Session: 19-03: Micro Gas Turbines.

Submission Number: 178623

Investigation of the Influence of an Adjustable Air Split Inside a Gas Turbine Combustion Chamber on the Flexibility of Micro Gas Turbine Operation 

Through the vast expansion of renewable energy production and the continuously developing requirements for the existing energy systems, an increased flexibility of the subsystems is needed. With their relatively low exhaust gas emissions, their fast start-up, their high energy density and their flexibility in operation and fuel usage, stationary gas turbines play a unique role in the energy transition. Therefore, this paper investigates how a dynamic adaptation of the air split inside a micro gas turbine combustion chamber enhances the operating range and fuel flexibility of micro gas turbines to adapt to these changing requirements. A shifting of the air split during gas turbine operation, allows for a direct adjustment of the local air fuel ratio in the primary combustion zone and therefore an adaptation of the combustion conditions to the respective boundary conditions. This enables various advantages, ranging from optimized exhaust gas emissions to an enhanced operating range and possible application cases, up to a strongly increased fuel flexibility. Therefore, as a proof-of-concept platform for the air split adaptation, a one stage, jet-stabilized combustion chamber of a MTT EnerTwin micro gas turbine with an electrical output of up to 3 kW_el is investigated. Based on the results of a prior atmospheric measurement campaign, an orifice was designed, which allows for an adjustment of the air split inside the combustion chamber during gas turbine operation. To allow for an orifice design with a maximized effect on the air split - while minimizing its overall pressure loss – additional CFD simulations were carried out. The orifice was then implemented into the combustion chamber and investigated in a gas turbine test rig. It could be shown, that the orifice is able to shift the air split and therefore successfully adjusts the local air fuel ratio. This is also clearly indicated in the influence of the orifice positions on the emissions of the gas turbine. The performance of the orifice is shown for different boundary conditions, including fuel, load and temperature variations. While it could be proven, that the orifice influences the gas turbine operation as designed, the overall air split area has to be adapted to optimize its impact on the gas turbine operation of the MTT EnerTwin. However, the main focus of this investigation was the proof-of-concept of the orifice, which is successfully shown. This investigation is the baseline for the next step, where the orifice will be optimized for a gas turbine system with higher power output, which then will be used as a demonstrator system, with optimized emissions.

Presenting Author: Sebastian Bellaire German Aerospace Center (DLR)

Presenting Author Biography: studied mechanical engineering at TU Kaiserslautern (Germany) in 2021
started in March 2022 at the DLR in Stuttgart (Germany) at the institute of combustion technologies (up to today)

Authors:

Sebastian Bellaire German Aerospace Center (DLR)
Nikhil Shinde German Aerospace Center (DLR)
Jan Zanger German Aerospace Center (DLR)
Hannah Seliger-Ost German Aerospace Center (DLR)
Andreas Huber German Aerospace Center (DLR)