Study On The Control Law Of Dual Mode Scramjet

Dual mode scramjet engines integrate the performance advantages of ramjet and scramjet engines,which can operate in ramjet mode at a lower Mach number and in scramjet mode at a higher Mach number,so it has a higher performance in a wide-range of flight Mach numbers,and it has become the first choice of hypersonic air-breathing vehicle propulsion system at home and abroad.Due to the wide-range of flight Mach numbers and flight altitude of hypersonic vehicle,the working state of dual mode scramjet engine changes greatly,the working process is complex,and aerodynamic thermo process changes dramatically.So for the sake of controlling the dual mode scramjet engines effectively and accurately,it’s necessary to carry out research on control laws for dual mode scramjet engines while ensuring the stable working range of the engine and maximizing its performance potential.So far,dual mode scramjet engines technology has developed from the ground principle verification stage to the engineering development stage at home and abroad,and the research on control laws of dual mode scramjet engines has become the technical difficulty,which is in urgent need of breaking through at present.This paper centres on the control problems of acceleration and cruise state of dual mode scramjet engines,and conducts the research on the choice of controlled parameters and the design methods of control laws.This paper completed the following work:1.For the establishment of the nonlinear mathematical model of dual mode scramjet engines,this paper completed the research on engine modelling approach based on the modelling of engine components(inlet,isolator,combustor and nozzle).On the basis of the engine nonlinear mathematical model,this paper investigated the performance computation on design point and off-design point of dual mode scramjet engines,and analysed the main elements influencing the engine performance,and gave out the influence rule of the combustor outlet total temperature,the equivalence ratio,and the combustor static pressure on engine performance.This study shows: 1)The nonlinear mathematical model of the engine established in this paper is reasonable and accurate,2)The combustor outlet total temperature,the equivalence ratio,and the combustor static pressure have a monotonous correspondence with the engine thrust.2.For the question of how to select the controlled parameter of dual mode scramjet engines,one-dimensional numerical calculation,two-dimensional numerical calculation and igniting combustion test method on a kerosene fuelled supersonic combustor were synthetically employed,and the research on the selection method of the engine controlled parameters was achieved,and the spatial distribution characteristics of the engine flow field parameters with the changes of the incoming flow parameters and the equivalence ratio were obtained,and the optional controlled parameters of the combustor wall pressure,the total temperature of the combustor outlet,etc.are given out.In the combustor ignition combustion test,the combustor wall pressure,the combustor outlet temperature and the combustor flow velocity were measured by comprehensively using the contact measurement method and the non-contact measurement method.The dynamic characteristics of each parameter changing with time were obtained,and the possibility of application of measurement method in actual control system was analysed.The result of the research shows:1)The engine inner flow field parameters have the features of uneven spatial distribution and dynamic characteristics changing with time.2)The equivalence ratio,the combustor wall pressure in characteristic region,the combustor outlet temperature have a monotonous correspondence with the engine thrust.3)The combustor wall pressure is easy to measure and quick to respond,and has a monotonous correspondence with the engine thrust,which can be chosen as a controlled parameter.4)It’s determined that the real-time position of shock train leading edge can be acquired through measuring the wall pressure distribution of the isolator.3.For the design problem of control laws of cruise state of the Dual mode scramjet engines,two-dimensional numerical simulation method was adopted,the variation rule of the combustor wall pressure under cruise state with single-point and multi-point fuel supply was studied,the design problem of control laws of single-variable and multi-variable cruise state of engine with fuel flow as a control variable was accomplished.And the combustor direct-connect experiment was used to complete the closed-loop control test of single-point and two-point fuel supply and verify the feasibility of the closed-loop control with the combustor wall pressure as the controlled parameter.The result of the research shows:1)During single-point fuel supply,it’s necessary to select the wall pressure at a position as a controlled parameter in the monotonous filed of combustor wall pressure,then the engine state can be controlled.During two-point fuel supply,it’s necessary to select the wall pressure at two positions as controlled parameters in the monotonous filed of combustor wall pressure,then the engine state can be controlled.2)The single-variable and multi-variable control test results show the combustor wall pressure can be well controlled through altering the fuel flow,and the closed-loop control with the combustor wall pressure as the controlled parameter is feasible.4.For the design problem of control laws of acceleration state of the Dual mode scramjet engines,two-dimensional numerical simulation method was adopted,and the engine flow characteristic of each flight state at the acceleration and climb process was studied,and the influence rule of the incoming flow parameters to the flow characteristic of isolator was analysed,the control laws of the engine acceleration state based on the inlet unstart protection was proposed.And the supersonic combustor direct-connect experiment method was used to complete the protection control test of inlet unstart protection and verify the feasibility of controlling the shock train leading edge position of isolator by controlling the isolator back-pressure.The result of the research shows:1)In the process of the engine acceleration and climb,it’s easy to cause the inlet unstart due to the rise of combustor back-pressure at lower flight Mach numbers and necessary to consider the monitoring measures on the design of control laws of acceleration state,which can prevent the inlet from starting.2)It’s fast and accurate to control the shock train front position of isolator by controlling the isolator back-pressure,which can prevent the inlet from unstarting.