The cylinders in the internal combustion engine perform the following functions: It forms a closed cavity where the fuel-air mixture is burned.

It acts as the guide of the piston. 

The piston moves the cylinder down under the influence of the force generated by the combustion of fuel.The energy of the formed gas is converted into translational motion, thereby driving the crankshaft.  

In addition, the piston located in the cylinder transmits the gas pressure energy to the crankshaft connecting rod, sealing the combustion chamber and removing heat from it.  

The movement of the piston is facilitated by lubricant from the oil pan.