Rocket Engine Combustion

Combustion in Rocket Engine and

Its CFD Modeling


Dr. Sharad N. Pachpute (PhD, IIT Delhi)


Modeling the Combustion System with Highest Thrust To Weight Ratio


1. Introduction to Rocket Engine Combustion

  • Rocket engines are widely used for satellite launching and space mission for various applications such telecommunications, weather forecasting and military purpose.
  • Rocket engine is placed at the bottom part of space vehicle where the combustion chamber is a heart of rocket engine
  • High velocity and temperature exhaust gases passed  through combustion and expansion through nozzle of suitable fuel and oxidizer mixture.

 2.Principle of Jet Propulsion 

  • In a rocket engine, the source of oxygen is called an oxidizer. The oxidizer  and fuel are mixed  and burn a combustion chamber.
  • The high temperature and pressure gases produced from combustion  are allowed  through a nozzle at very high velocity. That creates a upward thrust.
  • There three types of propellant are used in rocket engine: solid, liquid and gases
  •  In a solid propellant are less efficient compared to liquid propellant but they can be stored for a long time without degradation.
  • Solid Propellants are heavier than liquid propellant. Hence, most of rocket engines use solid propellants initially followed by liquid propellant for thrust generation.
  • The following figure show the physical understanding of action and reaction principles
  • Rocket propulsion system works on the principle of thrust generated by high velocity jet, gravity and drag forces
  • The thrust is generated due to expulsion of high pressure and temperature flue gases from the nozzle

3.Classification of Rocket Propellant

rocket propellants

3.1 Solid Propellant Rocket

  • This rocket engine uses  sold fuels which is called as solid propellants
  • Solid propellants are in composites forms which can be homogeneous mixtures of one or more  chemicals
  • Composites typically are  a mixture of granules of solid oxidizer
  • Solid Propellant consist of one or more ingredients:
    • Polymer binder with flakes or powders: ammonium nitrate, ammonium per chlorate, potassium nitrate
    • Energetic or explosive compounds: RDX, HMX
    • Metallic Additives: Aluminum, Beryllium
    • Burn rate modifiers: iron oxide, copper oxide
Idealized solid propellant rocket. Major components are indicated ...
  •  In a solid propellant rocket engine, igniter is used to burn the solid propellant
  • The high velocity flue gases are allowed to pass through the exhaust nozzles to produce the thrust
solid-propellant rocket motor
  • Schematic for Combustion chamber of Solid propellant rocket engine
  • Thrust vectoring mechanism is provided to control the direction of nozzle and flue gases
Solid Rocket Propulsion"
  • Solid propellant rocket 
Rocket Fuel - Solid Propellant Rocket
  • Application of Rocket Engine
    • Missile and military applications
    • Launching of light weight satellite (payloads from 500 kg to 2 tons)  up to low Earth orbit (LEO)

4.Liquid Rocket Jet Engine 

  • This rocket engine used liquid propellant for combustion.
  •  In liquid rocket engine, stored liquid fuels  fuel and oxidizer are injected  into a combustion chamber where they mix and produces product of combustion. Then after, the hot flue gases passes through a nozzle to accelerate. Thrust is produced to lift the rocket.
  • These rocket engines are useful for  Space Shuttle to place human being  in orbit or space station
Liquid-propellant rocket


  • The vortex generator is provide for strong and fast mixing of liquid and oxidizer
  • The actual view of liquid propellant rocket engines . It comprises boost turbo-pump and combustion chamber and nozzle
  •  In the cut section, we can see many nozzles are placed for quick mixing  
  • Cut-section of Combustion Chamber for liquid Rocket engine  

5. Comparison of  solid and  liquid propellant rocket engine


7.CFD Modeling of Rocket Engine


Case Study 1: The Hybrid Liquid Rocket Engine

 CFD Model of Hybrid Rocket Engine

  • Select the appropriate computational domain for analysis of rocket engines
  • CFD modeling of rocket engines involves multi-phase turbulent combustion. To understand the solver setting in CFD solvers,  select appropriate models as per type of fuels.
  • For liquid propellant,
    • Species transport model,: select non-premixed combustion model
    • Turbulence Model: k- e realizable model
    • Spray  Break up Models
    • Multiphase Models: DPM
    • Thermal Radiation model: DO Model
  • Select numerical solution procedures as per basic CFD solver setting
  • Computational Domain:  (a) cooling channel (b combustion model.
  • Boundary Conditions  (a) cooling channel (b) combustion model.
    • Inlet: specify the mass flow rate of oxidizer and fuel, temperature and turbulent quantitates
    • Periodic Boundary: select periodic boundary
    • Outlet: specify pressure outlet
  • Mesh Model and simulation:

    • Meshing of CFD domainwas carried out here using ANSYS mesheing platform
    • Simulation was carried out using ANSYS FLUENT
  •  Results

    • Using the CFD analysis, heat flux ,velocity and temperature can be predicted
    •  The following figure show the heat flux and temperature contours for cooling channel and  combustion model.
  •     Temperature contours in the combustion chamber and nozzle


  • Rocket engine combustion and engine design depend on type of propellants and igniters
  • Liquid rocket engine combustion is complex in space due to very low temperature
  • CFD modeling of rocket engine can be used to study the effect of propellants on development of modern rocket engines


References CFD Modeling 
Research Institute/Laboratory :

8 thoughts on “Rocket Engine Combustion”

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  2. Aerodynamics and propulsion is the study of compressible flows: either around aerodynamic bodies (external flows, aerodynamics or fluid dynamics) or through engines (internal flows or propulsion). Aerodynamics and propulsion is important for numerous aspects of aerospace engineering, such as airplane aerodynamics, helicopter aerodynamics, jet propulsion, rocket propulsion, advanced propulsion, properties of the space environment and many others.

  3. The Gas Dynamics Imaging (GDI) Lab is directed by Professor Mirko Gamba. The GDI Lab research interests and activities mainly focus on laser diagnostics for fluids and reacting flows, low- and high-speed mixing and combustion. They conduct experimental investigation of supersonic combustion in scramjet-type environments, hypersonic impulse facilities, rocket combustion phenomena, development and application of PLIF-based techniques for mixing and thermometry, and turbulent nonpremixed combustion.


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