Experimental measurements of cavitating flows inside fuel injection equipment

In the fuel injection equipment of internal combustion engines, the complexity of two-phase flows arising within the injectors represents a critical aspect in the intricate realm of engine design. This highly complex phenomenon involves the simultaneous presence of liquid fuel and vaporised fuel within the injector, adding layers of sophistication to the fuel atomization and the lifetime of the injector. Hence, understanding the two-phase flow is paramount for achieving efficient combustion, emission control, overall engine performance, and the ongoing evolution of internal combustion engines. The investigation of vapour content within injectors is a complex task that relies on a combination of computational fluid dynamics (CFD) and experimental studies. CFD simulations provide a virtual platform to model and analyse the intricate fluid dynamics, thermodynamics, and phase changes occurring within the injector, and offers insights into the morphology, dynamics, and vaporisation of the fuel, allowing for a detailed examination of the two-phase flow phenomena. However, the validation of CFD models requires experimental studies to ensure accuracy and reliability. Experimental measurements offer a real-world validation of the simulated results, helping to bridge the gap between theoretical predictions and practical observations. This work is dedicated to three major cutting-edge experimental techniques in elucidating the behaviour of the two-phase flow inside the injector as well as near nozzle spray characteristics; Initially, as research on renewable and alternative fuels is crucial for improving the energy and environmental efficiency of modern gasoline internal combustion engines, high-speed imaging using Diffuse Backlight Illumination (DBI) was employed to investigate the transient two-phase flow field arising in the internal geometry and the near-nozzle spray region of gasoline injectors. Experiments were conducted at realistic operating conditions comprising an injection pressure of 100 bar and ambient pressures in the range of 0.1 – 6.0 bar to cover the entire range of chamber pressures prevailing in Gasoline Direct Injection engines. Moreover, high-flux synchrotron radiation was employed in a time-resolved manner to characterise the distinct topology features and dynamics of different cavitation regimes arising in a throttle orifice with an abrupt flow-entry contraction. Radiographs obtained through both X-ray phase-contrast and absorption imaging have been captured at 67890 frames per second. X-ray phase-contrast imaging offers sharp refractive index gradients in the interface region for capturing fine morphological fluctuations of transient cavitation structures, whereas absorption imaging is explicitly correlated with the projected vapour thickness in a line-of-sight manner. Finally, the capability of cold neutron imaging to quantify cavitation, in terms of vapour content, within an orifice of an abruptly constricting geometry is demonstrated. Despite the time-averaged nature of this technique, the morphology of transient vaporous structures is clearly visualised due to the high spatial resolution achieved, revealing subtle differences between fluids of different rheological properties. As a result, the potential of incorporating neutron irradiation for the quantification of two-phase flows in metallic microfluidics devices is established.