The internal combustion engine is one of the most widely used methods of converting chemical energy into mechanical energy in our everyday lives. From powering automobiles to generators to airplanes, they truly are everywhere. But that begs the question — how do they work? How do they turn dead dinosaur liquid (gasoline) into little explosions that move our cars? As a mechanical engineer with an interest (let’s avoid the word obsession) in cars, I’m hoping to answer these questions for you today.
I’m going to focus on four-stroke gasoline spark-ignition engines for now since those are what are typically used in today’s cars… and I like them the best. That may have sounded like a bunch of jargon before, but it’ll all make sense within the next 450 or so words, I promise.
The essential parts of an engine that you’ll need to know are the piston, cylinder, intake and exhaust valves, and spark plug. Pistons are the cylindrical metal bits that slide up and down in the cylinder, which is the housing for the entire combustion cycle. The valves do exactly what they sound like — they let air into and out of the cylinder at carefully controlled times. The spark plug ignites the entire mixture with a little arc of electricity to begin the little explosion that drives the entire process.
Let’s go about this by breaking down the name piece by piece. “Four-stroke” refers to the number of times each piston moves up and down in its cylinder to complete one operating cycle. Those four strokes are the intake, compression, combustion, and exhaust strokes. A good way to remember it is, “Suck, squeeze, bang, blow,” if you’re about as mature as I am. The intake stroke is when the intake valve opens up, and the piston first moves downward in the cylinder, creating a vacuum that draws the air and fuel (gasoline) mixture into the cylinder, mixing it all up so that it can explode as cleanly and evenly as possible. Next is the compression stroke. This is when the intake valve closes, and the piston moves back up the cylinder, squeezing that air and fuel together to allow for a more efficient explosion. This is followed by the combustion stroke, where the spark plug at the top of the cylinder ignites the compressed air-fuel mixture (thus, “spark-ignition”), pushing the piston back down the cylinder and rotating the crankshaft, which is connected to the transmission and rotates the wheels of the car. Finally, the exhaust valve opens up, the piston slides back up the cylinder, and the byproducts of the combustion event are pushed out of the cylinder and out through the exhaust system. This process repeats itself thousands of times per minute, creating the rotary motion that moves our vehicles by exploding little bits of fuel.
So now you know how an internal combustion engine works! Wasn’t that fun? I know, I think so, too.
