2 Literature review on gas turbine performance

Figure 3: Ambient Temperature Power Correction Factor Curve (Petchers, 2002)

Figure 4: Effect of ambient temperature and air to fuel ratio on thermal efficiency (Rahman, et al., 2011)

2.1.2 Ambient Pressure

Ambient pressure is a site dependent parameter and it changes with the elevation. With the increases of the elevation, the density of the air reduces, thus ambient pressure reduces. As results of that mass flow rate, fuel rate and the power output of the gas turbine reduce nearly by 3.5% for each 1000 feet (305m) of elevation above the sea level (Petchers, 2002). Figure 5 describes how the power output of the gas turbine changes with the elevation. The Y-axis of the figure 5 represents the ratio between power output at any elevation and power output at reference elevation. This ratio is defined as power output correction factor. The unit is defined as HorsePower_any/HorsePower_reference (HP/HP).The reference elevation of the curve in the figure 5 is 0 feet (sea level). According to the curve, the output power correction factor for the 0 feet is 1 HP/HP and it reduces with the elevation inclination.

Figure 5: Representative Altitude Power Correction Factor Curve

2.1.3 Humidity

The atomic mass of the H₂O is less than N₂ and O₂. Due to that reason mass of the humid air is less than the mass of the dry air (same volume). Therefore the humid air has less density than the dry air. As a result of low density air, the amount of dry air mass entering into the gas turbine reduces. Thus the performance of the gas turbine reduces.
Humid air exists in gas turbines by several means; ambient air is a one mode to does that. Normally the ambient air contains certain amount of moisture. Therefore the humid air directly goes through the gas turbine by means of the ambient air. Water or steam injection to reduce NO_x is another way to increase the humidity level in the gas turbine (Brooks, 2005).