Development of Advanced Models for the Design of a New Micro Gas Turbine Concept

During the past 60 years, the gas turbine engine has continuously increased its importance as prime mover, converting thermal energy into mechanical power. With the enormous improvements in power output and efficiency, the range of applications of this relatively young technology has steadily grown. Major application areas now include aero engines, large heavy duty gas turbines for electric power generation and marine propulsion. Gas turbines are particularly useful if high power levels are required and weight and size must be kept minimal at the same time.

  • A recent trend is the application of micro gas turbines for small‐scale power generation up to 300‐400kW. However, significant challenges (in terms of efficiency, operating costs and environmental issues) still remain in order to make micro turbines competitive in relation to existing concepts. Gas turbine thermal efficiency to a large extent depends on losses resulting from flow leakage, thermal losses and friction. These losses become more dominant when a gas turbine is down‐scaled in terms of size and power, due to blade tip clearance and volume‐surface ratio scale effects. Manufacturing geometrical tolerance limitations inhibit solutions to reduce tip leakage losses for example. Moreover, when decreasing size (which leads to lower Reynolds number) viscous friction losses become larger in conventional turbo machinery. As a result, there is a fundamental limitation to efficiency of micro turbines with a conventional configuration.

By following an unconventional approach, MTT has developed a concept that is not suffering from all above‐mentioned scale‐effects and which is focused on 2 businesses: micro cogeneration (micro CHP) and combined APU/parking heater (CAP).

The key feature is a monolithic rotor. Basically, the turbine comprises of a single rotor including a centrifugal compressor, a rotating combustion chamber and reaction turbine. With the rotating combustor, the compressor does not have a diffuser and the turbine does not have stator vanes. Consequently: leakage and friction losses are eliminated, noise level is reduced due to the absence of stator vanes and effects of deviating flow‐blade angles at off‐design conditions are minimized. In the baseline configuration, a single stage compressor is used. For power output in the range of 1‐10 kW, this means a 60‐80 mm diameter rotor (and eventually even smaller), spinning at rotational speeds up to 110,000 rpm. Without a compressor diffuser, the cycle pressure ratio is limited. As a consequence, the baseline configuration thermal efficiency is limited to approximately 10‐12%; this opens many opportunities for applications in combined heat & power generation.

Next to the development of the baseline configuration, concepts with increased efficiency are being studied and developed, such as an advanced MTT multi‐stage compressor and a recuperated cycle concept, recovering exhaust gas heat. Thermodynamic studies indicate that 2‐stage compression will provide cycle pressure ratios up to 6, resulting in the thermal efficiency rising up to 23%. With more compressor stages and recuperation, efficiency can be further increased to significantly higher levels.

Objective

Objectives of the work are to design a compressor which is optimized in the terms of aerodynamics, cycle thermodynamics, structural design, life and life cycle costs. Thus, the project requires scientific research in thermodynamic modeling aerodynamics, heat transfer, aerodynamic design and optimization of rotating components.