How internal combustion engines work
Four_stroke_cycle_compression courtesy of physics.byu.edu
Even if you do much of your own basic car repair and are an expert in the art of DIY maintenance, have you ever given much thought to how a car actually works? Having a basic understanding of the processes that go on under the hood can give you a new found appreciation for your vehicle, and may even make it easier for you to be your own mechanic.
All vehicles on the road use internal combustion engines. It's the engine's job to take advantage of the temperature and pressure caused by the combustion of fuel, and turn that into mechanical energy to move a car.
Your car's engine is divided into cylinders, each of which is a chamber for fuel and air, with a movable piston to change the space available inside the cylinder. Each piston is attached to an output shaft in the engine, whose rotation is what transfers energy to the rest of your car, and allows it to move. Two valves in each cylinder, the intake and exhaust valves, allow fuel and air to enter or leave. There is also a spark plug at the top of the cylinder, which sets off the combustion reaction.
These types of engines are known as four-stroke engines, since there are four phases which take place, each of which corresponds to an upward or downward stroke of the piston.
The first stroke, or inward stroke, is where the piston moves down from the top of the cylinder, creating a drop in pressure. This drop opens a valve which lets fuel and air into the cylinder, and the intake valve closes.
The next stroke, known as the compression stroke, is when both valves are closed, and the piston moves back to the top. This compresses the fuel-air mixture in the cylinder.
During the power stroke, the piston is near the top of the cylinder, and a spark plug at the top ignites the fuel and air, setting off the combustion reaction. This creates enormous pressure, forcing the piston downward very rapidly, and generating the power which runs the vehicle.
Finally, the exhaust stroke takes place as the piston moves upward again, and the exhaust valve opens to release the combusted fuel-air mixture, freeing up the cylinder for another round of combustion.
—Seth Berger
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