Direct numerical simulation of autoiginition of a hydrogen jet in a preheated cross flow

Autoignition of a nitrogen-diluted hydrogen mixture issuing from a round nozzle into a cross-flowing turbulent stream of preheated air flowing in a channel at a friction Reynolds number Re_τ = 180 is investigated via 3-D direct numerical simulations (DNS) at two crossflow stream temperatures (930 and 950 K). Three-dimensional visualizations of the JICF reveal a complicated flow structure characterized by a variety of coherent vortical structures resulting from the boundary layers near the walls and evolving from the jet instabilities. The mean pressure field set up by the flow continuously drives the cross-flow fluid into the jet on the downstream side leading to enhanced entrainment relative to the upstream side and jet asymmetry. Autoignition of the jet depends sensitively on the cross-flow temperature. At the highest studied cross-flow temperature, spatially-isolated flame kernels form downstream of the jet, early on in the simulation. Although such flame kernels tend to propagate upstream, they get convected out of the domain. Later on, a strongly burning flame forms near the jet nozzle. At the lower cross-flow temperature, similar dynamics are observed significantly later in time and farther downstream from the nozzle.