An initial step in the experimental characterization of ultra-lean hydrogen/air turbulent spherical flames for internal combustion engine applications
Résumé
Kick-starting the decarbonization of the heavy-duty transport sector is vital to slowdown
global warming. The use of green e-fuel such as hydrogen for spark ignition engine applications
is currently a promising solution. In order to mitigate pollutant emissions, these engines are
designed to operate with low volumetric hydrogen content. However, under these conditions, the
flame propagation is subject to intrinsic instabilities. Very few studies characterize ultra-lean
premixed turbulent flame propagation, especially due to a lack of unambiguous definitions of
hydrogen combustion fundamental properties such as laminar flame thickness and speed. To the
best of the authors’ knowledge, the first turbulent flame speed measurements are presented for
ultra-lean hydrogen/air mixtures, under spark ignition engine conditions. Literature correlations
considering important turbulent combustion parameters were appraised at engine-like conditions
(high pressure and temperature). The results shows that turbulent flame speed increases with
increasing volumic hydrogen content, pressure and turbulence intensity. A correlation taking
into account preferential diffusion effect, dimensionless Karlovitz and Damkohler numbers was
validated on present¨ experiments and literature datasets. As a matter of fact, including the
interaction of the multi-scale turbulent vortex with the flame front is important in order to characterize
the propagation of such thermo-diffusionally unstable turbulent flames. The conclusions
of this work are relevant to the modeling of ultra-lean turbulent premixed hydrogen/air flames
and thus of practical necessity.