11 research outputs found
A comparative study of different reaction models for turbulent methane/hydrogen/air combustion
Reaction modelling of methane/hydrogen combustion has two
important aspects. First, such mixtures may be used in future
in combustion devices like gas turbines and gas engines in the
frame of the demand for efficient energy storage systems,
where the amount of hydrogen in natural gas delivering
systems may vary according to varying hydrogen production
from renewable energies. Second, this can be an important
aspect for safety, as such mixtures may occur in disastrous
situations and calculations may allow the prediction of safety
issues. Modelling of such mixed fuel combustion processes is
non-trivial due to the involved preferential diffusion effects,
coming from the different diffusivities of methane and
hydrogen. In turbulent flame modelling, this topic is of special
interest, as also thermo-diffusive instabilities and local
influence of the local burning velocity near leading edges of
the flame seem to be of importance even for highly turbulent
flames. This numerical work deals therefore with a
comparative study of five different turbulent combustion
models - Bray-Moss-Libby, Linstedt-Vaos (LV), a modified
version LV, Turbulent Flamespeed Closure, and Algebraic
Flame Surface Wrinkling model - to the situation of turbulent
methane/hydrogen/air flames. Validation is done with
extensive experimental data obtained by a low swirl burner in
the group by Cheng. Besides a basic case with pure methane/air, special emphasis is laid on flames with 40 to 100
% hydrogen content by volume. It is shown that for such
methane/hydrogen fuel mixtures common reaction rate models
are not sufficient where the fuel effects are included only via a
laminar flame speed. Instead, a recently proposed reaction
model with the incorporation of an effective Lewis number of
the fuel mixture is found to work rather well. This is of both,
practical as well as theoretical importance, as for the latter it
confirms controversially discussed assumptions of the
influence of preferential diffusion