Session: 04-02: Flashback and Blowoff

Paper Number: 82601

82601 - Modeling of Flashback With Different Blends of CH4 and H2 by Using Finite Rate Chemistry With Large Eddy Simulation 

Due to its clean combustion characteristics, hydrogen fuel is gaining attention in power generation. New designs of gas turbine engines are explored by blending with the increasing amount of hydrogen in natural gas. Adding H2 increases the probability of flashback and often is one of the main constraints in using high H2 blends in premixed combustors. There are several mechanisms of flashback like boundary layer flashback, combustion induced vortex break down, turbulence in the flow, fluctuations in equivalence ratio, etc.  Semi-empirical models, based on non-dimensional numbers and flame speed, have successfully predicted flashback propensity for a given operating condition. The semi-empirical models are computationally very efficient; however, they lack generality. A typical combustor can have multiple flashback mechanisms. The relative importance of one vs other mechanisms can change with a change in the combustor design or even with a change in the operating conditions for the same combustor. Since modeling of flashback requires accurate modeling of highly transient chemistry phenomena along with the impact of heat loss on chemistry, a viable detailed chemistry solution is a preferred approach to model flashback.

In this work, we have used a finite rate chemistry model to predict flashback in a turbulent premixed combustor. The configuration used is a swirl stabilized combustor (SimVal) from National Energy Technology Laboratory. The current computations are done with Finite Rate Chemistry (FRC) and Large Eddy Simulations (LES). Simulations are carried out for a varied percentage of CH4/H2 blends, ranging from 0% H2 to 100% H2 at a fixed equivalence ratio and inlet mass flow. As the percentage of H2 is increased in the fuel, flame speed also increases. With this, the propensity of flashback also increases. A 28-species reduced mechanism is developed for CH4/H2 blend flames to keep the simulations computationally tractable.  The simulations with the reduced mechanism are performed by considering non-adiabatic effects from heat loss near the walls and multi-component property considerations. This improves the accuracy of the FRC-LES simulations to capture the onset of boundary layer flashback towards the inlet. The simulations from FRC-LES suggest a fine mesh in the boundary layer for an accurate prediction that makes the simulations expensive. Therefore, an Adaptive Mesh Refinement (AMR) has been used for different CH4/H2 blends to accurately model the flashback without any loss in generality as the AMR criteria used here are applicable for a wide range of conditions. The FRC-based solution strategy proposed in this work provides a framework to model flashback for different blends without any case-specific tuning.

Presenting Author: Ishan Verma Ansys

Presenting Author Biography: Ishan Verma is based in Pune, India, and has been with Ansys for 8+ years. He is a Senior R&D Engineer in the Application Development team within the Fluids Development group. He has got his Master's Degree from IIT Delhi in Energy. For the past years, Ishan has worked in Gas Turbine Combustion, IC Engines, Spray Systems, Emission Control, and High-Speed Flows. He has actively worked with OEM teams from GE, Honeywell, Pratt & Whitney, Ferrari, Bosch, etc., and delivered high-value CFD solutions for engineering configurations. His hobbies include cycling, hiking, and traveling different regions of the world.

Authors:

Ishan Verma Ansys
Rakesh Yadav Ansys Inc
Naseem Ansari Ansys Inc
Stefano Orsino Ansys Inc.
Shaoping Li Ansys Inc
Pravin Nakod Ansys Inc