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The objective of the paper is the characterization of the macroscopic behavior of Diesel sprays by focusing in at the first instants of the injection process at which the spray is clearly affected by the injector needle dynamic. There are several works dealing with the characterization of Diesel sprays in stationary conditions. Most of them conclude with empirical correlations which predict spray tip penetration as a function of the most important parameters involved in the injection process, such as: injection pressure, gas ambient density, hole diameter and time elapsed from the start of injection. In all these experiments, authors find similar power law dependencies with more or less high level of confidence. Nevertheless, few works have tried to validate or to obtain new correlations for the first instants of the injection process where the spray develops in not stationary conditions because of the influence of injector needle lift.

Starting and operating of diesel engines in cold conditions is a common and important problem. Many factors such as ambient conditions, fuel properties, fuel injection, cranking speed, etc, affect cold engine functionality. In order to improve diesel engine cold start, it is essential to understand better these problems. In this paper the injection development at cold temperatures is studied, since it is an important parameter that affects the fuel interaction with the air, so the future combustion process would also be influenced. In particular, a hydraulic characterization of diesel injection is made, using specialized test rigs that simulate real engine in-cylinder air pressure and density; the fuel is injected from three axi-symmetric convergent nozzles at several injection pressures (30, 50, 80, 120 and 180 MPa), two chamber densities and two temperatures of 255 K (winter) and 298 K (reference).

In Diesel injection Systems, cavitation often appears in the injection nozzle holes. This paper analyses how cavitation affects the Diesel spray behavior. For this purpose two spray parameters, mass flux and momentum flux, have been measured at different pressure. We know that cavitation brings about the mass flux choke, but there are few studies about how the cavitation affects the momentum and the outlet velocity. The key of this study is just the measurement of the spray momentum under cavitation conditions.

An experimental study has been performed to evaluate the impact of different needle partial lifts on the nozzle orifices flow. A prototype injector with a multi-orifice nozzle was used. This injector allows controlling the needle lift at different percentages of maximum lift. Different measures of mass flow rate and spray momentum flow at several rail pressures (up to 200 MPa) were made in order to observe the effect of different needle lift percentages on the amount of fuel injected and momentum of the jet. The influence of partial needle lifts on nozzle orifices flow was estimated by using non-dimensional parameters of discharge coefficient (Cd), velocity coefficient (Cv) and area coefficient (Ca). The results show an interesting reduction in nozzle discharge coefficient at partial lift. This reduction of Cd value at partial needle lift is not only due to the drop in the velocity coefficient but also to a reduction of the effective orifice area.