NASA-Library

Initially those 83 substances of the NASA library were used, that are also available with streams of type classical composition.

The new stream type has been introduced to allow the use all substances of the NASA library in Ebsilon. The idea is to avoid the situation that 2000 blank values have to exist on each line. In the case of the NASA fluid, values are only stored for those substances with a concentration of >0.

This stream type now allows to use all substances considered in the equilibrium calculation also in Ebsilon when calculating the chemical equilibrium with Component 134 (Equilibrium reactor (Gibbs)).

The physical properties data for this line type are calculated with the NASA algorithms for ideal gases. Here no phase transitions are considered, neither for water in particular. Therefore care has to be taken that this fluid is only used in areas where all components are gaseous (compliance with this condition is not checked!).

For the sake of a simplified calculation of chemical reactions, the enthalpy zero points in the original library were selected in such a way that the difference of the outlet and inlet substances of the reaction result in the enthalpy of formation; thus, in a manner of speaking, the NCV is contained in the enthalpy. When integrating the library into Ebsilon, however, the distinction between enthalpy and NCV common in Ebsilon was re-introduced, in such a way that the difference of the NASA enthalpy at the current temperature to the NASA enthalpy at T=0°C is displayed in Ebsilon as enthalpy (whereby it has its zero point for all substances at T=0°C). The NASA enthalpy at T=0°C is then displayed as NCV in Ebsilon. Here both negative and positive values occur; what matters is always the difference between inlet and outlet substances.

The usual procedure of Ebsilon to assign an NCV of 0 to the end products of a complete combustion has not been implemented here as intuitively it is not clear what the end product is in each case (because in many cases there are different oxidation stages). Therefore the NASA values have just been retained.

The NASA library also contains the elements C, H, O, N, S, and Cl. Here the data contained in the library refer to mono atomic gases of these elements as they occur at temperatures of several thousand °C or at extremely low pressures (e.g. in interstellar matter). In order to at least approximately support the use as elementary analysis for solid and liquid fuels common in Ebsilon, the following modifications have been made to the NASA library for these elements:

• For “low“ temperatures (<= 1500°C for C, O, N, S, Cl, <=1250°C for H), the cp-coefficients according to FDBR for “Coal (old mode)“ are used
  
•  The cp-coefficients according to NASA are only used at higher temperatures (for C from 1865.511 °C, for H from 4000 °C, for O from 2109 °C, for N from 2030 °C, for S from 2302 ° C, and for Cl from 2311°C)
  
• In the intermediate range, the FDBR polynomials have been extrapolated for C, O, N, S, Cl up to the point where the cp according to FDBR matches the NASA value in order to enable a smooth transition. For H, the cp of the monatomic gas is significantly higher (20 kJ/kgK compared to 2 kJ/kgK in the case of FDBR), so that here there was no intersection and a spline has been used instead, with matching values and the derivatives at the two boundary points. The lower boundary point has been set to 1250°C because the FDBR polynomial decreases above this point, departing further from the NASA value again.
  
• The constants of integration for the enthalpy and the entropy have been adjusted for all ranges (also the NASA high-temperature range of 6000 to 20000 K) in order to enable a smooth transition.
  
• For the entropy, however, the adjustment with FDBR is only correct at a pressure of 1 bar as the entropy at NASA is pressure-dependent (ideal gas!)
  
• For the specific volume and density, NASA provides the values for the ideal gas and therefore the results differ significantly from results for solid substances.