PROPAGATION OF LAMINAR FLAMES IN WET PREMIXED NATURAL GAS-AIR MIXTURES

The present work investigates the effect of adding small amounts of hu midity on the inhibition of natural gas-air flames. The inhibition is quantified by measuring and calculating the laminar burning velocities (S-u) of premixed flames from a C-1-C-2 mechanism. The experimental a pparatus consists of a Mache-Hebra burner, equipped with flow controll ers and air purification system. Steam is generated by injecting water into a preheated natural gas-air stream, by means of a syringe pump. The burning velocities are determined experimentally from the schliere n photography using the total flame area. The results indicate decreas ing burning velocities with increasing steam concentration, demonstrat ing the importance of thermal capacity of water vapour on slowing down the flame propagation. There is no indication of flame acceleration d ue to kinetic considerations, even when the flames are doped with minu te moisture loadings. It is shown in the calculations that the laminar burning velocity depends strongly on the number of grid points, and s o a scaling relationship is developed for adjusting the computed value s of S-u. The kinetic model predicts closely the experimental results, but the agreement between the experimental and numerical data is bett er at lower temperatures. The relationship between S-u and the concent ration of the added water vapour, as calculated from the model, is lin ear. For the natural gas considered in this work, the laminar burning velocity at the atmospheric pressure decreases by 1.81 cm s(-1) at 150 degrees C for each percentage point of humidity present in the gas mi xture, and by 1.18 cm s(-1) at 20 degrees C.