An improved two-color method, which originates from an approximate emissivity ratio model based on the empirical emissivity formula by Hottel and Broughton, was developed to measure the temperature...

Experimental and computational results on the combustion performances and their formation mechanisms were presented and compared in two types of tubular flame burners by using methane as fuel. Results corroborate that the localized stratified tubular flame burner (LSSTFB) can achieve a large stability limit as a consequence of the edge-like flame structure, which is analogous to that of the edge flame. The edge-like flame structure in the LSSTFB is crucial for stabilizing the combustion and differs from that of the rapidly mixed burner. The global equivalence ratio can decrease to 0.18, which is considerably lower than that in the rapidly mixed burner. Additionally, the considerable stability limit can enable the occurrence of low temperature under ultra-lean conditions, whilst the edge-like flame structure can also reduce the NO_x emission through the Fenimore mechanism. On the premise of the ensuring of the burn-off rate, the NO_x emission in the LSSTFB is lower than that in the rapidly mixed burner.

A disc-like gap chamber was developed to investigate the microscale effects on flame propagation characteristics in closed chamber, which is very important to understand the combustion process in micro internal combustion engines. Under initially normal pressure and temperature, the morphology and evolution of outwardly propagating flame, the flammable limit, flame speed and flame instability of propane-air flames influenced by gap width and equivalence ratio were experimentally studied. The results show that, as the gap width nearly equals to the quenching distance, the sustained propagation was possible only with rich flames. The smooth flames and wrinkled flames were observed. It clearly shows that the flame wrinkles developed gradually instead of instantaneously. The flame speed was slower in the 2.0 mm gap chamber than in a conventional combustion bomb, and the flame speed decreased with the increase of flame radius. As a result, the flame acceleration was not observed in present experiments. With the smaller gap width, the wrinkled flame occurred early, and the flame speed was slower. Due to the geometry of disc-like gap chamber, simple theoretical analysis indicates that the heat loss and elevated pressure play important roles in reducing flame speed.

The fundamental investigation on the chemiluminescence characteristics of NH₃-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 NH₃ blending ratios (X_NH3 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 NH₂* were clearly identifiable. As anticipated, the chemiluminescence characteristics of NH₃-CH₄ non-premixed flames were significantly influenced by X_NH3; i.e., the overall signal intensity decreased monotonically within the 200–400 nm band but increased within the 400–800 nm band as X_NH3 increased. The signal intensity characteristics of OH*, CH*, NH*, and NH₂*, indicated by radical images, were consistent with the spectrometer measurements. Particularly, it was found that the intensity ratio of CH*/NH₂* was an ideal marker of initial X_NH3 in present flames, given their sensitivity with X_NH3 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 NH₂* was in the fuel side with a broader distribution zone. An increase of X_NH3 led to greater flame thickness and shifted the peak position of excited radicals far away from the fuel side.