- The shape and geometry of the combustion chamber is very important from the point of view of creating turbulence in the combustion space. As the air enters through the air inlet valve, exhaust gas is blown out through the opened exhaust valve. During this time, the incoming air will always follow the geometry of the combustion space.
- The geometry of the combustion space governs the movement of the incoming air and exhaust gas. This creates a large amount of turbulence, which will be useful in the proper combustion of the fuel, and thus increase the thermal efficiency of the engine.
- Also, turbulence is created because of the shape of the crown of the piston which is part of combustion chamber geometry.
- As the air enters the chamber, it will hit against the crown of the piston and create turbulence due to change in direction, leading to greater combustion of the fuel.
Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.