You turn your key in the ignition, and the engine fires up. You press the gas and the car moves forward. You take the key out and the engine turns off. That’s how your engine works, right? It's a lot more detailed than most of us realize, with behind-the-scenes processes taking place every second.
Your Engine’s Inner Workings
Your car’s engine is made up of two main components: the engine block and the cylinder head.
The Engine Block
The block is the bulk of your engine’s size and weight. It is most likely a solid piece of cast iron or aluminum. An inline engine has all of its cylinders arranged in a straight line, most commonly in four-cylinder engines and in some six cylinder setups. A V-block is used in some six-cylinder engines and virtually all eight-cylinder engines. This design splits the number of cylinders into two banks that form a V-shape.
The engine block houses the crankshaft. The crankshaft is a solid piece of precision-machined metal that rotates. It has steps called channels in it that match the number of cylinders in the engine. These are the locations where the piston’s connecting rods fasten to the crankshaft. The power generated in the engine forces the crankshaft to turn, beginning the process of sending power to the car's wheels.
Pistons are fit into the cylinders in the engine block. They move up and down in the cylinders during the engine operation to transfer energy to the crankshaft. Piston rings create a seal in the cylinder to prevent power loss into the engine block. We will look further at the pistons’ operation in a bit.
The Cylinder Head
The upper part of the engine is called the cylinder head. It contains valves that open and close to control the flow of the air-fuel mixture and exhaust gases from the individual cylinders. There must be at least two valves per cylinder: one for intake (letting the unburned air-fuel mixture into the cylinder) and one for exhaust (allowing the spent air-fuel mixture out of the engine). Many engines employ multiple valves for both intake and exhaust.
A camshaft is attached either through the middle or on top of the cylinder head to control the valves’ operations. The camshaft has bumps called lobes that force the valves to open and close precisely.
The camshaft and crankshaft are closely related. They need to operate in perfect timing for the engine to run at all. They are connected using a timing chain or belt to maintain that timing. The camshaft needs to turn two complete revolutions to every single crankshaft revolution. One full rotation of the crankshaft is two strokes of a piston in its cylinder. A power cycle – the process which actually produces the power required to move your car – requires four strokes of the piston. Let’s take a closer look at the piston’s operation inside the engine and the four different steps:
Intake: To begin a power cycle, the first thing the engine needs is the air-fuel mixture to enter the cylinder. The intake valve opens in the cylinder head as the piston begins to travel downward. The air-fuel mixture at approximately a ratio of 15:1 enters the cylinder. As the piston comes to the bottom of its stroke, the intake valve closes and seals the cylinder.
Compression: The piston travels up in the cylinder, compressing the air-fuel mixture. Piston rings seal the sides of the piston in the cylinder to prevent loss of compression. When the piston reaches the top of this stroke, the contents of the cylinder are under extreme pressure. Normal compression is anywhere from 8:1 to 10:1. What that means is the mixture in the cylinder is squeezed to around a tenth of its original, uncompressed volume.
Power: When the contents of the cylinder are compressed, the spark plug ignites the air-fuel mixture. A controlled explosion occurs, which forces the piston downwards. This is called the power stroke because this is the force that turns the crankshaft.
Exhaust: When the piston is at the bottom of its power stroke, the exhaust valve in the cylinder head opens. As the piston travels upward again (driven by simultaneous power cycles occurring in other cylinders), the burnt gases in the cylinder are forced up and out of the engine through the exhaust valve. When the piston reaches the top of this stroke, the exhaust valve closes and the cycle begins again.
Consider this: if your engine is idling at 700 RPM, or rotations per minute, that means the crankshaft is completely turning 700 times per minute. Since the power cycle occurs every other rotation, each cylinder has 350 explosions in its cylinder every minute at idle.
How is the Engine Lubricated?
Oil is an essential fluid in the engine's operation. In the internal engine components, there are small channels called oil passages that oil is forced through. An oil pump sucks engine oil from the oil pan and forces it to circulate through the engine, allowing the tightly-packed metal engine components to run smoothly. This process does more than lubricate components. It prevents friction that produces excessive heat, cools internal engine parts, and creates a tight seal between engine parts like between the cylinder walls and pistons.
How is the Air-Fuel Mixture Created?
Air is sucked into the engine by the vacuum created when the engine runs. As the air enters the engine, a fuel injector atomizes fuel that mixes with the air at an approximate ratio of 14.7:1. This mixture is drawn into the engine during each intake cycle.
This explains the basic inner workings of a modern engine. Dozens of sensors, modules, and other systems and components are at work during this process which enables the engine to run. The vast majority of cars on the road have engines operate in this same fashion. When you consider the precision required to allow the hundreds of components in your engine to operate smoothly, efficiently, and durably for thousands of miles over years of use, you can begin to appreciate the work engineers and mechanics do to get you where you need to go.