Nitric oxide measurements in DME flames using laser induced fluorescence Master’s Thesis in the Erasmus programme

The aim of the work described in this report is to show and understand the nitric oxide (NO) formation in a dimethyl ether combusting spray. In order to achieve it, optical measurements using laser induced fluorescence (LIF) have been performed in a combustion chamber. The measurements have been carried out using A←X (0, 1) excitation around 226 nm using a dye laser pumped by a Nd:YAG. The fluorescence has been mainly detected in A→X (0, 2) bands using an intensified charge-coupled device camera. Measurements at different times after the start of injection and at different distances from the nozzle have been executed. Later, injection pressure has been increased to quantify its effect on NO formation, measuring at different times at 90 mm from the nozzle. Images from the fluorescence have been processed, using experimental models and corrections for attenuation of the laser beam. The results show that the NO maximum fluorescence (and thus concentration) takes place around 7-8 ms after start of injection at distances far from the nozzle, where the spray is fully developed. The results also show that the NO formation is uniform along the flame, although more fluorescence can be noticed on the lean sides of the flame. Increasing the injection pressure resulted in less remaining NO at that distance from the nozzle. The presence of atomic oxygen in the DME molecule is thought to be the cause of the NO uniform formation. On the other hand, although the results showed a reduction of NO when increasing injection pressure, it is thought that the overall formation must be higher.