GASOLINE ENGINE

Gasoline Engine
     Gasoline engine is classified into two, first is the 2 stroke engine and the other is the four stroke engine. Two stroke gasoline engine consist only of two processes in order to complete one cycle while the four stroke consist of four processes.
     The processes involve in two stroke engine are compression and combustion process. Since there are only two processes per complete cycle the fuel pass through with less oxygen. Lack of oxygen in the fuel affects the performance of the engine. To make this clear, assuming that the fuel and oxygen ratio is enough, after combustion as a result of chemical processes, the product must be Carbon Dioxide or CO2, because of lack of oxygen in the two stroke engine, the product becomes Carbon Monoxide or CO. In two stroke engine some of the product becomes carbon dioxide and most is carbon monoxide which is a black smoke coming out from a two stroke engine. Lack of oxygen results to incomplete burned of fuel, meaning that some of your fuel is just a waste. 

Idea of Construction 
     Consider a four stroke gasoline engine.

 

         Fuel inside the engine chamber consist of mixture of gases so lets start first if properties of solid, liquid and gas because it has relevant effects on the engine.

Solid
    Molecules are rigid, and compact together. Higher melting points(metals).
Liquid
     Molecules are farther than those solid, expands if heated and has lower boiling points.
Gas
     Don't have definite shape, molecules are farthest among the three,. Easily expands in high temperature.

     For better understanding, lets assume that our matter(solid, liquid, and gas)  is an ideal, that they obey ideal laws of matter.
     In the first stroke, the intake stage. The intake valve is opened and the engine is allowed to absorb the maximum volume of air together with the fuel. The fuel and air mixture is enough to have a complete combustion. There is no reaction yet.
     In the second stroke, the compression stage. The intake valve is closed and the fuel-air mixure is compressed to its minimum volume. Since the process is instant, we can say that it is and adiabatic compression(no heat loss or heat absorption takes place). In adiabatic compression the temperature of the air-fuel mixture rises, enough to energies the air-fuel mixture and ready for ignition stage.
     In the third stage, the ignition stage. In this stage the spark plug ignites the high temperature air-fuel mixture and expands the gas adiabatically. The instant explosion produce a strong pressure on the piston of the engine and resulting in the rotation of the shaft.
     In the final stage, the exhaustion stage. The exhaust valve is opened and the by-product is exhausted completely. This stage is a preparation for the next cycle and the process continues.
 The shaft will continue to rotate  because after the third stroke there still inertia  (it will continue to rotate, unless it is stop) remain in its shaft.