if we see the valves of an engine .we can observe that there is difference in their sizes.....so why there sizes are kept different.....why not the same????
Incomplete combustion leads to knocking(or more generally we can say detonation).
So, there is need of more oxygen for making the combustion proper.
Hence the inlet valves have larger diameter in respect to that of exhaust valve.
After completion of the expansion process inside the combustion chamber the pressure is very high than the atmospheric pressure .
So,basic physics says that the fluid flows from a region of high pressure to a region of low pressure hence the exhaust will be easily done through the exhaust valves.
But there can be another reason also .
Since the exhaust has to be thrown out of the chamber at a higher speed so ,according to the design consideration if the area is reduced then the velocity will get increased.
So,the burnt out gases will travel at a higher velocity to the atmosphere .
And there will be now no mixture of burnt out gases and fresh air-fuel mixture or air (whichever is applicable).
In intake stroke, the opening is bigger to allow the sufficient amount of air fuel mixture to get in the cylinder because outside presure is less when compared to the inside of the cylinder so it needs large valves. In exhaust, no need for wider opening because the pressure inside cylinder is enough for pushing exhaust gases outside the chambe.
Inlet and exhaust valves have different diameters on most Otto and Diesel engines. The inlet valves have larger diameters to allow the largest volume of air for the engine cylinders. But some engines have 2 or 3 intake valves with slightly larger diameters than the exhaust valves. Equalizing the inlet and exhaust valve diameters reduces the volume of air to the cylinders ..
Basically, intek port is bigger than exhaust.
Cause In intake stroke, the opening is bigger to allow the sufficient amount of air or air fuel mixture to get in the cylinder.
In exhaust, no need for wider opening because the pressure inside cylinder is enough for pushing exhaust gases outside the chamber.
Another reason is that if exhaust port is bigger as exhaust port temp is very high than there will be tendency of auto ignition as higher area leads to more heat transfer.
Did Not Get The Answer?
Contact people of Talent-Mechanical Engineering directly from here