Combustion Products

The Helmholtz correlations in Sections 2.2 and 2.3 were designed to model hydrogen and oxygen at relatively low temperatures where intermolecular forces cannot be neglected. The hydrogen correlation is accurate within the following limits:^[11]

14 K < T < 1000 K

7 MPa < P < 2000 MPa

The oxygen model is even further restricted:^[12]

54 K < T < 300 K

0 MPa < P < 81 MPa

Propellant temperatures remain in this range as they flow through this SSME’s network of pumps and turbines (refer to Sections 1.1 and 1.2). But temperatures reach up to 3600 K when the propellants mix and react in the pre-burners and main combustion chamber (see Section 1.3). At these high temperatures intermolecular forces may be neglected, and the “ideal gas” approximation may be used. Additionally, during the combustion process diatomic hydrogen and oxygen disassociate and react to form several different species that must be accounted for: $H$, $O$, $OH$, and $H_2O$ (see Section 3.1). Fortunately, NASA has published a wide range of thermodynamic curve fits applicable to these species at temperatures up to 5000 K.^[16] The equations take the following form:

Coefficients are listed in the following format:

The coefficients listed in this table establish correlations for two different temperature ranges. Cells highlighted in red are used for temperatures greater 1000 K. Cells in highlighted in blue are used to model temperatures less than 1000 K. Table 3.4.1 contains the coefficients relevant to this analysis of the SSME:

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