Thermal diffusion, exhaust gas recirculation and blending effects on lean premixed hydrogen flames

Proceedings of the Combustion Institute, vol. 40, pp. 105429

Abstract

Thermodiffusively-unstable lean premixed hydrogen flames are investigated using two-dimensional direct numerical simulation employing finite-rate chemical kinetics. Three databases are generated focussing on the inclusion of the Soret effect , the recirculation of exhaust gas , and blending with methane. A simple rescaling of a classic thermal diffusion model is presented and shown to mimic multicomponent diffusion with very low computational cost and little-to-no loss in accuracy. It is also shown that a previously developed model for mean local flame speeds in lean premixed hydrogen flames [1] can still be used provided Soret effects are taken into account in one-dimensional calculations. The addition of exhaust gas to the unburned mixture is found to enhance thermodiffusive instability; the primary mechanism for this was shown to be the highly-efficient third-body nature of water, with the reduction of adiabatic flame temperature a second-order effect. Again, the existing mean local flame speed model proved sufficient. Finally, blending with methane was found to reduce the thermodiffusive response of the flame, more so than the existing model suggests, despite adjustment of the fuel Lewis number; an adapted model is presented to account for this.

Authors 4

1. T.L. Howarth corresponding Aachen Institute for Combustion Technology

   Newcastle University · RWTH Aachen University

   Affiliation as printed

   Institute for Combustion Technology, RWTH Aachen University, Aachen, 52056, Germany

   School of Engineering, Newcastle University, Newcastle-Upon-Tyne, NE1 7RU, UK

2. Marc Day

   National Laboratory of the Rockies

   Affiliation as printed

   Computational Science Center, National Renewable Energy Laboratory, Golden, CO 80401–3305, USA

3. Heinz G. Pitsch Aachen Institute for Combustion Technology

   RWTH Aachen University

   Affiliation as printed

   Institute for Combustion Technology, RWTH Aachen University, Aachen, 52056, Germany

4. Andrew J. Aspden

   Newcastle University

   Affiliation as printed

   School of Engineering, Newcastle University, Newcastle-Upon-Tyne, NE1 7RU, UK