A gas turbine combustion chamber modeling by physical model

The validity of the gas turbine unit model largely depends on the accuracy of the flue gas temperature value calculation at the gas turbine inlet (TIT). This temperature is determined by the maximum combustion temperature. In variable running mode, the temperature value is regulated by changing the ratio of air and fuel at the inlet to the combustion chamber. The paper presents a model of a gas turbine combustion chamber using Modelica, an object-oriented language for modeling complex physical systems with the aim of determining the temperature of combustion flue gases, specific heat capacity, enthalpy, and flue gas composition at different gas turbine loads.

Improved CFD Predictions of Pyrolysis Oil Combustion Using Advanced Spray Measurements and Numerical Models

In search of an economical and environmentally friendly manner of power generation the industry is forced to find fuels which can replace conventional fossil fuels. During the last years this has led to significant developments in the production of alternative fuels, whereby these fuels became a more reliable and more efficient source of energy. Fast pyrolysis oil (FPO) is considered as a promising example of one of the alternative fuels. This research focuses on the application of FPO in a gas turbine combustion chamber. For the OPRA OP16 gas turbine, a numerical approach using advanced CFD simulations has been applied to a real scale gas turbine combustor. The simulations are supported by full-scale combustor tests and atomizer spray experiments. Hereby it has been shown numerically and experimentally that the gas turbine combustion chamber can operate on FPO in the 30–100% load range. The droplet Sauter Mean Diameter (SMD) has been investigated by means of a Particle Droplet Image Analysis to visualize the sprays in the near field of the atomizer. The effects of the spray pattern are of key importance to the flame structure in the gas turbine combustion chamber. Therefore the results from this dedicated test experiment have been used as input for dedicated CFD simulations. A dedicated combustion model of fast pyrolysis oil has been developed for the OpenFOAM code, considering both the evaporation of the oil and the burnout of the char. In the simulations the gas turbine electrical load, the cone angle and the droplet SMD of the spray were varied. These simulations provide a detailed insight and description on the evaporation of the pyrolysis oil and the flame characteristics in the low calorific fuel combustor of OPRA’s OP16.

Towards Reduced Order Models of Small-Scale Acoustically Significant Components in Gas Turbine Combustion Chambers

Gas turbine combustion chambers contain numerous small-scale features that help to dampen acoustic waves and alter the acoustic mode shapes. This damping helps to alleviate problems such as thermoacoustic instabilities. During computational fluid dynamics simulations (CFD) of combustion chambers, these small-scale features are often neglected as the corresponding increase in the mesh cell count augments significantly the cost of simulation while the small physical size of these cells can present problems for the stability of the solver. In problems where acoustics are prevalent and critical to the validity of the simulation, the neglected small-scale features and the associated reduction in overall acoustic damping can cause problems with spurious, non-physical noise and prevents accurate simulation of transients and limit cycle oscillations. Low-order dynamical systems (LODS) and artificial neural networks (ANNs) are proposed and tested in their ability to represent a simple two-dimensional acoustically forced simulation of an orifice at multiple frequencies. These models were built using compressible CFD, using OpenFOAM, of an orifice placed between two ducts. The acoustic impedance of the orifice has been computed using the multi-microphone method and compared to a commonly used analytical model. Following this, the flow field downstream of the orifice has been modelled using both a LODS and ANN model. Both methods have shown the ability to closely represent the simulated dynamical flows at much lower computational cost than the original CFD simulation. This work opens the possibility of models that can dynamically predict the flow through, for instance, acoustic liners, dilution ports and fuel injectors in real engines during thermoacoustic instabilities without having to mesh and simulate these small-scale features directly. Such models may also assist in the accurate simulation of flame quenching due to cooling flows or the design of effusion cooled aerodynamic surfaces such as nozzle guide vanes (NGVs) and turbine blades.

Investigations of the Emission Characteristics of a Dual-Fuel Gas Turbine Combustion Chamber Operating Simultaneously on Liquid and Gaseous Fuels

This study is dedicated to investigations of the working process in a dual-fuel low-emission combustion chamber for a floating vessel’s gas turbine. As the object of the research, a low-emission gas turbine combustion chamber with partial premixing of fuel and air inside the outer and inner radial-axial swirls was chosen. The method of the research is based on the numerical solution of the system of differential equations which represent the physical process of mass and energy conservation and transformations and species transport for a multi-component chemically reactive turbulent system, considering nitrogen oxides formation and a discrete ordinates model of radiation. The chemistry kinetics is presented by the 6-step mechanism of combustion. Seven fuel supply operating modes, varying from 100% gaseous fuel to 100% liquid fuel, have been analysed. This analysis has revealed the possibility of the application of computational fluid dynamics for problems of dual-fuel combustion chambers for the design of a floating vessel’s gas turbine. Moreover, the study has shown the possibility of working in different transitional gaseous and liquid fuel supply modes, as they satisfy modern ecological requirements. The dependencies of the averaged temperature, NO, and CO concentrations along the length of the low-emission gas turbine combustion chamber for different cases of fuel supply are presented. Depending on the different operating modes, the calculated emission of nitrogen oxides NO and carbon monoxide CO at the outlet cross-section of a flame tube are different, but, they lie in the ranges of 31‒50 and 23‒24 mg/nm3 on the peak of 100% liquid fuel supply mode. At operating modes where a gaseous fuel supply prevails, nitrogen oxide NO and carbon monoxide CO emissions lie in the ranges of 1.2‒4.0 and 0.04‒18 mg/nm3 respectively.