| Improving cycle thermal efficiency has always been one of the main objectives of gas turbine research.However,with the improvement of gas turbine-related technology,the efficiency of the compressor and turbine has been very close to its limit,and it has become very difficult to further improve the cycle thermal efficiency of gas turbines.Detonation combustion relies on the advantages of self-pressurization and small entropy increase,which points out a new research direction for breaking through the technical bottleneck of gas turbine cycle thermal efficiency.However,there are still many problems to be overcome before the practical application of detonation engines.Among them,the detonation initiation problem is the most prominent.It directly determines the combustion mode in the combustion chamber and affects the performance of the engine.The low power consuming pre-detonator is a research hotspot in the scientific community.In the past,people tried to accelerate the detonation initiation in the pre-detonator.However,the problems of detonation initiation delay and large structure size caused by slow deflagration to detonation in the pre-detonator have not been overcome.Seeking effective acceleration methods to meet the requirements of engineering applications is bound to promote the application and development of detonation engines.Therefore,aiming at the above detonation initiation problems,a compact detonator based on toroidal shock focusing is proposed in this dissertation.The physical mechanism and the initiation characteristics of the detonator under different initial conditions are revealed by numerical simulation,and the law and mechanism of the influence of detonation initiation and structural factors on detonation initiation are obtained.The details are as follows:（1）Aiming at the problems of initiation delay and large structure size of the pre-detonator,a new and compact detonator based on toroidal shock focusing is proposed in this dissertation.Through the numerical simulation of coupled multi-step chemical reactions,the initiation performance of this structure and smooth tube/blocking tube is compared in detail.It is found that the detonation initiation time of the detonator based on toroidal shock focusing is shortened by 90.8%and 40.8%respectively,The initiation distance is shortened by 96.7%and84.2%,which proves the potential of this detonator in detonation initiation acceleration.The potential of this detonator is confirmed.The purpose is to further analyze the detonation initiation mechanism of this detonator.Through the systematic analysis of the development process of the combustion flow field under typical conditions,the initiation mechanism of this detonator based on toroidal shock focusing is revealed.The research results show that the detonation initiation of this detonator has obvious regional characteristics,and each region plays a different role in the detonation initiation.（2）Aiming at the problem that the change of initial conditions may lead to initiation failure,based on the detonator proposed in this dissertation,the numerical simulation of detonation initiation with different initial pressure and equivalence ratio under the same ignition conditions is carried out.By comparing the results,the detonation initiation characteristics and working boundary of the detonator under different initial conditions are obtained.The results show that increasing the initial pressure will lead to ignition failure,and increasing the ignition energy can broaden the effective working boundary of this detonator;With the increase of equivalence ratio,the detonation wave velocity increases,and the detonation wave surface pressure first increases and then decreases.Whenφ<0.77,it will fail to detonate due to insufficient distance to flame acceleration.（3）Aiming at the problem that the influence law and mechanism of initial ignition on initiation are not clear,and the selection of igniter is lack theoretical guidance,this dissertation studies the effects of ignition energy,ignition duration and ignition diameter on the detonation initiation process and initiation performance using controllable variables.The results show that the detonation initiation time and distance are shortened with the increase of ignition energy,ignition duration and ignition diameter;There is an optimal ignition position conducive to rapid detonation initiation,x0=4mm.（4）Aiming at the problems of optimization of the initiation structure,according to the initiation process and initiation mechanism of toroidal shock focusing initiation structure,this dissertation makes a detailed parametric analysis on typical structural factors in the flame acceleration zone and shock focusing zone.The results show that there are critical obstacles for detonation initiation in the acceleration zone,and the initiation time and distance will decrease with the increase of the number and spacing of obstacles;Only when the dimensionless height of the obstacle is between 0.3 and 0.6,the detonation wave will be triggered.Too large or too small obstacle dimensionless height will lead to initiation failure;The increase of lining depth in the focusing area will shorten the initiation time and distance;The 90°conical cavity surface is most conducive to the rapid formation of detonation wave,and the corresponding detonation initiation time and distance are 330μs and 15.9mm respectively. |
