The present work comparably examines four different twin-fluid atomizers operated under the same operating conditions. Spray formation was examined by several approaches. The internal flow pattern was estimated using a simplified analytical approach, and the results were supported by the observation of the liquid discharge in the near-nozzle region. A high-speed back illumination was used for visualisation of the primary breakup. In the region of fully developed spray, the dynamics of droplets was studied using a phase-Doppler analyser (PDA). The information obtained from all methods was then correlated. Results show that the spray formation process depends mainly on the internal design of twin-fluid atomizer at low gas to liquid ratios (GLR). The amount of gas influences the character of the internal two-phase flow, a mechanism of the liquid breakup, droplet dynamics and a resulting drop size distribution. Differences among the atomizers are reduced with the increase in GLR. Moreover, it was shown that a certain mixing process can inherently create the annular internal flow which generates a stable spray characterized by relatively low mean droplet size.

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The method for direct injection of fuel in the cylinder of an IC engines is important to high-efficiency and low-emission performance. Optical spray diagnostics plays an important role in understanding plume movement and interaction for multihole injectors, and providing baseline understanding used for computational optimization of fuel delivery. Traditional planar or line-of-sight diagnostics fail to capture the liquid distribution because of optical thickness concerns. This work proposes a high-speed (67 kHz) extinction imaging technique at various injector rotations coupled to computed tomography (CT) for time-resolved reconstruction of liquid volume fraction in three dimensions. The number of views selected and processing were based on synthetic (modeled) liquid volume fraction data where extinction and CT adequately reconstructed each plume. The exercise showed that for an 8-hole, symmetric-design injector (ECN Spray G), only three different views are enough to reproduce the direction of each plume, and particularly the mean plume direction. Therefore, the number of views was minimized for experiments to save expense. Measurements applying this limited-view technique confirm plume-plume variations also detected with mechanical patternation, while providing better spatial and temporal resolution than achieved previously. Uncertainties due to the limited view within pressurized spray chambers, the droplet size, and optically thick regions are discussed.

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This work experimentally examines the primary atomization processes in a newly developed atomizer, similar to effervescent atomizer concept, at low pressures and low gas-to-liquid ratios (GLR). Several experimental and post-processing techniques are applied to investigate the spray spatial evolution. The near-nozzle area is captured by a high-speed camera with a long-distance microscope. Further, characteristics of the developed spray are investigated by a phase-Doppler analyser (PDA). The high-speed recordings are processed by the proper orthogonal decomposition (POD). The frequency analysis of examined phenomenon is done by the fast Fourier transformation (FFT) at selected positions in the images. The POD enables to sort out data according to the importance of characteristic shapes occurring in the recordings. The velocity and dimensions of discharging liquid are measured in images by a point-tracking method. Dimensionless criteria are estimated to describe the atomization principles where several new findings are found comparing the previous studies. The spatial spray evolution is described by the processed PDA data. A simplification, based on the Stokes number, is used to estimate a gas motion in the spray. This approach enables to investigate the interaction between the spray and ambient atmosphere. The combination of experimental and post-processing techniques confirms the previous findings of the improved effervescent atomizer. In other words, the atomizer operates inherently at annular twophase flow regime which, however, leads to a specific atomizing mechanism i.e. bubble bursts, the same as in the effervescent spraying process. However, an importance of the interaction between the two following bubble bursts is highlighted as driving atomization mechanism. This specific behaviour is reason why the atomizer can be operated at low consumption of gas and low-pressure regimes. Moreover, the applied experimental and post-processing techniques indicate a potential for further advanced data post-processing of the stochastic processes of liquid atomization.

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Mie scattering, Schlieren technique and Raman spectroscopy are used to analyse air entrainment and mixture distribution in sprays at Diesel engine-relevant ambient conditions. Mixture formation for Diesel, gas-to-liquid Diesel, biodiesel (rapeseed methyl ester) and ethanol is investigated. The utilization of different fuels leads to locally equal mass flow ratios of fuel and ambient gas in the spray. The air entrainment process is dominated by conservation of the total spray momentum flux. Shortly after nozzle exit, the amount of ambient gas in the spray is high enough to make it the dominating component of the flow. Already 7 mm after the nozzle exit, the mass flow of ambient gas equals the mass flow of fuel. Also, the local mixture distribution in the spray-investigated by means of Raman spectroscopy-is fuel independent. Different physical properties of the fuels do (nearly) not influence the air entrainment and macroscopic mixture formation process, as the differences and the amount of fuel are too small to have a significant effect. Injection pressure and the resulting momentum flux are the dominating parameters of mixture formation. Because of the magnitude of the ambient gas content, the spray can be regarded as a gas jet.

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