Research On Flame Characteristics Of Methane Swirl Combustion

Gas turbine is a kind of power machine which transforms thermal energy to mechanical energy,it has been widely employed in industry.It is of great significance to develop gas turbine for assuring national security and energy security,improving energy structure and environment.In recent years,the state has set up a major project to independently research and develop gas turbine.To achieve this goal,basic research has to be carried out first.Flame characteristics including flame shape and size,flame oscillation,and pollutant emissions are important topics in the fundamental research field of gas turbine combustor.In this dissertation,these three aspects were explored mainly by performing experiments using a combustion test rig.numerical calculation and theoretical analysis were adopted in part.The main conclusions are listed as follows:In regard to flame shape and size,the effects of operating parameters on flame appearance and size were investigated.It was found that,as fuel mass flow rate enlarged.flame shape extended and widened,flame length increased and had a linear relation with fuel mass flow rate.As combustor pressure enlarged.flame shape became shorter and wider,flame length diminished and had a power relation with pressure.As primary air mass flow rate enlarged,flame shape became shorter and narrower.As the nozzle exit velocity enlarged,flame length and width remained mainly unchanged.To collectively consider the influences of varying operating parameters at the same combustor pressure,the primary air mass flow rate to fuel mass flow rate ratio was used.as it enlarged,flame length and width generally decreased.CFD and theoretical analysis show ed good prediction of the varying trends of flame shape and size.In regard to flame oscillation,firstly,the oscillating dynamics was analyzed,and the impacts of operating parameters on flame oscillation were investigated.It was observed that,as fuel mass flow rate enlarged,the frequency increased and the amplitude decreased.As combustor pressure enlarged,the frequency diminished and the amplitude uniformly amplified.As the primary air mass flow rate enlarged,the frequency became smaller and the amplitude varied non-monotonously.As the injector exit velocity enlarged,the frequency decreased almost linearly and the amplitude remained basically unchanged.The frequency spectrum of swirl combustion has multiple peak values,this is different from non-swirl combustion which has a single-peak spectrum;and the frequency of swirl flame was more sensitive to the variation in operating conditions than that of non-swirl flame.Secondly,the oscillation of flame properties was explored,almost every spectrum showed two basic frequencies:it can be inferred that the flame oscillation in width direction is stronger than the oscillation in length direction,so the flame oscillation is primarily attributed to the oscillation in width direction.Lastly,spatial analysis and global analysis were performed for oscillation parameters,the coefficient of variation was firstly used to measure the oscillation intensity.It was concluded that,the oscillation at flame edge are the fastest and strongest:the number distribution gradually tends to normal distribution at higher fuel mass flow rate.In regard to pollutant emissions,firstly,the influences of pressure on NO and CO were investigated.It was found that,as pressure P increased.NO became smaller proportionally to-0.53,which is primarily attributed to the impact of global flame residence time,the NO almost enlarged proportionally with the increasing global flame residence time;CO declined proportionally to P-0.35 Secondly,the influences of reaction mechanisms on high-pressure NO calculation were studied numerically,as well as the calculation for prompt NO.It was concluded that,the NO formation from simplified mechanism Skeletal mech showed high consistence with that of original mechanism GRI3.0,with less calculation time(half of GRI3.0);and the result of modified mechanism GRI3.0 modified is more accurate than that of original mechanism GRI3.0,with the same time consumption.The addition technique and subtraction technique were verified,these two methods are correct for calculating prompt NO formation;the prompt NO formation rate from NCN sub-mechanism is larger than that of HCN sub-mechanism,the exit NO concentrations from the former are double of the latter.