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In order to comply with the increasingly restrictive limits of emissions and fuel consumption, researches are focusing on improving the efficiency of combustion engines. In this area, the aging of the injector and its effect on the injection development is not entirely analyzed. In this work, the rate of injection of a diesel injector at different stages of its lifetime is analyzed. To this end, a multi-hole piezoelectric injector was employed, comparing the injection rate measured at the beginning of its lifetime to the rate provided by the injector after aging, maintaining the same boundary conditions in both measurements. Injection pressures up to 200 MPa were used throughout the experiments. The results showed that the steady-state rate of injection was lower after the injector aged. Furthermore, the injector took a longer time to close the needle and end the injection, in comparison with the measurements done at earlier stages of its lifetime.

Most studies about common-rail diesel injection consider the fuel flow along the injector as isothermal. This hypothesis is arguable given the small diameter of the orifices along which the fuel flows, together with the expansions that take place across them. These phenomena may provoke variations in the fuel temperature, which in turn modify the fuel properties (i.e. viscosity, density, speed of sound…), thus influencing injector dynamics as well as the fuel atomization and mixing processes. The present investigation accounts for these effects by means of a 1D model for the fuel flow along a common-rail ballistic injector. Local variations of fuel temperature and pressure are considered by the model thanks to the implementation of the adiabatic flow hypothesis.

The influence of pressure and temperature on some of the important thermodynamic properties of diesel fuels has been assessed for a set of fuels. The study focuses on the experimental determination of the speed of sound, density and compressibility (via the bulk modulus) of these fuels by means of a method that is thoroughly described in this paper. The setup makes use of a common-rail injection system in order to transmit a pressure wave through a high-pressure line and measure the time it takes for the wave to travel a given distance. Measurements have been performed in a wide range of pressures (from atmospheric pressure up to 200 MPa) and temperatures (from 303 to 353 K), in order to generate a fuel properties database for modelers on the field of injection systems for diesel engines to incorporate to their simulations.

A computational one-dimensional model of a solenoid operated common-rail ballistic injector has been performed and implemented in the AMESim software. A complete characterization of the different elements that comprise the system has been carried out in order to describe its behaviour. The model has been validated against mass flow rate experimental data along a wide range of engine-like operating conditions by varying the injection pressure, energizing time and injection temperature. The setup of the experimental facility is also described in the paper, with special attention to the injection temperature control. Results made it possible to quantify the influence of this injection temperature on the dynamic behaviour of such kind of injectors, where the needle lift is not limited and thus the viscous friction is deemed to be important on both the opening and closure stages of the injection event.

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.

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).

The aim of this paper is to present an experimental study of the influence of using biodiesel blended fuels on a standard injection system taken from a DI commercial Diesel engine. The effects have been evaluated through injection rate measurements, spray momentum and spray visualization at ambient temperature (non-evaporating condition). These tests have been done using five different injection pressures, from 300 to 1600 bar, and three back pressures: 20, 50 and 80 bar. It is well known that fuel properties like density or kinematic viscosity are higher in vegetable oils and strongly affect how injection system operates. The tests showed that the use of biodiesel fuels leads to a higher mass flow when the injector is fully open. The spray pattern is also affected, biodiesel penetrates more and the spray is narrower. Some explanations are provided in this paper in order to understand better the injection process when vegetable oils are used.

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.

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 aim of this paper is to identify and quantify the influence of injection parameters and running conditions on the air/fuel mixing and diffusion combustion process in a D.I. Diesel engine. With this work, it is intended to improve the understanding of some of the processes that take place in the combustion chamber of D.I. Diesel engines. An analysis of the relationship between the injection rate and the rate of heat release through the physical variables that directly participate in the injection-combustion process is performed. To approach the problem, a parameter called “Apparent Combustion Time (ACT)” is defined. A theoretical analysis that allows the identification and quantification of the main physical variables that directly affect the air/fuel mixing process has been performed. This theoretical approach enabled to find out the relationship between the ACT and the injection and in-cylinder conditions in the diffusion combustion phase.