Design And Application Of Burner With Stratified Radial Concentration

The study of the combustion characteristics of gas-phase mixtures is the prerequisite for fine control of the combustion process of internal combustion engines.In the cylinder of gasoline engine,the concentration of the mixed gas is often uneven for the fuel can not fully vaporize and diffuse in a short period of time.due to the fuel and injection characteristics,diesel engine with diffusion combustion mode have excessively rich areas and lean zone.as for the new homogeneous compression ignition combustion mode engine,concentration stratified combustion is used to control the heat release rate,so there is a certain level of concentration stratification inside the combustion chamber in a wide range of situations.So the study of the propagation process of flames crossing concentration stratification is of great significance to the analysis of the combustion process of internal combustion engines.Based on this goal,a burner with stratified radial concentration was designed and constructed in this subject,and the verification of the combustion device was performed.The device has been put into practical application to do an experimental research on flame propagation crossing concentration stratification.The specific content of this topic includes:1.Construction of the burner system.The burner system of this subject is developed based on the structure of the McKenna laminar flame burner.A mixture concentration stratify mechanism is added on the basis of the original singleconcentration mixture premixing chamber.The mixed gas is arranged to form a circular nested concentration layered mixture,which flows out from the combustion port to form a radial concentration stratification.The burner system includes 1)the burner,2)a mixed gas supply system,3)a cooling system,4)an ignition system,5)a flame temperature sensing system,and 6)an optical observation system.The burner mainly consists of:(1)a base,(2)a layered mechanism,(3)a ventilated metal plate,(4)a cooling water jacket.In the process of designing the burner body,the size of the burner ventilating metal disc was determined by thermodynamic calculations,and then the size chain of the entire burner was determined.Then,the structure and working principle of the burner layering mechanism were explained.After the design of the burner is completed,other parts of the burner system are set up.The optical observation system achieves the effect of transmitting the side image of the flame and the upper image to the optical analysis device at the same time through a triangular prism and a reflecting mirror.2.Burner system verification experiments.Designed verification experiments for the burner body,cooling system,mixed gas supply system,and light path system,as well as system accuracy verification experiments.1)In the burner body verification experiment,the qualitatively configured lean,rich,and extremely lean mixtures are passed into the burner in 1,3,and 5 layers in different combinations for combustion.Under the conditions of thin layer,third layer thick and fifth layer thin,the flame on the burner surface has obvious stratification,and the usability of the burner body has been verified.2)In the cooling system verification experiment,the maximum heat load condition of the mixed gas equivalent ratio of 1.0 and the inflow speed of 20.91 cm / s was used as the experimental condition.The combustion experiment was continued for two hours,and every half of the first 30 minutes The temperature of the outer wall of the cooling water jacket is measured in minutes,and the temperature of the outer wall of the cooling water jacket gradually decreases.The temperature is stabilized between 27 ° C and 28 ° C during the 24 th to 30 th minutes.The cooling system functionality was verified.3)In the overall test run test of the burner system,combustion experiments were performed under 8 different mixed gas supply schemes,and flame images under 8 operating conditions were collected using the optical path system,and 4 were collected using the temperature sensing system.The flame temperature distribution data under working conditions,the optical image can clearly and completely show the side view and the top view of the flame.The optical path system has been verified.The flame brightness of different levels and the mixing concentration of the mixed gas supply system match the higher the flame concentration The higher the general rule,the mixed gas supply system has been verified,and the flame temperature distribution under different working conditions is between 1147K-826 K,and the flame temperature distribution at different positions is in line with the results in other studies.Burner temperature sensing The system is verified.4)During the verification of the burner system accuracy,the lean flammability limit of the methane-air flame generated by the burner was measured.The measurement results were in the range of equivalent ratios 0.45-0.5,and other research results were in the range of 0.46-0.5 equivalent ratio The experimental results are consistent with other studies,and the accuracy of the burner system is verified.3.Practical application of the burner system.The burner was used to conduct the flame cross-concentration gradient propagation experiment.The experimental objectives were to explore the effects of the layering method,the overall concentration distribution,and the layering gradient on the flame radius,propagation speed,and exothermic percentage curve during the flame propagation process.In the experimental scheme,a total of four kinds of mixed gas supply methods of homogeneous,internal high and low external,high external and low internal,and low intermediate and high internal and external concentrations were designed,and the maximum concentration was designed from 1.0 equivalent ratio to 0.8 for each supply method.Working conditions with different overall concentration distributions of equivalent ratios and working conditions with different concentration gradients from 0.1 to 0.2 equivalent ratios.The high-speed camera was used to shoot the moment of flame ignition at a shooting speed of 500 pps and a resolution of 336 × 800.,And use the image processing method to obtain the flame radius,propagation speed,and the change of the exothermic percentage with time.For example,under the condition that the internal,internal and external three layers of gas mixture are 1.0 equivalent ratio concentration,a total of 5 images are taken during the flame diffusion process,and the flame radius of the top view in each flame image is 5.066 mm,9.983 mm,15.049 mm,19.668 mm,25.032 mm,the calculated flame propagation velocities are 2.53 m / s,2.46 m / s,2.53 m / s,2.31 m / s,2.68 m / s,and the flame exothermic percentage in each image is 2.03%,14.72%,35.16%,63.17%,100%.The experiment obtained the following conclusions: during the radial propagation of the flame,its propagation and exothermic speed are more sensitive to the lowlevel inner layer and low-level layered methods,and less sensitive to the low-level layered layers;When the inner layer concentration is lower than 0.7 equivalent ratio,the initial propagation process of the flame will have a significant retardation phenomenon.When the outer layer concentration is lower than 0.6 equivalent ratio,the final propagation process of the flame will appear a significant retardation phenomenon;the size of the concentration gradient It has little effect on the layering method with low concentration in the inner layer and the layer with low concentration in the outer layer,and it has a more obvious effect on the layering method with low concentration in the middle layer.