Experimental Study on Chemiluminescence Properties of Ammonia-Methane Non-Premixed Laminar Flames

The fundamental investigation on the chemiluminescence characteristics of NH 3 -based flames is essential for the development of low-cost, real-time optical diagnostic sensor technologies. In this study, we have experimentally examined the chemiluminescence properties of non-premixed ammonia-methane laminar jet flames under various initial NH 3 blending ratios ( X NH 3 from 0.2 to 1.0 in volume) by conducting the emission spectrum analysis within the 200–800 nm band and capturing the distribution images of key excited radicals. The results revealed that the emission spectra of OH*, CH*, CN*, NH*, and NH 2 * were clearly identifiable. As anticipated, the chemiluminescence characteristics of NH 3 -CH 4 non-premixed flames were significantly influenced by X NH 3 ; i.e., the overall signal intensity decreased monotonically within the 200–400 nm band but increased within the 400–800 nm band as X NH 3 increased. The signal intensity characteristics of OH*, CH*, NH*, and NH 2 *, indicated by radical images, were consistent with the spectrometer measurements. Particularly, it was found that the intensity ratio of CH*/NH 2 * was an ideal marker of initial X NH 3 in present flames, given their sensitivity with X NH 3 and relative ease of measurement with the cost-effective sensors designed for invisible wavelengths. Moreover, in the flame front, CH* was located in the oxidant side, while NH 2 * was in the fuel side with a broader distribution zone. An increase of X NH 3 led to greater flame thickness and shifted the peak position of excited radicals far away from the fuel side.