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In this paper, a special technique for visualizing the first 1.5 millimetres of the spray has been applied to examine the link between cavitation phenomenon inside the nozzle and spray behaviour in the near nozzle field. For this purpose, a real Diesel axi-symmetric nozzle has been analyzed. Firstly, the nozzle has been geometrically and hydraulically characterized. Mass flow measurements at stationary conditions have allowed the detection of the pressure conditions for mass flow choking, usually related with cavitation inception in the literature. Nevertheless, with the objective to get a deeper knowledge of cavitation phenomenon, near nozzle field visualization technique has been used to detect cavitation bubbles injected in a pressurized chamber filled with Diesel fuel. Using backlight illumination, the differences in terms of density and refractive index allowed the distinction between vapour and liquid fuel phases.

It is known that one of the main parameters that govern the spray penetration development is spray momentum flux. In this paper, a model capable to predict the development of the spray penetration using as an input the temporal variation of the spray momentum flux is presented. The model is based on the division of the momentum flux signal in momentum packets sequentially injected and the tracking of them inside and at the tip of the spray. These packets follow a theoretical equation which relates the penetration with the ambient density, momentum and time. In order to validate the method, measures of momentum flux (impingement force) and macroscopic spray visualization in high density conditions have been performed on several mono-orifice nozzles. High agreement has been obtained between spray penetration prediction from momentum flux measurements and real spray penetration from macroscopic visualization.

This paper deals with the problem of quantifying and predicting the macroscopic spray behaviour as a function of the parameters governing the injection process. The parameters studied were ambient gas density as a representative parameter external to the system, and nozzle hole diameter and injection pressure as influential system parameters. The main purpose of this research is to validate and extend the different correlations available in the literature to the actual Diesel engine conditions, i.e. high injection pressure, small nozzle holes, severe cavitating conditions, etc. The sprays from five axi-symmetrical nozzles with different diameters are characterized in two different test rigs that can reproduce the real engine in-cylinder air density and pressure. The wide parametric study that was performed has permitted to quantify the effects of the injection pressure, nozzle hole diameter and environment gas density on the spray tip penetration.

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.

The characteristic parameters and the evolution of continuous Diesel sprays injected against a high density gas have been investigated using high speed photography and phase Doppler anemometry. The injector used for these tests was a two-spring one providing different injection conditions. Three test sections were analyzed at 10, 20 and 30 mm from the injector with several radial measurements for each one. The obtained results provided qualitative and quantitative information about the macroscopic evolution of the spray, but also about the drop velocity distribution and drop size evolution.

The paper describes the theoretical and experimental development of the intake manifold for a 12-liter, 6-cylinder supercharged Diesel engine with intercooling. The objective has been to obtain a torque diagram optimum for traction, i.e. with the maximum torque at a low engine rpm without penalizing the peak power, in addition the design has to keep a reduced fuel consumption and low smoke level. To meet these requirements, the solution adopted has been to obtain the cylinder filling by means of the combined effect of the turbocharger and the geometry of the intake manifold. The design of the manifold is based on the use of lengths and diameters for the pipes appropriate to obtain the desired volumetric efficiency diagrams, avoiding the use of intermediate reservoires. This solution has some advantages for the case of big automotive engines with intercooling, since usually long pipe lengths among turbocharger, intercooler and cylinders are needed.

To approach the problem of the design of more correct geometries for exhaust pipes, two consecutive analysis are necessary. In the first part of this report it is intended to establish the relationship among the pressure-alpha plots of a point of the exhaust duct near the exhaust port and the fundamental parameters which characterize the scavenging process. In that way, the most suitable pressure-alpha plot for each specific use can be determined via experimental work. In the second part of the report, a calculation model is presented. The model based on the method of characteristics, allows to compute analytically the plots of pressure at the exhaust port versus crankangle for a given exhaust duct configuration. With this calculation model different outlines can be performed analytically and choose the one that complies with the required coefficients of the scavenging process for several engine rpm.

It exists the possibility of adopting variable valve timings to reduce pump-losses in spark-ignition engines. With this method, engine load regulation can be achieved mainly by acting over the total time that the inlet valve remains open, and eliminating the throttle valve in an ideal case. The timing diagram (total opening valve and angular phase) should depend on the engine speed and load desired in each moment. The mechanical system for the proposed regulation system is a four-bar mechanism which is now in a stage of final adjustment for a monocylinder engine. In order to get the valve timing, a calculation model for the inlet and exhaust processes has been developed and is presented in this article, as well as the results obtained.