The acceleration of a fluid in a Laval nozzle to supersonic speed leads to a significant decrease of the static temperature in the flow, and deceleration via a normal shock results in a sudden reheating. Both effects are used within the joint project PAK 75 (Deutsche Forschungsgemeinschaft DFG) for the homogeneous ignition of a precursor and, hence, for the production of gas phase synthesized nanoparticles with narrow size distribution. However, the shock boundary layer interaction at the desired shock position leads to the formation of a so-called pseudo-shock system. Thereby, the heating rate across the shock system is reduced and the homogeneity of the particle growth is negatively affected by the inhomogeneous downstream conditions. Such pseudo-shock systems have been investigated by many research groups and a comprehensive overview is given by [1].