Laminar Burning Velocity Measurement Using the Filtered Broadband Natural Emissions of Species

• Published in: Energy & fuels 2020-03, Vol.34 (3), p.3772-3779
• Main Authors: Farhat, A, Kumar, R. E. V, Samimi-Abianeh, O
• Format: Article
• Language: English
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.9b04291

The laminar flame speed plays a fundamental role in understanding hydrocarbon chemistry and is the basis of turbulent flame modeling. The main objective of this research is to visualize a flame and measure its speed using a new optical diagnostic technique, which is based on the natural radiative emissions of various species, mainly hydrocarbons, water, and carbon dioxide. This new technique has two main advantages over the Schlieren method. First, only one optical access is needed, and second, the preheat zone and the flame front can be observed, and their radiative emission can be quantified. In addition, the condition of the unburned gas in front of the flame can be studied using the new technique to evaluate some of the hypotheses behind unstretched flame speed measurement, such as the trivial change of the unburned gas state. To evaluate and validate the new optical diagnostic technique, the flame propagation of methane, oxygen, and nitrogen mixtures was studied using species infrared radiative emissions at broadband wavelengths in the range of 3.239–3.629 μm. The flame propagation was pictured using a high-speed infrared detector under constant pressure condition. The study was conducted at a mean initial gas pressure of 1.005 ± 0.0005 bar, a mean initial gas temperature of 296 ± 1.1 K, and four different equivalence ratios of approximately 0.8, 0.9, 1.0, and 1.1. The flame speed measured using the new technique aligns well with the measured data from the literature using the Schlieren technique and simulated data using a detailed mechanism at the studied conditions. The measured data also show the presence of the radiative emission from the unburned gas. This observation contradicts the assumption of trivial temperature change of the unburned gas mixture during the flame propagation, which is widely used for unstretched flame speed measurement relative to the unburned gas state.