In modern society, sprays are ubiquitous; they are used for painting, cooling, misting, washing, applying chemicals, dispersing liquids, etc. In medicine, inhaled droplets must satisfy a range of size. In spray coating and painting the major challenge consists in the production of droplets which will deposit and dry into uniform layers of desired thickness. Numerous other examples related to many industrial domains could also highlight the importance of understanding the physic of spray generation.
Nevertheless, the most significant example of a spray application concerns the injection of liquid fuel into combustion engines. Internal combustion, used in cars, and gas turbines engines, used in planes, are two very important examples of devices which provide mechanical power using most often liquid fuel spray. Due to an increased desire for both efficiency improvement and reducing pollutant emission, the interest in the fuel-injection process has expanded during the last couple of decades. To burn liquid fuels efficiently, it is necessary to convert the liquid stream into a vapor stream and mix the vapor into surrounding air. Even though various alternative strategies have been suggested and tested, it is believed that combustion modes will continue to use liquid fuels especially for boat and air transportation. It is then of importance to understand liquid fuel injection using spray systems and the transition from liquid to gas in order to obtain more efficient combustion systems and reduce the emission of pollutants. This understanding is also important for the case of bio-liquid fuels such as Ethanol, Butanol, Tailor-made and Bio-diesel fuels.
Over the past two decades there has been a consequent efforts to provide both more detailed experimental data and more predictive simulation results. Despite this effort, the amount of spray information that is currently accessible remains largely limited by the lack of direct observation. In other words, the scattering nature of atomizing sprays is responsible for the blurring and hiding of any complex fluid mechanical processes. Thus, detailed information of the near-nozzle region is still missing. In addition multiple light scattering limits the possibility in measuring the droplets size within a dense cloud of droplets. As a result, the complete 3D field of droplets is rarely characterized and only local point measurements on the spray edges are provided. Finally, another quantity of importance which is almost never reported is the spray temperature from the liquid injection to the evaporation zone.
Visualizing in detail the spray dynamics in the near nozzle region, measuring both the droplets size and concentration in 3D with high spatial/temporal resolution, and determining the temperature gradients over the complete spray system, is the only possible way to fully depict a spray system. The Spray-Imaging project aims at addressing all these issues by developing and applying, three novel laser imaging techniques beyond the state of the art for the detailed characterization of various relevant spray systems. To optimize the development of those three techniques computational Monte Carlo simulation will also be initiated. The resulting unique experimental data will be well documented on an open source webpage where any modeler will have free access to them for the validation of their model.
The ultimate goal of the project is to discover and analyze unobserved fluid mechanics phenomena responsible for spray formation and to characterize in 3D the finally formed evaporating spray. The techniques needed to achieve this end do not exist today and are being developed and applied through this project. This work presents, then, a possible way to significantly increase the future knowledge of liquid-to-gas transition occurring in each atomizing spray system. It would certainly open doors for better prediction of spray behavior, ultimately leading to smarter injection devices and to the design of cleaner and more efficient liquid fuel-based combustion engines.
