Fuel pump/compressor
Fuel pump/compressor
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The power required for compressing the fuel for injection into the combustor can be calculated and taken from a user specified shaft. The fuel pump power effect can be separately specified and accounted for in DP and OD simulation mode. Pump/compressor power calculation depends on fuel type, either:
•Incompressible (liquid) fuel flow
(power is pressure delta * volume flow, density needs to be specified)
•Compressible with user specified ETAis
(power is calculated using the appropriate equation for compression power at a user specified isentropic efficiency)
The fuel pump/compressor entry pressure is user specified. The fuel pump/compressor exit pressure is static combustor inlet pressure plus an additional injection overpressure. If static combustor inlet pressure is not available (no entry area (i.e. upstream component exit area) specified ) total is taken instead.
The fuel pump inlet temperature is taken from the Fuel (for DP Design Fuel) tab sheets user specified data.
The fuel pump calculation can be activated/deactivated (using the Account for fuel pump/compressor power check box) and works for both DP and OC calculations. Note that in order to analyse fuel compressor power effects as an OD effect, the Reinitialize model on case type change option in the General | Initialization options needs to be disabled: then run a DP first without Fuel pump active, then follow with OD with Fuel pump active.
Calculation of absolute enthalpy (H) of fuel before (Hfueltank) and after fuel (Hfuelin) compression and output for use in system energy balance calculations:
a)When using Hfueltank for the energy balance, the fuel compression system is included in energy balance system boundary. Fuel compressor power and fuel temperature effects calculation options (Add fuel temperature rise due to compression and Account for fuel pump/compressor power) must be either both active or both inactive for the energy balance to remain consistent.
b)When using Hfuelin, the fuel compression sysem is excluded from energy balance system boundary. The fuel compressor power calculation option must be deactivated.
Note that the energy balance expression can easily be calculated as an output calculated expression. For a simple turboshaft for example as a % of total input heat rate: 100*(W1*H1+Wf*Hfuelin-W9.H9-PWshaft)/(Hv_b*Wf_b))
When the energy balance is closed properly, the result of this expression should be close to 0 (typically less than 0.1 %). For gaseous fuels, compression power and fuel enthalpy rise is calculated using the user specified isentropic fuel compression efficiency. For liquid fuels, fuel compression/punp power is calculated as volume flow rate * dp and the resulting work per kg fuel added as a 'virtual total temperature' of the liquid fuel to account for the energy released as kinetic energy in the fuel jets when exiting the injector and entering the combustor.