Concurrent design of a micro-turbine incorporating model based design

Over the last two decades, energy generation demand has been increasing significantly, particularly because of environmental policies, enhanced regulations to enforce ultra-low or zero emission systems, mobilisation and technological improvements. Consequently, new energy generation and co-generation systems are hot topics to provide alternative, more efficient, cheap and easily accessible heat and power. One of the uprising and promising source to meet these needs of the industry is micro-turbines. Especially when they are used in combined cycle processes, they play a very important role in power generations with production capability of the highest efficiency. In this thesis, parametric study model for a small-scale micro-turbine system to analyse the behaviour for aimed electricity and heat generation values in order to reach out to a successful design is accomplished. Within the expected 1 – 1.5 bar pressure difference inside the system, 0.1 – 0.5 kg/s mass flow range is predicted with 800 – 1300 K turbine inlet temperature to provide required power outcome for different RPM scenarios and expected energy generation. At the end, an optimum system operation to serve households and potential other industries with a nominal energy generation of 14 kW for heat and electricity is achieved. Design and development of the micro-turbine system is conducted by utilizing multidisciplinary concurrent engineering facilitating mainly initial P&ID diagram drafting for system constitution with following model based design. A mathematical model within a model based software environment is used to study system dynamics within the entire operating envelope. This also delivered the reverse information flow to fuzzy front-end of the system spanning the concurrent environment. In other words, during all the analyses and development, model-based design within the V-cycle is taken advantage of. Since gas turbines are quite complex systems and highly non-linear in overall performance behaviours, each of the system component is going to modelled independently to be gathered at the end. The models are developed virtually in MATLAB/Simulink which is an advanced dynamic multidisciplinary simulation environment. Modelling approach starts with the mathematical models development for each micro-turbine system individually based on the thermodynamic and physical laws, based on Brayton cycle. The design order of main components follow compressor, combustor and turbine. Each independent model is compared with matching ones throughout concurrent engineering process to ensure the coherency between components. After these main parts are finalised and made sure to meet the design goals, other sections of recuperator and heat exchanger models are developed. During the each development phase, validation analyses are made to ensure the correct operation. After code development of each model, entire system is modeled in Simulink Simscape to run entire system together for further analyses and simulation on design, off-design and transient cases. For each component model, in-house MATLAB programs are developed. Both on compressor and turbine sections, industrial products with their data are used. For compressor, Garrett GTX4294R centrifugal type is chosen with the help of initial mass flow and pressure requirement estimations to meet the design goals. For turbine, axial type preliminary version of a map is read and scaled according to the design goals. Both maps are processed via industrial GasTurb Smooth programs. The developed programs are capable of simulating any compressor / turbine maps that are processed with GasTurb. During the solution process of both compressor and turbine, Newton-Raphson iterative method combined with general minimal residual and adaptive robust numerical differentiation methods are taken advantage of. Additionally, these methods enable to reach transient steady-state solutions for the system. Combustor design is established with the help of 1-D Network Model that enables to obtain deeper performance analyses of geometry variations, cooling geometry effects and general efficiency of combustion. With chosen most relevant design parameters, an optimum combustor design with the lowest total pressure loss and maximum efficiency is made, following by its modelling. Rest of the components are modelled with simple physical laws. By conversion of all models into Simulink, faster analyses and simulations are possible with further capability of running real-time simulations thanks to all combined methods. All these factors enable to achieve a very realistic micro-turbine system at the end that is aimed to be less expensive, easy to be produced and simple to be used in automative, aerospace and other industries. The system consists of an centrifugal compressor and a turbine, connected via a single shaft, tubular combustor together with recuperator, alternator, and an exhaust with a heat exchanger.