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Navier Stokes with chemical reaction

  1. Jun 6, 2008 #1
    I wasn't sure whether to put this in Aerospace, but decided on physics in the end.

    1.) How do you factor a chemical reaction into the solution for the Navier Stokes equations? More precisely, how can you include the affects of a heat absorbing (endothermic), or heat releasing (exothermic) chemical reaction going in within the flow field? The main thing I have in mind is combustion reactions that occur in jet engines, which are of course exothermic.

    My thoughts were that you would first have to calculate the enthalpy of combustion of the fuel. Then the amount of heat being released is related to the reaction rate, which depends on pressure, and density of air/fuel at a given point (Maybe even "concentration" is a better word). But then in turn, the amount of heat being released would affect the thermal expansion of the gas, and hence the pressure at that point, which again would change the reaction rate and amount of heat being released...etc... until maybe it reaches some kind of equilibrium?

    I was also thinking that you would have to use scalar fields of the form f(x,t) for reaction rate and temperature. Would this be accurate?

    2.) A related question - kerosene is made up of a whole mixture of hydrocarbons, and other things.

    i. where can I find a list of the exact chemical compostion of kerosene? (I believe it may come in different 'grades' or classes, like A1, A2.)

    ii. can you consider kerosene to be a uniform mixture of its constituent compounds, and therefore asign to it an overall enthalpy of combustion, which is like an average for all the constituents?

    I'm having alot of trouble finding information on any of these things, so if anyone knows then please help me out. (Number 1 is the main concern, but though I might as well drop number 2 in there too :) )

    Appreciate any help, regards, Joe
  2. jcsd
  3. Jun 6, 2008 #2
    Can't help with number 1 but Kerosene is also called No. 1 distillate. During the refining of crude oil the fraction obtained after gasoline is a light distillate called kerosene.

    The API gravity for No. 1 oil is between 40 and 44. this is a low sulfur oil with about 135,000 btu's per gallon. The carbon and hydrogen content of 40 API gravity oil is

    Specific gravity: .8251

    % carbon: 85.93

    % Hydrogen: 13.07

    % noncombustibles: 1
  4. Jun 6, 2008 #3


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    Staff: Mentor

    For part 1, the energy absorbed/released would be applied in the heat source of the energy equation. The continuity equation would have to account for the destruction of the fuel and oxidizer and the creation of combustion species, and similar for the momentum equation.

    I've not done NS for combustion systems however.
  5. Jun 9, 2008 #4

    Andy Resnick

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    You will have many coupled N-S type equations:

    1) the conservation of mass, for each species, including sources and sinks via the chemical reactions
    2) the conservation of momentum equations for each species, including diffusion via concentration gradients in the body force term.
    3) the conservation of energy equations for each species, taking into account the thermodynamics of all the chemical reactions.

    There should be some simplifications out there- I worked with combustion folks in the past- but I forget the details.
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