Flame emission spectroscopy analysis of distributed liquid fuel combustion

Abstract

Distributed combustion offers ultra-low pollutant emission, low susceptibility of thermoacoustic instabilities, and is highly fuel flexible, being an ideal choice for, e.g., boilers, furnaces, and gas turbines. It was recently demonstrated that Mixture Temperature-Control could also achieve distributed combustion and not restricted to Moderate or Intense, Low-oxygen Dilution combustion. The former approach is employed in the present paper. Online flame control is required by the need for dynamic operation, which is often performed via spectral flame measurements. Presently, the distribution of OH*, CH*, C2*, O2*, and two H2O* chemiluminescent emission peaks were evaluated; the first two represent ignition, while the latter four appear later in the reaction zone. Characteristics of distributed flames are compared to those of straight and V-shaped flames, which are well-known in the literature. The following observations were made. Distributed combustion is lifted and occupies the entire cross-section of the combustion chamber without featuring a characteristic shape. The OH*/CH* ratio shows a low dependence on the equivalence ratio, and the reactions start only 50 mm downstream of the burner lip. The dominant radical was CH* for all distributed flames. As the equivalence ratio increases, the reaction zone moves slightly upstream.