Dipl.-Ing Benjamin Bork

Kontakt

Experimental investigation of droplet evaporation under extreme ambient conditions using laser diagnostic methods with high temporal resolution

Introduction and Motivation

The injection of liquid fuel into a supercritical environment holds the potential for improving processes related to energy conversion such as the consumption minimization in supercharged combustion engines or the control of combustion instabilities. The targeted use of supercritical injection in technical processes is inhibited by the incomplete understanding of the governing physics. This applies particularly to the break-up, the evaporation and the mixing of a fluid at the transition from subcritical to supercritical conditions. Detailed experimental studies help to overcome the shortage of valuable data which are essential for model development and validation.

The overall objective is the description of the time dependent progress of the droplet during its transition to the supercritical state as profoundly as possible by means of experiments. These experiments help to improve the understanding and modeling of the governing physics and build the foundation for the development of innovative fuel injection technologies in the future.

Method and Theory

Aiming for a comprehensive experimental study of the evaporation and mixing process of isolated droplets injected into a super- or near-critical environment the data will be used in cooperation with Illya Shevchuk to develop a modeling approach that applies to all regimes relevant in the process. This purpose requires well defined boundary conditions for the experiment. In contrast to sprays, the generation of single droplets allows for reproducible boundary conditions when injected into an optically accessible chamber containing an atmosphere of high pressure and temperature. The improvement and application of different measurement techniques is expected to provide quantitative and exact data on the droplet's morphology, its size, velocity, the concentration of the droplet substance in the mixing zone and the transition from sub- to supercritical state.

Proceeding

The most challenging aspects of this project are on the one hand the development of a system that allows for the controlled injection of single droplets in a gaseous atmosphere whose temperature and pressure can be varied up to the supercritical regime of the droplet substance. On the other hand there are only a few measurement techniques that hold the potential to investigate the transition to the supercritical state and the mixing process with the surrounding gas. In this project a number of different optical methods will be tested for adaptability to these demanding measurement tasks. The most promising methods will be used to measure the characteristics of the model system consisting of acetone droplets in an atmosphere of oxygen and nitrogen. The gas pressure and temperature will be increased up to the supercritical region of acetone (p_crit ~48±4bar, T_crit ~508±2K).

A callibration chamber is used to investigate the photophysics of well controlled mixtures of Nitrogen, Oxygen and Acetone. The insights gained from this test rig will enable the quantitative measurement of the composition of the vapor surrounding the evaporating drop and help to distinguish between vapor and liquid phase.

Publications

Oldenhof, E. ; Weckenmann, F. ; Lamanna, G. ; Weigand, B. ; Bork, B. ; Dreizler, A. :

Experimental investigation of isolated acetone droplets at ambient and near-critical conditions, injected in a nitrogen atmosphere.

In: Proceedings of the EUCASS 2011 - 4th European Conference for Aerospace Science, Saint Petersburg, Russland.

[Konferenz- oder Workshop-Beitrag] , (2011)

Weckenmann, F. ; Bork, B. ; Oldenhof, E. ; Lamanna, G. ; Weigand, B. ; Böhm, B. ; Dreizler, A. :

Single Acetone Droplets at Supercritical Pressure: Droplet Generation and Characterization of PLIFP.

In: Zeitschrift für Physikalische Chemie, 225 (11-12) pp. 1417-1431.

[Artikel] , (2011)

Heeger, C. ; Karimi, N. ; Bork, B. ; Dreizler, A. :

Investigations of flashback in a lean premixed swirl flame.

In: European Combustion Meeting, 2011, Cardiff.

[Konferenz- oder Workshop-Beitrag] , (2011)

Bork, Benjamin ; Böhm, B ; Heeger, Christof ; Chakravarthy, S. ; Dreizler, A. :

1D high-speed Rayleigh measurements in turbulent flames.

In: Appl. Phys. B

[Artikel] , (2010)