| Study on deflagration to detonation transition (DDT) is always one of key techniques in Pulse Detonation Engine (PDE) since the PDE concept was presented. A lot of researches focus on how to achieve the shortest distance of DDT. In order to obtain characteristic of DDT, the rule of shock-Flame evolution was studied with hydrogen,acetylene and propane in square detonation tube of 60mm×60mm×2000mm. In this paper some research works have been done and results have been achieved as follow:System of experiment which adapt to single detonation performance study was designed and was established. Photoelectric detector was utilized to measure the flame speed. The results indicate that photoelectric detector is more suitable to measure the flame speed and overcome defect of ion-probe in measuring the flame speed. As a result, deflagration and detonation can be obtained in detonation tube.Evolution rule of wave and flame is key of DDT. DDT was studied from different point of view. Firstly, the process of DDT utilizing different fuel and mixture was performed and contrasted by the means of experiment. The results indicate that the fuel's state and species did not affect essential characteristic of DDT. Secondly, lots of experiments were conducted in order to investigate the characteristic of DDT in close end with 5 kinds of block ratios. The results indicate the block degree does not affect essential characteristic of DDT and only change position of DDT. At last, photoelectric detector was designed to study the process of flame evolution. The results indicate that flame still burn inside detonation tube and time grade of duration was millisecond after detonation wave came out of detonation tube.Detonation structure was systemicly studied in experiment. Firstly, in order to gain the pressure distribution of detonation wave, pressure transducers were installed respectively in different positions to measure the pressure value. The experiment indicates that the detonation wave is not a plane wave. The pressure in tube wall is higher than that in tube center. The results of research help to understand the structure of detonation wave. Secondly, in order to understand the process of shock movement, the conventional soot records were utilized by arranging a window of 60mm×1380mm on side face of detonation tube. Soot records of process of shock movement was successfully achieved, the results break a new path to investigate DDT.At last, the process from ignition to formation of detonation was screened in detonation tube with 60mm×1400mm window. The pressure transducers and ion-probes were disposed according to 50mm space to measure the pressure and flame velocity, respectively. A lots of high speed photograph were successfully achieved in DDT. The simple physics model was predigested from experimental system to study the flame spread process by the means of numerical simulation. Experimental and numerical simulation indicates that hot spots transform detonation in appropriate condition.After realizing some correlative rule on DDT, mechanism of shock-flame interactions, as key content in DDT, was investigated by experiments. Firstly, ion-probe was used to measure the position of flame.The process of shock-flame interactions was analyzed in smooth and filled with obstacle tube. The results indicate that the compression wave occurs always in front of flame without detonation in smooth tube. The flame is in front of shock within the obstacle section, or reversely out side of obstacle section in detonation tube. Secondly, high speed photograph was also used to ensure the position of flame. Relative position between wave and flame was analyzed combining with signal of pressure transducers. Two methods all achieved same conclusion: flame temporarily locate in front of shock wave. Experimental results deeply understand the process of detonation formation.
|
PDF Full Text Request