The Emissions tab sheet of the combustor component contains the emission models determining NOx, CO, UHC and soot during combustion. When using emission models (instead of None), three options are available:

•Interpolation in ICAO table (or NLR emission model)

Data available from the ICAO emission databank can be entered in a table for interpolation to obtain a rough means to interpolate between combustor operating conditions for NOx, CO, UHC emission index data and Smoke number data. The ICAO table consists of four data sets of emission indices for take-off, climb out, approach and idle.

•Semi-empirical ratio- or direct prediction method

For this method emission indices in the design point are used to predict the emission indices in off-design conditions ('P3T3 models').

Note: a prediction method for UHC is not yet available, therefore the EIuhc will always be equal to 0 for this option

•Multi-reactor combustion model [4] (available is emission component library only)

A combustion chamber model is built by dividing the combustion chamber liner volume into an array of reactors. In each reactor 4 flows can enter: the flow from the previous reactor, an oxidant flow coming from outside the liner, the fuel flow, and a flow of water/steam. These 4 flows are assumed to mix instantaneously and reach equilibrium at the reactor exit.

In general, two types of emission formation are discerned: instantaneous formation in a flame and gradual formation throughout the combustion chamber. The instantaneously formed emissions are added to the total amount of emissions present so far. The gradual formation determines emission formation rate equations. The (equilibrium) temperature, composition and the actual emission concentration at each reactor exit are used to calculate the emission formation rates, which are numerically integrated.

Four mechanisms of NOx formation are modelled: prompt NOx, fuel NOx, thermal NOx and NOx formation by the N2O mechanism. The amounts of prompt NOx and fuel NOx are calculated using empirical equations and supposed to be formed instantaneously in flames. Thermal NOx and NOx formed by the N2O mechanism are assumed to be formed throughout the combustion chamber.

For CO emmissions it is assumed that the fuel reacts instantaneously to CO (and H2O), and is subsequently (gradually) oxidised to CO2 by one chemical reaction.

For UHC emmissions, the fuel is converted to an amount of jet fuel or methane, depending on the fuel used. Both the jet fuel and methane are (partially) oxidised in the subsequent part of the combustion chamber.

For smoke (soot), the assumption is made that the soot particles are spherical. An empirical equation is used to predict formation, while kinetic-type expressions are used to calculate the smoke oxidation.

The last two emission models calculate emission indices (EI) relative to a user defined design point reference EI value, making GSP particularly valuable for emission sensitivity analysis.

Note: Using the combustor component for emission calculations requires thorough knowledge on the underlying theory and equations of the options applied.