Session: 04-28 Emissions Hydrogen/Ammonia I

Paper Number: 153396

Effect of H2-Air Premixing Characteristics on NOx Emissions in Microinjector Systems 

With a push toward decarbonization, hydrogen has emerged as a popular carbon-free energy carrier with a strong focus on designing and modifying combustion systems to support its burning. With its high flame speed and flashback tendencies, jet flames have emerged as a dominant flame holding choice for pure hydrogen flames leading to the use of micromixer type injectors for dry, low-NOx next generation systems. These injectors are simple tubes with air flow, with hydrogen injected as a jet-in-crossflow to enhance mixing. Important geometrical features include the injection location upstream of the tube exit (controls degree of mixing) as well as injection strategies (different geometrical ways in which fuel is injected). These features have strong impacts on the mixing length for a perfectly premixed hydrogen-air mixture which can have significant impacts on NOx emissions. The objective of this paper is to bridge fundamental research with practical design. The methodology is multifaceted, including canonical research evaluation and distillation on the subject, new research and practical distillation of fundamentals into actionable design tools. The primary focus was on the fundamental designs, which impact NOx emissions and flashback propensity. In the new research section of the study, six different configurations with varying lengths of the premixing section were numerically analyzed to understand their mixing properties and estimate NOx emissions. Three-dimensional steady RANS simulations were performed for the microinjector configurations and statistics from these simulations were assessed to compare the relative performance of these microinjector configurations across different mixing lengths. The local composition profile resulting at the end of the mixing section for each configuration was then used in a one-dimensional flame model to simulate the NOx emissions. A key input here is the degree of mixing in the fuel-air mixture as well as a measure of the combustor length, through a residence time. Interestingly, cross-section profile mixedness rate of change with axial location (as well as mixedness itself) can vary significantly with design. The results of these studies shed light on the effect of geometrical designs of the micromixer tube and combustor residence time on NOx emissions as well as providing potential methods for flashback predictions. Using this framework, a reduced order model and subsequent design tool can be developed to predict NOx levels for different micromixer design configurations. 

Presenting Author: Guru Charan Ganesh Georgia Institute of Technology

Presenting Author Biography: Guru Charan is a second year PhD student at Georgia Tech and primarily works on combustion simulations and modeling.

Authors:

Guru Charan Ganesh Georgia Institute of Technology
Hari Priya Rajagopalan Georgia Institute of Technology
Jim Harper EPRI
Vishal Acharya Georgia Institute of Technology
David Noble EPRI