Combustion

Combustion... ahhh at last. This is the conversion of chemical potential energy to thermal energy, kinetic energy, sound, and light.  Combustion uses Newton's Second Law of Motion, F=ma, to describe the propulsion of the vehicle. So simple, yet so complex. It also uses the Law of Conservation of Momentum, P1 = P2, because the pistons have mass and velocity, but when they reach the end of their cylindrical shafts,  what happens when they stop moving? Does that mean that the system has no momentum anymore? No, the momentum has only been transferred to the movement of the vehicle (via more systems of course). The spark-plugs use a minimal amount of the energy stored (and recharged via the alternator) to give the kick-off energy required to start a chemical reaction. The Combustion reaction also proceeds to do work on the piston because of the expanding gas from the compression and the explosive nature of the combustion reaction. Approximately 2/3 of the power generated from a typical four-stroke engine is lost power due to loss of heat through the gas in the exhaust pipe and through the coolant system, leaving only 1/3 of the generated power for use. 


The Thermal efficiency, which is what is measured of the fuel consumed versus useful power output is as follows: