related linkages, a classic example of a cam-and-follower mechanism that turns rotation into the timed lifting of each valve. Engine performance depends on factors such as the compression ratio, the displacement of the cylinders, and the efficiency with which the engine breathes in air and expels exhaust. Different fuels, including petrol, diesel and gaseous alternatives, place different demands on combustion and materials, but the underlying mechanical task of converting heat into rotation stays the same.

Frequently asked questions

How does an engine turn piston motion into rotation?

Each piston is joined by a connecting rod to the crankshaft; as combustion forces the piston down, the rod turns the crankshaft, converting straight-line motion into rotation.

What is the job of the camshaft?

The camshaft, driven from the crankshaft, opens and closes the intake and exhaust valves at the right moments using cam-and-follower action, coordinating valve timing with the pistons.

What does compression ratio mean?

The compression ratio compares the cylinder volume when the piston is at its lowest point to its volume at the highest; a higher ratio generally allows more energy to be extracted from the fuel.