Study On Structure And Self-induced Instability Of Laminar Premixed Flame In Low Pressure

As the natural basis of all flames, the studies on laminar premixed flamescontribute to futher understanding on complicated flames. The fast reaction zone will bebroadened effectively in low pressure, which is convenient to do research on the fineflame structure. Flames in low pressure tend to be self-induced unstable, the studies onself-indued flame instability will get rid of other factors which will disturb the flamesand get the mechanism of flame instability and contribute to controling flame instability.This paper studies on the structure and self-induced instability of laminar premixedflame in low pressure through numerical simulation and spontaneous emissionexperiment.In this paper, a planner burner which had the ability to produce flame in lowpressure was designed and a low pressure laminar premixed flame combustiondiagnostic experimental system was set up. By summarizing the studies on chemistrymechanisms of OH(A),CH(A) and C2(d) and evaluating the production rate constants ofproduction mechanisms through the abslute concentration of excited species which getfrom calibrating sponteneouos emission picture by Raleigh Scattering, a spontaneousemission model was found, in which OH(A),CH(A) and C2(d) mechanism can besimulated simultaneously. Judging by the effect of equivalence ratio on excited speciespeak concentration and peak concentration locations, the model agrees well with theexperiment results. Stoichiometry dependence of chemiluminescence peak intensityratio of OH(A) to the CH(A) observed experimentally was clearly supported by thesimulated result.The effect of pressure and equivalence ratio on the structure of laminar premixedflame was investigated by experimental and numerical simulation. It shows that thesequence of the locations of peak concentration of excited species change with the theequivalence ratio. The sequence of the location of peak intensity is OH(A) followed byC2(d) and then CH(A) from the unburnt-gas side in the fuel lean and stoichiometryflame and the sequence turns to OH(A) followed by CH(A) and then C2(d) in the fuelrich flame.The ways to achieve self-induced instability flame in low pressure and the keyfactor which control instability and the effect of different factor on the character offlame oscillation was investigated. It shows that the self-induced instability flame onlycan be found with the fuel rich conditions. The heat transfer between planner flame andthe burner plate coupled with the fuel rich combustion mechanism contributes to flameinstability. The behaviors of instability flame are the oscillation of flame plane in thedirection of gas flow with the emission intensity change periodicly. The key factorwhich controls the instability is the ratio of speed of innet of premixed gas and the speed of flame propagation. The frequency and amplitude of the flame oscillation rely on theequivalence ratio and premixed gas mass flow and pressure.