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Dynamics of Transient Fuel Injection, Mixing, and Auto-Ignition

The transient behavior of auto-ignition under turbulent fuel injection is of great importance for several engineering applications, including diesel and HCCI engines and scramjets. Understanding auto-ignition also is required for situations where such events are undesired (e.g. gas turbines, SI engines) and could lead to a catastrophic failure. Autoignition in turbulent environments is a complex phenomenon, where the chemical time scales responsible for ignition are on the same order as the fluid mechanic time scales and thus both chemical kinetics and turbulence play a major role in the events that lead to ignition and flame stabilization.

We are currently investigating auto-ignition using advanced optical and laser-based diagnostics in canonical configurations to isolate the relative roles of flow turbulence, turbulent mixing, and reaction chemistry on auto-ignition processes of turbulent fuel jets injected into a high-temperature, vitiated oxidizer stream.

Below we show a schematic of the OSU auto-ignition burner (AIB) and video of the transient operation. Each "burst" is less than 50 ms and we collect more than 1000 individual sequences at each operating condition.

 

(Top): Photograph of Auto-Ignition Burner (Bottom): Imaging setup for multi-view high-speed imaging

Auto-ignition Experiment in Motion 

We have examined the role of mixing rate fluctuations on auto-igntion. Below is a sample image sequence of time-resolved mixture fraction, temperature, and OH* (representing the onset of combustion) in a Re = 40,000 DME fuel jet issuing into a T = 1330 K coflow. Each image sequence corresponds to approximately 5 ms of real time.

Results show that for the current fuels and thermodynamic conditions, auto-igntion occurs in very lean regions with low values of scalar dissipation rate [1, 2]

10-kHz image sequences of (Top) mixture fraction (Middle) OH* representing the onset of ignition and flame stabilization (Bottom) temperature in a Re = 40,000 DME fuel jet issuing into a T = 1320 K vitiated coflow

 

References

[1] Papageorge, M., Arndt, C.M., Fuest, F., Meier, W., Sutton, J.A., “High-Speed Mixture Fraction and Temperature Imaging of Pulsed, Turbulent Fuel Jets Auto-Igniting in Vitiated Co-Flows,” Experiments in Fluids, 2014, 55(7), 1763.

[2] Arndt, C.M., Papageorge, M., Fuest, F., Sutton, J.A., Meier, W., Aigner, W., "The Role of Temperature, Mixture Fraction, and Scalar Dissipation Rate on Transient Methane Injection and Auto-Ignition in a Jet-in-Hot-Coflow Burner", Combustion and Flame, 2016, 167, 60-71.

[3] Saksena R., Sutton, J.A., "Transient and Steady-State Behavior of Auto-Igniting Propane and Dimethyl Ether Fuel Jets in High-Temperature Vitiated Coflows", accepted, Proceedings of the Combustion Institute

[4] Arndt, C.M, Papageorge, M., Fuest, F., Sutton, J.A., Meier, W., "Experimental Investigation of the Auto-Ignition of a Transient Propane Jet-In-Hot-Coflow", accepted, Proceedings of the Combustion Institute