Passive scalar interface in a spatially evolving mixing layer (A. Attili and D. Denker)

Quartz nozzle sampling (D. Felsmann)

Dissipation element analysis of a planar diffusion flame (D. Denker)

Turbulent/non-turbulent interface in a temporally evolving jet (D. Denker)

Dissipation elements crossing a flame front (D. Denker and B. Hentschel)

Particle laden flow (E. Varea)

Turbulent flame surface in non-premixed methane jet flame (D. Denker)

DNS of primary break up (M. Bode)

Diffusion flame in a slot Bunsen burner (S. Kruse)

Various quantities in spatially evolving jet diffusion flame (D. Denker)

High repetition chamber to determine laminar flame speeds

Laminar flame speed is one of the most important fundamental properties of a combustible mixture, regarding its reactivity, diffusivity, and exothermicity. It is defined as the propagation speed relative to the unburned mixture of a steady, laminar, one-dimensional, planar, stretch-free, and adiabatic flame. The accurate knowledge of laminar flame speed is essential for validating kinetic mechanisms. Also, it can serve as a key scaling parameter in turbulent combustion. Here, spherically expanding flames are investigated, requiring a data reduction scheme, where flame speeds are extracted from flames extrapolated to a virtual, unstretched flame front at an infinite flame radius.

Description of the setup

The facility at ITV consists of a spherical combustion chamber with an inner diameter of 100 mm. The chamber is designed to withstand high combustion pressures up to 240 bar at elevated temperatures. Propagating flames can be optically accessed via two quartz windows with a diameter of 50 mm positioned on opposite sides. The location of the spherically propagating flame is imaged using a dual-field-lens Schlieren arrangement. It is combined with a high-speed CMOS camera (LaVision HighSpeedStar 6). Images are taken at 25,000 frames per second (fps) and with a resolution of more than 10 pixel/mm. A pulsed high-power LED is used as a light source emitting light in a range of 530-535 nm.

An external mixing vessel, directly connected to the combustion chamber via pipes, is employed for an external preparation of the fuel/oxidizer mixture. Careful and accurate preparation of the fuel/air mixture is essential in laminar flame speed experiments. The amount of fuel needed is calculated as a function of equivalence ratio, temperature, and pressure. The partial pressure method is used to measure and control the filling process accurately. Before sparking, the mixture is allowed to settle. A high voltage coil and capacitor discharge is used to ignite the mixture via elongated spark plug electrodes at the midpoint of the vessel. Post-processing of the propagating flames, recorded under quasi-isobaric conditions, yields information of the expanding flame radius over time, which can be related to the flame speed.

Experimental uncertainties are adequately assessed, including mixture, temperature, pressure, image acquisition, and extrapolation uncertainties, to ensure the high quality of the validation data sets for chemical kinetic modeling, e.g., of renewable bio-hybrid fuels. The laminar burning velocity is also a suitable metric to assess the flammability of a premixed fuel/oxidizer mixture as of mildly flammable low-global warming potential refrigerants. Refrigerant flames are associated with extremely low flame speeds, making their determination extremely challenging.