The acetylene ignition process in combustion thermal spray is typical of a laminar diffusion jet. It has all the features of a free jet. The aim of this research is to obtain the detail sparking ignition evolution process and the chemical reaction time scale and calculate the critical radius and minimum energy input required to produce a self-propagating flame in an acetylene fuel jet. Experiments are carried out by using a unique high-speed continuous CCD camera. The results show that the full sparking ignition time needs about 8 ms and this time scale can be used in the calculation of the flame flow fields in the combustion thermal spray jet.