19-02-2011, 11:39 AM
SCRAMJET COMBUSTOR DEVELOPMENT
1. Introduction:
An airframe integrated scramjet propelled vehicle has advantages forapplication to several missions. In its simplest form, such a vehicle will combinethe features of quick reaction, low vulnerability to counter attack and betterpropulsion efficiency.The Supersonic Combustion Ramjet (SCRAMJET) engine has beenrecognized as the most promising air breathing propulsion system for thehypersonic flight (Mach number above 5). In recent years, the research anddevelopment of scramjet engine has promoted the study of combustion insupersonic flows. Extensive research is being carried out over the world forrealizing the scramjet technology with hydrogen fuel with significant attentionfocused on new generations of space launchers and global fast-reactionreconnaissance missions. However, application for the scramjet concept usinghigh heat sink and hydrogen fuels offers significantly enhanced mission potentialfor future military tactical missiles. Scramjet being an air-breathing engine, theperformance of the missile system based on the scramjet propulsion isenvisaged to e nhance the payload weight and missile range.Supersonic combustion ramjet engine for an air-breathing propulsionsystem has been realized and demonstrated by USA on ground and in flight. X-43 vehicle used hydrogen fuel. Hydrocarbon fuel scramjet engine is still understudy and research. Mixing, ignition and flame holding in combustor, ground testfacilities and numerical simulation of Scramjet engine are the critical challengesin the development of scramjet engine.
1.1 Scramjet engine - Technological challenges
a)Mixing, Ignition and flame holding in a scramjet combustor
Among the three critical components of the scramjet engine, the combustorpresents the most formidable problems. The complex phenomenon ofsupersonic combustion involves turbulent mixing, shock interaction and heatrelease in supersonic flow. The flow field within the combustor of scramjetengine is very complex and poses a considerable challenge in design anddevelopment of a supersonic combustor with an optimized geometry. Suchcombustor shall promote sufficient mixing of the fuel and air so that the desiredchemical reaction and thus heat release can occur within the residence time ofthe fuel-air mixture. In order to accomplish this task, it requires a clearunderstanding of fuel injection processes and thorough knowledge of theprocesses governing supersonic mixing and combustion as well as the factors,which affects the losses within the combustor. The designer shall keep in mindthe following goals namely,i) Good and rapid fuel air mixingii) Minimization of total pressure lossiii) High combustion efficiency.
b) Ground test facilities for testing of Scramjet engine.In order to carry out the experiments essentially required for the development ofthe scramjet engine and to clearly understand various complex areas associatedwith it, there is a need of scramjet test facility. Among the devices generally usedto produce the test gas to simulate air entering the scramjet combustor are archeater, ceramic storage heater and combustion burners. The scramjet groundtest facilities are available in the mid Mach number range of 5 to 8. There are nosteady flow test facilities in higher Mach number range since achievement of totaltemperatures, pressure and low pressures at exit present enormous engineeringchallenges. Free piston shock tunnels enable test with duration of onlymilliseconds at higher Mach numbers. Conventional scramjet facilities operate inthe blow down mode since continuous operations implies very large powerrequirement for heating the air.
c) Numerical simulation of Scramjet Flow fieldGround tests and classical methods alone cannot give data with sufficientaccuracy for design of hypersonic systems. Due to the closely integrated nature,component level testing will not be able to simulate accurately the complex flowfield. It is difficult to simulate Reynolds number, boundary layer transition inground test facilities. Also, the quality of air is difficult to simulate in the testfacilities. Therefore there is a need to estimate the performance in the flightbased on the results of ground tests. This can be accomplished only through theuse of mathematical modeling of the flow, which is to be solved to first reproducethe result of the ground test and then used for predicting the flight conditions.The primary unknown on a physical plane consists of modeling turbulence and itsinteraction with chemistry. The issues on the numerical front consist of evolvingalgorithms to solve the N – S equations or their variants such that sharp gradientregions near the shocks are captured with numerical diffusion or overshoot. Theprediction of wall heat transfer rate is another task to be handled both on themodeling plane and numerical experiments. One of the advantages of themathematical model is that once it stands validated it can be used to conductseveral numerical experiments on exotic ideas like with respect to enhancedmixing components with much less expense as compared to experiments. Theexperimental effort is not eliminated but reduced and better focused. This is infact the current day approach to the solution to the problems of high-speed flight.Development and realization of scramjet engine has been undertaken inUSA, Russia, Japan, France, Germany and India individually as well as throughjoint cooperation. The urgency of realizing a hypersonic air-breathing engine hasbeen felt by many agencies for civilian and military applications. Thedevelopment of the scramjet engines poses considerable challenges and itdemands multidisciplinary design, analysis, modeling, simulation and systemoptimization. The hardware realization and testing becomes equally complexand multidisciplinary.DRDL is working on a program called “Hypersonic TechnologyDemonstrator Vehicle” (HSTDV). Technological challenge for this vehicle is todemonstrate the scramjet engine at a flight mach number of 6.5. Numberof ground-based experiments have been carried out to develop the scramjetcombustor and associated test facilities also have been established in DRDL.The details of test facility and tests carried out on the development of strut-basedcombustor, Ramp-Cavity combustor and barbotage injection of kerosene withhydrogen fuel as pilot are highlighted in the subsequent sections.
2. DEVELOPMENT OF THE KEROSENE FUELED STRUT BASEDSCRAMJET COMBUSTOR
2.1 TEST FACILITY:The setup consists of a Hydrogen burner as an on-line gas generator, an axisymmetricconvergent-divergent nozzle for accelerating the test gas tosupersonic speed, a circular to rectangular transition duct. The supersoniccombustor has two parts; one constant area section with backward facing stepwith fuel injection strut and the second one is diverging area combustor. Thevitiated air is allowed to expand through an axsymmetric supersonic nozzle with2.4 exit Mach number. The accelerated vitiated air flows through a transitionduct, to provide a uniform flow at the entry of the constant area combustor, withminimum losses. The total temperature and total pressure of the vitiated airfloware measured by means of temperature sensor and pressure transducerrespectively.
download full report
http://combustioninstitute-indiansectionpdf/SCRAMJET%20COMBUSTOR%20DEVELOPMENT.pdf
1. Introduction:
An airframe integrated scramjet propelled vehicle has advantages forapplication to several missions. In its simplest form, such a vehicle will combinethe features of quick reaction, low vulnerability to counter attack and betterpropulsion efficiency.The Supersonic Combustion Ramjet (SCRAMJET) engine has beenrecognized as the most promising air breathing propulsion system for thehypersonic flight (Mach number above 5). In recent years, the research anddevelopment of scramjet engine has promoted the study of combustion insupersonic flows. Extensive research is being carried out over the world forrealizing the scramjet technology with hydrogen fuel with significant attentionfocused on new generations of space launchers and global fast-reactionreconnaissance missions. However, application for the scramjet concept usinghigh heat sink and hydrogen fuels offers significantly enhanced mission potentialfor future military tactical missiles. Scramjet being an air-breathing engine, theperformance of the missile system based on the scramjet propulsion isenvisaged to e nhance the payload weight and missile range.Supersonic combustion ramjet engine for an air-breathing propulsionsystem has been realized and demonstrated by USA on ground and in flight. X-43 vehicle used hydrogen fuel. Hydrocarbon fuel scramjet engine is still understudy and research. Mixing, ignition and flame holding in combustor, ground testfacilities and numerical simulation of Scramjet engine are the critical challengesin the development of scramjet engine.
1.1 Scramjet engine - Technological challenges
a)Mixing, Ignition and flame holding in a scramjet combustor
Among the three critical components of the scramjet engine, the combustorpresents the most formidable problems. The complex phenomenon ofsupersonic combustion involves turbulent mixing, shock interaction and heatrelease in supersonic flow. The flow field within the combustor of scramjetengine is very complex and poses a considerable challenge in design anddevelopment of a supersonic combustor with an optimized geometry. Suchcombustor shall promote sufficient mixing of the fuel and air so that the desiredchemical reaction and thus heat release can occur within the residence time ofthe fuel-air mixture. In order to accomplish this task, it requires a clearunderstanding of fuel injection processes and thorough knowledge of theprocesses governing supersonic mixing and combustion as well as the factors,which affects the losses within the combustor. The designer shall keep in mindthe following goals namely,i) Good and rapid fuel air mixingii) Minimization of total pressure lossiii) High combustion efficiency.
b) Ground test facilities for testing of Scramjet engine.In order to carry out the experiments essentially required for the development ofthe scramjet engine and to clearly understand various complex areas associatedwith it, there is a need of scramjet test facility. Among the devices generally usedto produce the test gas to simulate air entering the scramjet combustor are archeater, ceramic storage heater and combustion burners. The scramjet groundtest facilities are available in the mid Mach number range of 5 to 8. There are nosteady flow test facilities in higher Mach number range since achievement of totaltemperatures, pressure and low pressures at exit present enormous engineeringchallenges. Free piston shock tunnels enable test with duration of onlymilliseconds at higher Mach numbers. Conventional scramjet facilities operate inthe blow down mode since continuous operations implies very large powerrequirement for heating the air.
c) Numerical simulation of Scramjet Flow fieldGround tests and classical methods alone cannot give data with sufficientaccuracy for design of hypersonic systems. Due to the closely integrated nature,component level testing will not be able to simulate accurately the complex flowfield. It is difficult to simulate Reynolds number, boundary layer transition inground test facilities. Also, the quality of air is difficult to simulate in the testfacilities. Therefore there is a need to estimate the performance in the flightbased on the results of ground tests. This can be accomplished only through theuse of mathematical modeling of the flow, which is to be solved to first reproducethe result of the ground test and then used for predicting the flight conditions.The primary unknown on a physical plane consists of modeling turbulence and itsinteraction with chemistry. The issues on the numerical front consist of evolvingalgorithms to solve the N – S equations or their variants such that sharp gradientregions near the shocks are captured with numerical diffusion or overshoot. Theprediction of wall heat transfer rate is another task to be handled both on themodeling plane and numerical experiments. One of the advantages of themathematical model is that once it stands validated it can be used to conductseveral numerical experiments on exotic ideas like with respect to enhancedmixing components with much less expense as compared to experiments. Theexperimental effort is not eliminated but reduced and better focused. This is infact the current day approach to the solution to the problems of high-speed flight.Development and realization of scramjet engine has been undertaken inUSA, Russia, Japan, France, Germany and India individually as well as throughjoint cooperation. The urgency of realizing a hypersonic air-breathing engine hasbeen felt by many agencies for civilian and military applications. Thedevelopment of the scramjet engines poses considerable challenges and itdemands multidisciplinary design, analysis, modeling, simulation and systemoptimization. The hardware realization and testing becomes equally complexand multidisciplinary.DRDL is working on a program called “Hypersonic TechnologyDemonstrator Vehicle” (HSTDV). Technological challenge for this vehicle is todemonstrate the scramjet engine at a flight mach number of 6.5. Numberof ground-based experiments have been carried out to develop the scramjetcombustor and associated test facilities also have been established in DRDL.The details of test facility and tests carried out on the development of strut-basedcombustor, Ramp-Cavity combustor and barbotage injection of kerosene withhydrogen fuel as pilot are highlighted in the subsequent sections.
2. DEVELOPMENT OF THE KEROSENE FUELED STRUT BASEDSCRAMJET COMBUSTOR
2.1 TEST FACILITY:The setup consists of a Hydrogen burner as an on-line gas generator, an axisymmetricconvergent-divergent nozzle for accelerating the test gas tosupersonic speed, a circular to rectangular transition duct. The supersoniccombustor has two parts; one constant area section with backward facing stepwith fuel injection strut and the second one is diverging area combustor. Thevitiated air is allowed to expand through an axsymmetric supersonic nozzle with2.4 exit Mach number. The accelerated vitiated air flows through a transitionduct, to provide a uniform flow at the entry of the constant area combustor, withminimum losses. The total temperature and total pressure of the vitiated airfloware measured by means of temperature sensor and pressure transducerrespectively.
download full report
http://combustioninstitute-indiansectionpdf/SCRAMJET%20COMBUSTOR%20DEVELOPMENT.pdf
