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Droplet-Wall and Spray-Wall Interaction at Increased Ambient Pressure and Wall Temperature
von Jochen StratmannIn direct-injection gasoline engines, the interaction of the fuel spray with a wall of the combustion chamber may influence the mixture formation process and, as a consequence, the engine efficiency and emissions. Detailed knowledge of the fundamental phenomena occurring throughout this process is therefore a prerequisite for the development of such engines.
Spray-wall interaction models employed in numerical tools for engine development are based on a limited number of experimental investigations, of which many are conducted with respect to applications other than fuel injection. This work aims at contributing to the clarification of the role of the wall temperature and the ambient gas pressure on the droplet-wall and spray-wall interaction process at gasoline engine-relevant conditions.
The results of this study feature a classification of droplet-wall interaction regimes in dependence on the initial droplet Weber-number, the wall temperature as well as the ambient pressure. The properties of the secondary droplets resulting from droplet breakup are characterized as to their size, number, velocity, trajectory and diameter-velocity correlation using Phase-Doppler Anemometry. The secondary droplet diameter distribution is approximated by a suitable distribution function. The parameters of this function are formulated in terms of the influencing properties, leading to a statistical droplet-wall model.
In addition, near-wall spray details, i. e. temporally and spatially resolved droplet size and velocity components, of an engine-like spray are determined at increased gas density and variable wall temperature. The results, which reveal the transient character of the wall spray, are suitable to develop an understanding of the process and may serve as a basis for the comparison with numerical simulations.
It is acknowledged that parts of this study are a contribution to the EUproject ”Droplet Wall Interaction Phenomena of Relevance To Direct Injection Gasoline Engines” (DWDIE) financed by the EU within the 5 th framework program under contract number ENK6-CT2000-00061.
Spray-wall interaction models employed in numerical tools for engine development are based on a limited number of experimental investigations, of which many are conducted with respect to applications other than fuel injection. This work aims at contributing to the clarification of the role of the wall temperature and the ambient gas pressure on the droplet-wall and spray-wall interaction process at gasoline engine-relevant conditions.
The results of this study feature a classification of droplet-wall interaction regimes in dependence on the initial droplet Weber-number, the wall temperature as well as the ambient pressure. The properties of the secondary droplets resulting from droplet breakup are characterized as to their size, number, velocity, trajectory and diameter-velocity correlation using Phase-Doppler Anemometry. The secondary droplet diameter distribution is approximated by a suitable distribution function. The parameters of this function are formulated in terms of the influencing properties, leading to a statistical droplet-wall model.
In addition, near-wall spray details, i. e. temporally and spatially resolved droplet size and velocity components, of an engine-like spray are determined at increased gas density and variable wall temperature. The results, which reveal the transient character of the wall spray, are suitable to develop an understanding of the process and may serve as a basis for the comparison with numerical simulations.
It is acknowledged that parts of this study are a contribution to the EUproject ”Droplet Wall Interaction Phenomena of Relevance To Direct Injection Gasoline Engines” (DWDIE) financed by the EU within the 5 th framework program under contract number ENK6-CT2000-00061.