ElsevierBenajes Calvo, JV.; Payri Marín, R.; Bardi, M.; Marti-Aldaravi, P. (2013)

Inside a DISI engine, a wide range of pressure and temperature conditions are possible, and with the current evolution of the systems, many of the conditions are subject to be encountered at the moment of injection. Given the great differences between Diesel injectors and GDi fuel injectors, the effects of such conditions on the development of the fuel injected can cause phenomena like flash boiling and spray collapse that fundamentally change the behavior of sprays. In this work, the Spray G injector developed by Delphi for the Engine Combustion Network (ECN) group has been tested in a High Pressure High Temperature Constant Pressure Flow Rig (HPHT-CPFR) in a wide range of experimental conditions capturing the liquid and vapor phases of the spray by means of DBI and Schlieren imaging. The work presents the results obtained by spray visualization through comparisons of parametric variations with special focus on the collapse of the spray that occurs under high ambient temperature and density conditions. Spray collapse has been described by showing the direct increase that can cause in spray penetration and the great closing effect that can produce to the aperture of the spray (spray angle). Several contour comparisons using the raw images and the detected contours have been discussed in order to support and further explain the observed trends.

A combined experimental and computational investigation has been performed in order to evaluate the influence of physical properties of biodiesel on the injection process in a common-direct injection system with second generation solenoid injectors. For that purpose, after a complete characterization of the system, which involved mechanical and hydraulic characterization, a one-dimensional model has been obtained and extensively validated. Simulations have then been performed with a standard Diesel and a 100% rape methyl ester (RME) biodiesel which allowed a comparison and analysis of the dynamic response of the injector to be done. Different injection strategies involving main injection and main plus post-injection have been used to explore the impact of the use of biodiesel on the performance and stability of solenoid injectors.As far as the dynamic response of the injector is concerned, the results obtained have clearly shown that the use of biodiesel affects the dynamic response of the needle, especially at low injection pressures. The behavior of the system under multi-injection strategies (main plus post injection) has been also evaluated determining for different operating conditions (injection pressures and backpressures) the minimum dwell time between injections to assure a stable behavior in the injection process (mass flow rate).Important differences have been found between biodiesel and standard diesel in this critical parameter at low injection pressures, becoming less important at high injection pressure. Finally, a modification on the injector hardware has been proposed in order to compensate these differences.

a b s t r a c tIn this research, two Engine Combustion Network (ECN) mono-orifice nozzles, referred to as Spray C and Spray D respectively, were analyzed by performing visualization tests through Schlieren and Diffused Backlight Illumination (DBI) techniques under a wide range of ambient conditions in a non-reactive atmosphere. Spray C presents a straight nozzle designed with a sharp fillet in opposition to Spray D that has similar hydraulic properties, but with a convergent nozzle construction and a smoother corner. The experiments were carried out injecting two distinct fuels at different injection pressure ranges, from 50 MPa to 150 MPa with n-dodecane and to 200 MPa for diesel. The images were processed with Matlab home-built routines to calculate parameters as spray penetration, spreading angle, quasisteady liquid length, as well as the spray penetration derivative respect to the square root of time, presented in this document as R-parameter. The results showed a clear influence of nozzle geometry in all measured parameters, due mainly to the nature of Spray C to cavitation, which increase the spreading angle and consequently a reduction in vapor penetration. On the other hand, fuel properties also affected spray penetration due to its dependency on viscous forces expressed in terms of the Reynolds number and its volatility in case of liquid length. This last parameter was calculated employing two processing methodologies, finding a good general agreement between them.

Simulating liquid spray first and second atomization is not an easy task. Many models have been developed over the past years, but Eulerian ones have proved their better performance for the dense zone of the spray. In this work a new compressible Eulerian model is used to compute the internal flow together with the spray. Up to five two-equation turbulence models have been tested and its influence is remarkable in terms of spray behavior, but also greatly affects the mass flow rate and the momentum flux. At the end, SST k − ω model proves to be best than the others. Additionally, different types of inlet boundary conditions have been also tested and analyzed. Results when compared with previously obtained experimental data show that the commonly used for external flow time-varying velocity boundary condition gives also good performance for the internal flow.