Session: 04-31: High Hydrogen III

Paper Number: 82111

82111 - Stabilization of Low-NOx Hydrogen Flames on a Dual-Swirl Coaxial Injector 

The growing interest in ecological transition has put hydrogen in the spotlight as a potential fuel to reduce the carbon footprint of numerous industries using combustion, among which the aeronautical and the energy generation sectors. However, the transition to hydrogen creates many challenges. The first challenge is to stabilize flames despite the unique combustion properties of hydrogen compared to conventional fuels. Then hydrogen combustion poses the risk of increasing other types of non-carbon pollution, namely nitrogen oxide (NO_x) pollution, due to the higher combustion temperature of hydrogen. In addition, the high flammability of hydrogen poses an increased risk of flashback in premixed configurations commonly used to generate low-NO_x flames. Thus, the search for a low-NO_x strategy for hydrogen combustion is developing, and several technologies are being investigated. Among these technologies, we consider here a double swirl coaxial injector operated in non-premixed conditions. This is a likely solution for safe low-NO_x hydrogen combustion thanks to its potential for high strain rate flow and enhanced mixing. The injector, housed in a square cross-section combustion chamber, is made of two coaxial channels. Hydrogen is injected into the central channel, and air is injected into the outer channel as the oxidizer. The inner channel is equipped with swirl vanes and the outer channel flow is swirled thanks to axial and tangential inlets. This defines two swirl numbers that can be independently controlled and contributes to the generation of multiple flame fronts that may be present simultaneously or not. Flow conditions then yield varying attached and detached flame structures that affect the thermal and chemical environment of the flame.

A parametric investigation is undertaken to explore the topologies and the associated NO_x emissions of hydrogen flames in this burner at atmospheric pressure. The flame structure is observed using OH* chemiluminescence images collected by an intensified CCD camera equipped with a band-pass filter. Mole fractions of exhaust gas species (NO + NO₂ and O₂) are measured using NDIR gas detectors and a paramagnetic sensor. Finally, the temperature is measured at the chamber wall and exit cross-section. The investigation involves varying the inner swirl number by changing the swirl vanes angle and the outer swirl number through variation of the axial to tangential injection ratio. The momentum flux ratio between the two channels of the injector is also varied by modifying the total air flow rate. This allows the exploration of a wide range of flame structures. The study reveals various stabilizations of hydrogen-air flames on the double swirl injector with five types of flame structures ranging from attached diffusion flames to fully lifted flames. In addition, low-NO_x flames are achieved under high swirl conditions, and hydrogen flames with an emission level under 10 ppm, below that of equivalent methane flames, have been observed.

Presenting Author: Maxime Leroy EM2C Laboratory, CNRS, CentraleSupélec, Université Paris-Saclay

Presenting Author Biography: Maxime Leroy is a research intern working at the EM2C laboratory to complete his Master's degree in Aerospace engineering from Paris-Saclay university and CentraleSupélec.

Authors:

Maxime Leroy EM2C Laboratory, CNRS, CentraleSupélec, Université Paris-Saclay
Clément Mirat EM2C Laboratory, CNRS, CentraleSupélec, Université Paris-Saclay
Antoine Renaud EM2C Laboratory, CNRS, CentraleSupélec, Université Paris-Saclay
Ronan Vicquelin EM2C Laboratory, CNRS, CentraleSupélec, Université Paris-Saclay