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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.

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.

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.

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.

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.

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.

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).