A combination of numerical simulations and experiments is used to establish the accuracy of a soot production and the associated radiative heat transfer models for a non-buoyant laminar diffusion flame. In addition, the need to describe the combustion reaction by means of finite rate chemistry is assessed. An ethylene flame is established within a laminar boundary layer flow and the physical parameters studied are the flame length and standoff distance. Experimentally, these parameters are defined by means of CH chemiluminescence measurements. The results show that finite chemistry is necessary to define trailing edge quenching and thus the flame length. In the absence of accurate local soot concentrations and a robust radiation model, the standoff distance and flame length cannot be predicted accurately. © 2006 Energy Institute.