Internal Combustion Four Stroke Motor

Daniel Starwalt
January 22, 2015

Submitted as coursework for PH240, Stanford University, Fall 2014


Fig. 1: Nikolaus August Otto. (Source: Wikimedia Commons).

The Internal combustion four stroke motor is and has been powering cars and other motorized things since it was invented in 1864. The idea of an internal combustion motor had been around for many years before, but Nikolaus Otto was the first one who was able to make the idea practical. [1]

Internal Combustion

The internal combustion four stroke motor is what powers almost all of the cars on the road today. It may seem complicated, but it is really a simple process. It uses the idea of internal combustion to provide power. The idea of internal combustion is just that of harnessing the power of an explosion from within a confined space. One simple example of internal combustion is that of a potato launcher. You take a tube, cap off only one end, spray a combustable aerosol spray or other propellant into the tube, insert potato into tube, ignite the propellant in the tube, and watch potato fly. [2]

How Does It Work?

The four stroke motor, is a little more complicated than the potato launcher example, but it follows that same basic principles of internal combustion, insert fuel into contained chamber, ignite fuel, and use the energy from the combustion to power your car.

Fig. 2: Four Stroke Cycle. (Source: Wikimedia Commons)

If you look at Fig. 2 you will be able to see a diagram of a four stroke cylinder.The Piston moves up and down inside of the cylinder of the motor block. This movement is timed very specifically with many other factors. First the piston moves up and down because of the rotation of the crankshaft underneath of it. As the piston moves up and down in the cylinder, the volume in the cylinder is constantly getting larger or smaller based off of the movement of the piston. As the piston starts from the top of the cylinder, and moves down, there is a valve that opens called the intake valve, this intake valve allows for a mixture of gas and air to be let into the cylinder on top of the piston as it is descending. This is called the intake stroke of the motor. Next there is the compression stroke of the motor. That is when the piston starts to move back up towards the top of the cylinder and compress the air/fuel mixture. Third comes the Combustion stroke, this happens when the piston gets to the top of its stroke, and the spark plug sparks to ignite the air/fuel mixture. The combustion forces the piston back to the bottom of its stroke, where the exhaust stroke occurs. Once the piston hits its lowest point in its stroke, an exhaust valve is opened allowing for the exhaust to escape. After this the entire process is repeated on every cylinder your motor. Most cars these days have either 4 cylinder 6 cylinder or 8 cylinder motors, this means that there are either 4, 6, or 8 sets of pistons and cylinders in your car, repeating the four stroke process, over and over at extremely fast speeds.


The four stroke motor has been here for a long time and I foresee it being here for an even longer time. There may be other alternative energies to your average four stroke motor vehicles, but those are costly, and will not last the sands of time. The internal combustion four stroke has powered through over a hundred years, and is reliable and powerful enough to stay around for over another hundred years.

© Daniel Starwalt. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] D. Sherman, "A Two-Stroke Revival, Without the Blue Haze," New York Times, 17 Dec 09.

[2] P. Green, "They Shoot Potatoes, Don't They?" New York Times, 10 Jul 13.