Extinction Limit of Lean Premixed H2/CO/Air Flames
This chapter provides a detailed investigation into the extinction limit of lean premixed stretched H2/CO/air flames. Systematic experimentation was conducted detailed the simulation using Chemkin was carried out. Base on the experimental and numerical re
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Extinction Limit of Lean Premixed H2/CO/Air Flames
5.1
Chapter Introduction
Extinction limit is another important property of a mixture. As stated in Chap. 1, there has not been a consistent conclusion on the effect of H2 ratio variation on the extinction limit of syngas/air flames. Thus, this chapter aimed to systematically study the effect of H2 ratio variation on the extinction limit of H2/CO/air flames. At the same time, the critical extinction condition was investigated. In particular, as mentioned in Chap. 1, the extinction limits of weakly stretched flames need to be measured under micro-gravity conditions. Section 5.2 presents the fundamental experimental and numerical results of the extinction limit of lean premixed H2/CO/air flames, especially focusing on the effect of the fuel composition variation. Section 5.3 presents a quantitative assessment on the varied chemical kinetics caused by the variation of the fuel composition, seeking to shed new lights on the chemical kinetic characteristics of the syngas flame extinction phenomena. The extinction phenomena of weakly stretched H2/ CO/air flames, as a special topic, is discussed in Sect. 5.4. Section 5.5 presents a short summary of this chapter.
5.2 5.2.1
Effect of Fuel Composition Variation on the Extinction Limit of Lean Premixed H2/CO/Air Flames Experimental Conditions in the Normal-Gravity Extinction Experiments
The detailed introduction of the experimental and numerical approaches are described in Chaps. 2 and 3. The experiments were carried out at ambient pressure © Springer Nature Singapore Pte Ltd. 2018 Y. Zhang, Propagation and Extinction Studies of Laminar Lean Premixed Syngas/Air Flames, Springer Theses, DOI 10.1007/978-981-10-4615-5_5
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5 Extinction Limit of Lean Premixed H2/CO/Air Flames
Table 5.1 Fuel composition used in the normal gravity extinction limit experiments
NO. E1 E2 E3 E4 E5 E6
Species mole fraction (%) CO N2 H2 2 98 0 10 90 0 30 70 0 50 50 0 70 30 0 90 10 0
CO2 0 0 0 0 0 0
α(%) 2 10 30 50 70 90
(1 atm) and the temperature of the unburned H2/CO/air mixtures was 298 3 K. The fuel composition used in this dissertation is listed in Table 5.1.
5.2.2
Experimental and Numerical Results of the Extinction Limit of Lean Premixed H2/CO/Air Flames
Firstly, the performances of the adopted kinetic mechanisms under extinction conditions of stretched H2/CO/air flames were compared and validated against the newly-obtained experimental data in Fig. 5.1. The computed Kext’s using the three kinetic mechanisms all situated within the error bars of the experimental data when α was small (2, 10 and 30%). However, the predictions with Davis-Mech and Frassoldati-Mech exceeded the lower error bars, underestimating by 15–20% when α was large (50, 70 and 90%). Generally, Li-Mech satisfactorily predicted the extinction limits for all tested cases. Thus, Li-Mech was adopted in the hereafter analysis and kinetic studies. Figure 5.1 also shows that the Kext ~ ϕ curve was shifted left to the lower ϕ region as α increased, implying that t
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