Optimizing the design of a combustion system

Accurate mathematical models play a key role in the design of stable combustion appliances. For his PhD research, Roeland Wildemans investigated and modelled the dynamic behaviour of flames. This new model accurately describes the dynamic behaviour of the flames and requires low computational cost for its simulation. This is of crucial importance when the design of a combustion device is optimized, whereby typically multiple model simulations need to be executed.

Combustion appliances are omnipresent in our daily lives. Well-known examples of combustion devices are boilers, gas turbines or jet engines. In these devices, a fuel is burned to generate heat, which in turn is used to heat buildings, drive engines, or produce electricity. For a long time, carbon-based fuels were the standard, due to its high energy density. However, the combustion of carbon-based fuels contributes significantly to the global warming and causes air pollution. Therefore, it is essential to switch to renewable energy sources. Combustion appliances can be decarbonized by using hydrogen as fuel. Moreover, the production of NOx can be significantly reduced by using so-called lean air-fuel mixtures. However, by using sustainable and lean air-fuel mixtures, the combustion appliances become extremely sensitive to thermo-acoustic instabilities. Accurate mathematical models play a key role in the design of stable combustion appliances.

Thermo-acoustic instabilities

However, by using sustainable and lean air-fuel mixtures, the combustion appliances become extremely sensitive to thermos-acoustic instabilities. These instabilities are the consequence of a complex interplay between the heat-source, e.g., a flame, and the acoustics in the device, and manifest themselves as strong pressure waves that cause noise disturbance. These acoustic vibrations could lead to performance deterioration or even structural damage of the combustion device. Thermo-acoustic instabilities are therefore an undesired phenomenon and cause a severe challenge in the design of sustainable and stable combustion appliances.

Accurate mathematical models

Accurate mathematical models play a key role in the design of stable combustion appliances. These models could be used to assess the stability of the combustion device in an early design stadium and if required to make modifications to the design. These mathematical models consist typically of two parts: a model of the acoustics and a model of the flame. Accurate models of the acoustics are widely available, however, accurate models that describe the nonlinear flame dynamics are missing.

Mathematical model of flames

In his research, Wildemans investigated and modelled the dynamic behaviour of flames. First, by means of experiments he identified the different vibrations produced by the flames. Next, Wildemans used the experimental data in a data-driven method to develop a mathematical model of the nonlinear dynamics of the flames. This new model accurately describes the dynamic behaviour of the flames and requires low computational cost for its simulation. This is of crucial importance when the design of a combustion device is optimized, whereby typically multiple model simulations need to be executed. Finally, an experimental validation study is executed to show that the new flame model provides a good prediction of the behaviour of the combustion appliances, that are characterized by designs with different acoustic features.

Title of PhD thesis: Nonlinear dynamics of intrinsic thermo-acoustic modes. Supervisors: Ines Lopez Arteaga, Philip de Goey and Viktor Kornilov.