| Environmental problems have been more significant worldwide in recent years,and pollutant emission restrictions have been increasingly stringent.Low-emission combustion technology has become one of the key technologies limiting the development prospects of the industry.There are some problems in the combustor of light gas turbine,such as small size,high flow rate,large volume heat load,which require short distance,low pressure loss,fast and effective mixing and combustion organization.The lean premixed internally-staged combustion technology has the advantages of compact structure,good combustion stability.It is one of the low-emission combustion technologies with good development prospects.However,the internally-staged combustion technology is subject to the strong coupling relationship between the head geometry and the fuel distribution scheme,which makes the influence mechanism complex,leading to difficulties in multi-stage gas distribution,fuel mixing and combustion organization.Therefore,it is necessary to systematically study the flow and combustion characteristics of the internally-staged combustor.In this paper,aiming at the structural scheme of the internally-staged low emission combustor head,the quantitative analysis of the flow,fuel mixing and combustion characteristics under different controllable geometric parameters and fuel injection schemes is carried out by using the numerical simulation method.The relationship between the characteristic parameters of the cold and hot flow fields is established,and the various rules and prediction methods of the flow and performance parameters in the combustor are obtained.On this basis,the influence of controllable parameters on combustor performance and emissions is systematically analyzed,and a reasonable range of window parameters is obtained.The performance and emissions indicators under typical working conditions are verified in light gas turbine combustors.The main research contents of this paper are as follows:(1)Based on the limitations of design parameters,size requirements and performance indicators,and given the existence of a strong shear layer with a large velocity gradient and strong turbulence with a large vortex scale span in the internally-staged combustor,which may lead to unreasonable streamline distribution and large flow resistance,this paper establishes a basic configuration scheme for the head of air distribution and mixing.The scheme adopts an integrated structure of swirling mixing,which is coaxially arranged between the central pilot stage and two main stages.While reducing the flow resistance,it can ensure that there is enough speed at the outlet to inhibit the occurrence of backfire.The flow field structure of the model combustor is reasonable,and the mixing effect of fuel and air is good.(2)The geometric parameters of multistage swirling mixing heads interact with each other,the influence mechanism is complex,and there is a lack of analysis on the influence of controllable geometric parameters on the performance.In this paper,the numerical simulation method is used to study the influence of controllable geometric parameters on the flow and combustion characteristics of the model combustor.The flow field structure and combustion characteristics of different swirl numbers,swirl directions,spanning angles,the axial distance of the main stages,model combustor size and main stage area ratios are analyzed.By changing the controllable geometric parameters,the combustion efficiency of the model combustor can be more than 99.9%,the pressure loss is less than 2.5%,and the NOx emission is less than 4ppm at the design operating point.After several rounds of cold and hot flow field iteration,the quantitative influence rule and typical control method of flow and performance parameters with geometric structure parameters are given,and the prediction method of cold flow field parameters for the hot flow field is established.It lays a foundation for the staged and zoned combustion organization.(3)Aiming at the flow and combustion characteristics of different fuel injection schemes in a single-head internally-staged combustor,the mixing and combustion processes are studied by numerical simulation.The variation laws of mixing and combustion characteristics in the model combustor under different pilot stage equivalence ratios,main fuel stage stratification ratios,fuel hole diameters,fuel hole numbers,and primary and secondary fuel hole positions are obtained.By combining the effect of the pilot class equivalence ratio and the stratification ratio of the main fuel stage,the influence rules of the changes of equivalence ratio at all levels on the temperature and pollutant spatial distribution under different fuel distribution schemes are obtained.When the pilot equivalence ratio increases from 0 to 1,the NOx pollution increases by nearly 6 times,showing an exponential increase.When the pilot equivalence ratio is high,the stratification ratio has a greater impact on the increase of NOx emissions.When the value class equivalence ratio is 0.6 and 1,the NOx emission increase of the stratification ratio from 0.6 to 1.4 is 5.3 and 9.4 times that of the value class equivalence ratio of 0,respectively.(4)Aiming at the problem that the combustor of the light gas turbine is limited by size and the internally-staged combustion organization is difficult,the performance and emission parameters of the model combustor are comprehensively evaluated to obtain the window parameter range of geometric structure and fuel injection.The internally-staged combustor head with window parameters is used to improve the structure and simulate the combustor structure of a light gas turbine.The results show that the velocity and streamline distribution in the combustor are reasonable,and the temperature distribution in the combustion field is uniform.The combustor performance under each typical working condition meets the requirements,and the streamline distribution is similar,which is suitable for the transition between working conditions.Performance and emission parameters under 1.0 working condition: combustion efficiency is 99.7%,pressure loss is 3.75%,CO emission is 4.0ppm,NOx emission is 17.3ppm,outlet temperature distribution factor is 18.6%,and radial temperature distribution factor is 8.7%. |
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