This chapter deals with the numerical simulation of the exhaust of an engine, passing through a pipe of 100 mm long and 30 mm diameter. The velocity and temperature profiles along with the concentration of exhaust gases are plotted along the axial length of the pipe. Further, a coaxial surface junction thermocouple (10 mm long and 3.25 mm diameter) is placed at an appropriate location of the pipe and the flow field is reinvestigated. In both the cases, the lateral variation of temperature and velocity, are found to be negligible. But, the composition of exhaust gas changes beyond an axial length of 20 mm which may be possibly due to chemical reaction of exhaust gases with ambient air. One of the important objectives of this simulation is to estimate a desired axial location of the thermocouple for a proposed experiment. Based on the simulated results, it found that the thermocouple can be mounted at any axial location between 0-20 mm from the inlet of exhaust pipe.