This paper has two parts. The first compares the measured burned gas temperature using Coherent Anti-Stokes Raman Scattering (CARS) with the predictions of a multiple zone computer simulation of combustion. The second part describes a system that is capable of determining the heat flux into the combustion chamber by means of measuring the chamber surface temperature.It is shown that the multi-zone computer simulation can accurately predict the burned gas temperature once the fuel burn rate has been analyzed and the model tuned correctly. The effect of different fuels (methane and iso-octane) on the burned gas temperature is reported. A high burn rate or more advanced ignition timing gave a lower burned gas temperature towards the end of the engine cycle.The surface heat flux was deduced from measurements of the surface temperature by using a finite difference method. From the experimental results, it was found that there are significant cycle-by-cycle variations in the surface heat flux in both the magnitude and phasing. Therefore, a cycle averaged heat flux has significantly different characteristics from a single cycle. These cycle-by-cycle variations in the heat flux were associated with corresponding variations of the propagation of the flame through the combustion chamber. This in turn is due to the variations in combustion. The effects of ignition timing and air-fuel mixture on the surface heat flux are reported. Comparisons between experimental surface heat flux measurements and established heat transfer models show large discrepancies.