Starting Characteristics of a Micro Gas Turbine Engine at Different Loading Conditions

Abstract

Gas turbines offer a more efficient alternative for power generation using fuel derived from waste. They have lower emissions, higher power-to-weight ratio, a smaller footprint, lower emissions, higher reliability and can be used with a wide range of fuels. These qualities make them a lucrative alternative to other conventional power generation methods, especially for distributed power (electricity) generation and supply system applications. In practice, the electrical load profile varies with time, causing the gas turbine to operate at loading conditions other its design point, or better known as off-design conditions. Operation of a gas turbine engine at off-design conditions requires in-depth analysis, especially during starting and load variations when connected to the grid, where transients may lead to instability issues if not regulated appropriately. This analysis is required to design necessary control schedules and put in place corrective actions in case of an instability. In the current work, a micro gas turbine (turbojet) engine is tested at two different loading conditions. The engine is instrumented with pressure, temperature and speed sensors at different locations in the engine. The load on the engine is increased by reducing the nozzle exit area. The objective of the current work is to study both the steady-state and transient operation of the engine, comparing its performance with the baseline engine. Under the first loading condition, the engine running line on the compressor map shifted toward the surge line. Also, the turbine pressure ratio decreased and the turbine entry temperature increased. At the second loading condition, the engine failed to start. At this loading condition, the turbine inlet temperature exceeded safe limits before the engine reached the required speed for a successful start. This failed start is attributed to the reduction in turbine pressure ratio. Under this loading condition, the turbine pressure ratio was not enough to accelerate the rotor speed to the desired speed. The control system continued increasing the fuel flow to facilitate the rotor speed to reach the desired starting speed. This resulted in high fuel flow rates resulting in a very high turbine inlet temperature.