Liquid propellant rocket engines are very complex machinery and require immense research time to obtain the best performance possible. Therefore its performance efficiency has to be determined based on the various losses that occur during its operation. This research aims to measure the boundary layer efficiency caused by friction losses at the boundary layer formed between the fluid flow and wall surfaces. The boundary layer efficiency is being determined for a rocket test engine operated by the Institute of Flight Propulsion at the Technical University of Munich. The research was done numerically using the computational fluid analysis software ANSYS CFX [3]. Initial results were obtained by assuming fully combusted hot flow entering through the propellant injectors. Next a few methods were tested by supplying the combustion energy to the cold fluid flow as it entered the combustion region. Two methods using a volume source and a surface source were found to work perfectly though they created different combustion flows in the combustion region. Overall the volume source created a more logical fluid flow and also required less time for convergence of results. It should still be verified by simulating chemistry reaction of the propellants.