gsphelp  Combustion process

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gsphelp  Combustion process

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The combustion heat release is calculated from the fuel flow and fuel properties. Fuel properties can be specified in terms of a fuel type and H/C ratios and lower heating values. If desired, the fuel composition can be specified instead, composed of a number of predefined species. This option is to allow simulations of systems using alternative fuels such as gasified bio-mass.

Design fuel can be specified separately (from the off-design fuel) to allow maintaining a reference (design) fuel for calculating fuel effects.

Instead of fuel flow, also combustor exit total temperature of combustor exit fuel-air ratio can be user specified to determine the combustor operating point. In that case, fuel flow is calculated. After selecting the appropriate option in the Design tab sheet, GSP works with either fuel flow, exit temperature (or stator outlet temperature, SOT) or fuel-air ratio, both design and off-design. Specifying exit temperature for example is very convenient if calculations with constant (i.e. maximum) turbine entry temperature levels are needed.

Off-design fuel flow (or exit temperature or fuel-air ratio) is specified with control components such as the manual fuel control.

 

For the design point, specify the design combustion efficiency (ratio of effective heat release and 100% combustion theoretical heat release). During off-design the combustion efficiency is determined as user specified or from a map. For a primary combustor, use the map option with combustion efficiency as a function of temperature rise dT and pressure level in terms of d. For an afterburner, use the afterburner efficiency maps with three 2-dim maps (effects of relative (to design values) fuel air ratio, nominal flow Mach number and pressure).

 

The combustion process is calculated using gas and fuel composition data and the equations for chemical equilibrium, meaning that dissociation effects (CO2|CO and H2O|OH) are accounted for.

 

Note that the calculation of delta enthalpy, dH, over the combustor has not much meaning as the composition changes (each individual specie in the gas model is having another temperature at which the H equals zero). Even if all H zero temperature would be equal, dH still has not much meaning in a component like a combustor with detailed/chemical gas models, since both mass and composition changes. Conservation of energy is maintained including a variety of chemical reaction enthalpies. Of course, for an idea of dH that would be used for hand calculation, one could define a calculated column like cp3*(TT4-TT3).