Internal combustion (as in compression ignition engine). The fuel-air mixture is ignited in the cylinder either by an electric spark (as in ignition engine) or by compressing air (as in compression ignition engine). The gas formed pushes the piston down.
Thrust – the force that propels an object in given direction, especially when generated by the object itself, as by an engine or rocket
Specific impulse – specific impulse is the thrust per unit amount of fuel burnt per second.
Propulsion– propulsion is a means of creating force landing to forward movement
Rocket propellants
Rocket propellants are high oxygen-containing fuel or mixture of fuel and oxidant which burn in define and controlled manner to produce a large volume of gas.