In industrial and propulsion applications, hydrogen-air combustion involves complicated chemical processes and energy exchanges, with radiation playing a major role. Hydrogen gas combusts with air oxygen to produce water vapor and energy. Radiation affects combustion zone temperature and heat transfer during this exchange. The high flame temperatures of hydrogen combustion emit powerful, broad-spectrum radiation. These emissions, from UV to infrared wavelengths, drastically affect system heat transport, combustion efficiency, and pollutant production.

This time, we are simulating a 3D combustion chamber, hosting hydrogen-air combustion considering radiation effects and involving pollutants like Nox production. We have received help from the reference paper entitled “Comparative analysis of hydrogen/air combustion CFD-modeling for 3D and 2D computational domain of micro-cylindrical combustor [1]”.

• Reference [1]: Pashchenko, Dmitry. “Comparative analysis of hydrogen/air combustion CFD-modeling for 3D and 2D computational domain of micro-cylindrical combustor.” International Journal of Hydrogen Energy49 (2017): 29545-29556.
• Reference [2]: Jiaqiang, E., et al. “Effects of inlet pressure on wall temperature and exergy efficiency of the micro-cylindrical combustor with a step.” Applied Energy175 (2016): 337-345.

Figure 1: Schematic diagram of the micro-cylindrical combustor [2]

Simulation Process

The 3D combustion chamber is designed using Design Modeler software in a way that can generate a structured grid later. This is why it consists of 26 separate parts. This results in a fine, high-quality mesh grid that is established at 164160 cells. Both the geometry and grid are shown. The species Transport model is activated to simulate volumetric reactions produced through the combustion of Hydrogen and air. Generally, 19 reactions take place subsequently. One produces the reactants the next reaction and this cycle goes on. Due to the drastic increase in temperature, P1 radiation model is employed to capture radiative thermal effects. Notably, Nox formation due to high temperature inside the chamber is considered.

Figure 2: The computational domain of combustion chamber

Figure 3: Structured Grid over The computational domain of combustion chamber

Post-processing

The cylindrical combustor shows different H2O mass fraction patterns according to the hydrogen-air combustion simulation. The contour map shows entire reaction zones where hydrogen-oxygen combustion reaches optimum efficiency at the downstream section of the combustor, characterized by strong red coloring as a signal for peak water vapor concentration. With mass fraction values ranging from 0.000 to maximum concentration, the slow change from dark to light regions along the combustor length shows a gradual growth of H2O. This spatial distribution pattern confirms that the species transport model well captures the volumetric reaction progression during the 19-step chemical mechanism.

Figure 4: a) H2o b) O mass fraction after Hydrogen-air Combustion Considering Radiation 3D CFD Simulation

Crucially important understanding of the combustion flow dynamics comes from the streamline visualization displayed with H2O2 mass fraction contours. Strong axial momentum with little radial dispersion of the parallel streamlines ensures best residence time for reaction completion. H2O2 intermediate species evolution across the reaction path appears in the color gradient along these streamlines, which moves from red-orange at the inlet to green-yellow at the outflow. Particularly in areas where temperature-dependent reaction rates affect species conversion and NOx generation mechanisms, this pattern validates the capacity of the P1 radiation model to capture thermal-chemical coupling effects.

Figure 5: Streamlines colored by H2o2 mass fraction in Hydrogen-air Combustion Considering Radiation 3D CFD Simulation