Temporally gated imaging for investigation of atomizing sprays
Doktorsavhandling, 2016

Fuel sprays play an important role in the combustion process of modern compression ignition engines, but their dynamics are not well understood. This thesis focuses on time-gated imaging techniques as a means to study the optically dense spray formation region of these atomizing sprays. Initially, the performance of two ballistic imaging setups previously used in spray investigations was investigated. The investigation showed that the simpler of the two setups (2f) was less affected by changes in the time-gate setup, and was more robust to component misalignment. The 2f setup is therefore often preferable for time-gated spray investigations. Then, the ballistic imaging system was further developed with the use of three synchronized regenerative laser amplifiers. This system allowed three time-gated images with user defined inter-frame spacing to be generated. Based on these three images, two-dimensional acceleration data of larger liquid structures in the spray formation region were obtained. Such acceleration data can be used in the development of predictive computational spray codes. Next, ballistic imaging was used to study fuel sprays at elevated pressures and temperatures. This was the first time ballistic imaging was applied to sprays at engine-relevant conditions. The ambient conditions were varied and changes in the liquid/gas interfaces in the spray formation region were studied. It was shown that especially for single-component fuels the liquid-gas interfaces exhibited a significant change, which mostly correlated with the thermodynamic properties of the fuel. These findings contribute to the ongoing discussion regarding the potential transient supercriticality of fuel sprays in modern direct injection combustion engines. The investigation of the fuel sprays further showed that there is a need for a technique that provides depth-resolved data from the spray formation region. To this end, we developed a new approach termed time-gated sectioning. This setup captures backscattered light from the spray formation region, and was successfully able to generate a depth-resolution of around 0.3 mm. Collectively, the work presented in this thesis advances the use of time-gated imaging methods for spray investigations.

Ballistic imaging

Imaging through turbid media

Sprays

Velocimetry

Time-gated sectioning.

Optical Kerr effect

Ultrafast lasers

HA3, Hörsalsvägen 4, 41296 Göteborg
Opponent: Professor Claude Rozé, ESITech, University of Rouen, France

Författare

Mattias Rahm

Chalmers, Tillämpad mekanik, Förbränning

Evidence for supercritical mixing layers in the ECN Spray A

Proceedings of the Combustion Institute,; Vol. 35(2015)p. 1579-1586

Artikel i vetenskaplig tidskrift

Optical sectioning for measurements in transient sprays

Optics Express,; Vol. 24(2016)p. 4610-4621

Artikel i vetenskaplig tidskrift

Evaluation of optical arrangements for ballistic imaging in sprays

Optics Express,; Vol. 23(2015)p. 22444-22462

Artikel i vetenskaplig tidskrift

Visualization of acceleration in multiphase fluid interactions

Optics Letters,; Vol. 41(2016)p. 1404-1407

Artikel i vetenskaplig tidskrift

Gas/Fuel Jet Interfaces Under High Pressures and Temperatures

Fuel,; Vol. 168(2016)p. 14-21

Artikel i vetenskaplig tidskrift

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Ämneskategorier

Energiteknik

Annan fysik

ISBN

978-91-7597-332-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4013

HA3, Hörsalsvägen 4, 41296 Göteborg

Opponent: Professor Claude Rozé, ESITech, University of Rouen, France