In case of petrol engine, the mixture of fuel and air in the correct ratio prepared in the carburetor entering into an engine cylinder during suction, but in case of the suction charge is only air from filter. Mixing of air and fuel in diesel engine takes place inside the cylinder at the end of compression.   Improved design of combustion chamber of diesel engine is obtained by imparting Squish and Swirl effects for the modifying part. Also the modifying part must include the hot spot regions at proper locations to improve the performance of an engine and also reduce harmful emissions from exhaust. Therefore, to include the hot spot regions at proper locations, it is required to measure the temperature values at different locations/coordinates on the surface exposed to combustion chamber with the help of thermocouples.