Study On Behavior Of Unstable Combustion Of Lean Premixed Swirl Flame

In recent years, along with strengthening of people’s environmental protection awareness, low-pollution combustion technology has become the focus of research, premixed combustion technology can decrease the emission of NOx and CO, so it has drawn wide attention and development. However, due to the operating conditions deviates the normal chemical equivalent ratio, combustion instabilities, such as blow out and combustion oscillation have emerged as a common problem. It affects the normal work and increases the emission of pollutants, and even leads to damage to the combustion chamber components, has seriously restricts the development of premixed combustion technology.This paper takes the lean premixed combustion process as the investigative object. Then carried on experimental study of characteristics of combustion and pollutant emission at lean premixed swirl combustion conditions. The main research work and conclusions in this paper are as followed:(1) Design and builds the visualization experimental system of lean premixed combustion, records the flame, pressure and temperature by high speed camera, high frequency pressure sensor, temperature sensor and data acquisition unit. The experimental platform is the basis for the experimental research work.(2) The flame structure at different equivalence ratios was analyzed, the results shows that:with the equivalence ratio increased from0.4to0.8, the combustion was transited from unstable to stable states. With the increase of the combustion intensity, the combustion noise level increased from the beginning of62dB to96dB.(3) The presence of the sudden expansion structure and the swirl in the combustion chamber could form the central recirculation zone and the corner recirculation zone. Experiments showed that when the equivalence ratio greater than0.8, it’s easier to induce the generation of tempering, however, the presence of a blunt body effectively suppresses the generation of tempering.(4) Then the lean blow-out at different conditions were measured, the result showed that operating envelope goes forward with the intake air velocity increased. With the velocity increased from2.8m/s to8.6m/s, the lean blow-out decreased from0.5to0.37and the maximum equivalence ratio of stable combustion decreased to0.7from the0.91. (5) The effects of equivalence ratio on the oscillatory combustion were analyzed, it was found that the frequency of oscillation combustion increased and the peak amplitude decreased with the equivalence ratio. When the equivalence ratio closes to the lean blow-out, due to the low frequency oscillation combustion, flame was easily to extinguish. In addition, when fixed the equivalence ratio, the frequency of oscillation combustion increased and the peak amplitude decreased with the intake air velocity.(6) Finally, the component of exhaust emissions at different combustion conditions were measurement and analysis, the result showed that:①The CO2emissions increased while the residual O2decreased with the equivalence ratio increased, the result of investigation of component of O2in exhaust emissions showed that combustion efficiency reached the maximum value when the equivalent ratio equal to0.67, and as the swirl intensity increased, the combustion efficiency also increased. In addition, the generation of NOx also increased from5ppm to147ppm, so the NOx emissions could be reduced at lean premixed combustion conditions.②When keep the equivalence ratio and increase the intake air rate, the NOx emissions decreased since the high rate cause the residence time of the gas in the combustion chamber prolonged.③Change the swirl number from0.8to1.0,the NOx emissions obviously reduced...