How A Car Engine Works- Part 1
July 21, 2010 | in Defensive Driving Tips
The exhaust and intake camshafts are the two ovaloid shapes at the top of the cylinder. They regulate the opening of the valves.
The valves are the two plugs below the camshafts. They open to allow fuel in or exhaust out; they close to seal the chamber during combustion.
The spark plug is the coil located between the two valves. The spark plug ignites the fuel-air mixture.
The piston, the square, olive-colored part in the middle of the cylinder, moves up and down in the cylinder to compress the fuel-air mixture and move the crankshaft.
The piston rings (not pictured) create a seal between the piston and the cylinder. This prevents fuel from leaking out of the chamber and oil from seeping in.
The crankshaft, pictured in cross section at the bottom of the image, is a rotating shaft that converts the piston’s vertical motion into the circular motion the car needs to move forward.
The sump (not pictured) contains the oil that lubricates the system. It surrounds the crankshaft.
To power the car, these parts work together in a four-stroke combustion process. This is also known as the Otto cycle, after the German engineer Nicolaus Otto, who built the first car with this kind of engine in the 19th century (an interesting story for another day!)
This process occurs in four steps, or strokes: the intake stroke, compression stroke, combustion stroke, and exhaust stroke. First, remember that the crankshaft is turning throughout this cycle in order to move the piston up and down. Each of these four points in the cycle is illustrated in the image of the cylinder above.
INTAKE STROKE (I) , the intake valve opens. The piston moves down to allow the air and fuel mixture to fill the cylinder. The intake valve then closes, sealing the system.
COMPRESSION STROKE (II) , the piston moves back up to compress the fuel and air mixture in the sealed chamber. This increases the power of the combustion.
COMBUSTION STROKE (III) , a spark from the spark plug ignites the fuel and air mixture. Rather than “exploding” outright, the mixture burns. This causes the mixture to expand rapidly as gases are produced and heated. Since the chamber is sealed, the expansion of the mixture forces the piston down.
EXHAUST STROKE (IV) , once the piston reaches the bottom of the cylinder, the exhaust valve opens to release the exhaust, i.e. the “leftover” gases that remain in the cylinder after combustion is finished.
In a car engine, the cylinders work on staggered cycles. Basically, while half of the pistons are moving on a downward stroke, the other half are moving upwards. Since all cylinders are connected to the same crankshaft, the downward stroke of half the cylinders powers the upward stroke of the other half, and vice versa. Therefore, once the system gets going, it becomes self-sustaining.
So just how does the system get started? That depends on the starter system, which I’ll explain, along with the other components of the engine, in part two.
To learn more about this topic, or a broad range of subjects from “How To Change A Tire” to “How To Jumpstart Your Car”, visit DefensiveDriving.com’s Safe Driver Resources website!
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