Session: 04-49 Emissions V

Paper Number: 102876

102876 - Structure and Nox Emissions of Stratified Hydrogen-Air Flames Stabilized on a Coaxial Injector 

In recent years, the need for low-carbon power has seen hydrogen emerge as a potential fuel to replace conventional hydrocarbons in combustion to limit CO₂ emissions in several sectors, including aeronautics. The challenges posed by hydrogen combustion are similar to the issues of kerosene flames, like nitrogen oxide emissions and flame flashback. On kerosene flames, these challenges were overcome through a variety of combustion chamber concepts, such as lean direct injection, Rich Quick-Mix Lean, or Lean-Premix-Prevaporized. However, the vastly different combustion properties of hydrogen when compared to kerosene, such as its large flammability range, its high adiabatic flame temperature, or its low density make it difficult to use these past concepts to design a hydrogen-powered aircraft engine. However, inspiration can be taken from those concepts to find ways to produce stable low-NO_x hydrogen flames while taking advantage of hydrogen’s unique properties. One such idea is to explore the rich side of the equivalence ratio range, as suggested by RQL combustion. Indeed, a rich premix allows low-NO_x combustion due to the low availability of oxygen and lower flame temperature, and more stable combustion, as the Markstein number of hydrogen goes from negative (the flame accelerates with stretch) in the lean domain to positive (the flame decelerates with stretch) in the rich domain. In addition, the high stretch resistance of hydrogen allows for quick mixing of air to return to globally lean conditions. To investigate whether this concept functions in practice, we use a coaxial injector in which a rich premix of hydrogen and air is injected into the central channel, and air is injected into the annular channel.

The flames are studied under atmospheric pressure. OH* chemiluminescence imaging is used to study the structure of the flame as well as to measure flame length, while mole fractions of exhaust gas species of interest (NO, NO_2, and O₂) are measured using NDIR gas detectors and a paramagnetic sensor. Additional temperature measurements are also made at the chamber exit where the burned gases are sampled. NO_x measurements are performed under varying conditions of rich premix equivalence ratio as well as global equivalence ratio, and attempts are made to link these behaviors to injection parameters and macroscopic parameters such as flame length as previous works such as Peters & Donnerhack (Symp. (Int.) Combust., 1981) have shown a link between NO_x production and flame length. This link is also investigated in the present study, and models for accurate estimation of flame length based on injection parameters are studied.

 

 

 

 

 

 

Presenting Author: Maxime Leroy Université Paris-Saclay

Presenting Author Biography: Maxime Leroy obtained his master's degree in Engineering from Université Paris-Saclay in 2021. He has since been working on hydrogen combustion at EM2C Laboratory and is now a PhD student in collaboration with Safran Tech to study low-NOx hydrogen combustion.

Authors:

Maxime Leroy Université Paris-Saclay
Clément Mirat Université Paris-Saclay
Antoine Renaud Université Paris-Saclay
Stefano Puggelli Safran Tech
Stephan Zurbach Safran Tech
Ronan Vicquelin Université Paris-Saclay