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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.

Experimental visualization of current gasoline direct injection (GDi) systems are even more complicated especially due to the proximity of spray plumes and the interaction between them. Computational simulations may provide additional information to understand the complex phenomena taking place during the injection process. Nozzle flow simulations with a Volume-of-Fluid (VOF) approach can be used not only to analyze the flow inside the nozzle, but also the first 2-5 mm of the spray. A methodology to obtain plume direction and spray angle from the simulations is presented. Results are compared to experimental data available in the literature. It is shown that plume direction is well captured by the model, whilst the uncertainty of the spray angle measurements does not allow to clearly validate the developed methodology.

The Selective Catalytic Reduction (SCR) system has great potential in reducing NOx emissions. The urea-water solution (UWS) is the preferred method on vehicles for obtaining the ammonia, the required reductant for SCR. The UWS spray is necessary to transform exhaust gas into nitrogen and water and plays an important role in the performance of this system. The UWS needs to be properly mixed with the exhaust gas coming from the engine before entering the SCR, therefore the solution must be injected in the exhaust pipe in a way that it completely vaporizes in order to reduce deposit formation and guaranteeing a proper functioning and durability of the NOx reduction system. Achieving complete vaporization of the UWS spray is not an easy task, mainly due to reduced package space. Another challenge for converting UWS to ammonia is the latent energy in the exhaust.

A prototype multi-hole diesel injector operating with n-heptane fuel from a high-pressure common rail system is used in a high-pressure and high-temperature test rig capable of reaching 1100 Kelvin and 150 bar under different oxygen concentrations. A novel optical set-up capable of visualizing the soot cloud evolution in the fuel jet from 30 to 85 millimeters from the nozzle exit with the high-speed color diffused back illumination technique is used as a result of the insertion of a high-pressure window in the injector holder opposite to the frontal window of the vessel. The experiments performed in this work used one wavelength provide information about physical of the soot properties, experimental results variating the operational conditions show the reduction of soot formation with an increase in injection pressure, a reduction in ambient temperature, a reduction in oxygen concentration or a reduction in ambient density.

Actual combustion strategies in internal combustion engines rely on fast and accurate injection systems to be successful. One of the injector designs that has shown good performance over the past years is the direct-acting piezoelectric. This system allows precise control of the injector needle position and hence the injected mass flow rate. Therefore, understanding how nozzle flow characteristics change as function of needle dynamics helps to choose the best lift law in terms of delivered fuel for a determined combustion strategy. Computational fluid dynamics is a useful tool for this task. In this work, nozzle flow of a prototype direct-acting piezoelectric has been simulated by using CONVERGE. Unsteady Reynolds-Averaged Navier-Stokes approach is used to take into account the turbulence. Results are compared with experiments in terms of mass flow rate. The nozzle geometry and needle lift profiles were obtained by means of X-rays in previous works.

Proper initial conditions are essential to successfully perform a simulation, especially for highly transient problems such as Diesel spray injection. Until now, no much attention has been paid to the internal nozzle flow initialization because spray simulations are usually decoupled from the nozzle. However, new homogeneous models like Eulerian Spray Atomization (ESA) model allow to simulate the internal nozzle flow and the spray seamlessly. Therefore, the behavior of the spray for the first microseconds is highly influenced by the initial conditions inside the nozzle. Furthermore, last experiments confirm the presence of gas inside the nozzle between successive injections. This work deals with the initialization procedure in a way that mass flow rate and spray penetration curves are well predicted by the model.

The Fick's law is commonly used to model diffusion problems, but from some time ago it has been also used to model liquid jet atomization and mixing into gaseous atmosphere under certain hypothesis. An OpenFOAM computer model based on this principle has been developed and validated on axisymmetric geometries. This model has also been used to study the atomization process on the Engine Combustion Network (ECN) single-hole Spray A injector. Results have been compared to X-Ray and Mie-Scattering experimental data, showing that the Fick's law and its variants predict well the liquid core but tend to over-predict the spray angle/width in the first millimeters after the nozzle exit.

Transients in the rate of injection (ROI) with respect to time are ever-present in direct-injection engines, even with common-rail fueling. The shape of the injection ramp-up and ramp-down affects spray penetration and mixing, particularly with multiple-injection schedules currently in practice. Ultimately, the accuracy of CFD model predictions used to optimize the combustion process depends upon the accuracy of the ROI utilized as fuel input boundary conditions. But experimental difficulties in the measurement of ROI, as well as real-world affects that change the ROI from the bench to the engine, add uncertainty that may be mistaken for weaknesses in spray modeling instead of errors in boundary conditions. In this work we use detailed, time-resolved measurements of penetration at the Spray A conditions of the Engine Combustion Network to rigorously guide the necessary ROI shape required to match penetration in jet models that allow variable rate of injection.

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.

A study was conducted to investigate the evolution of liquid phase penetration of evaporating sprays under engine-like conditions, with diesel and biodiesel fuel blends. This study has been performed in a facility based on a single cylinder two-stroke direct injection Diesel engine operating at low rotational speed which provides a quiescent thermodynamic environment around TDC, when fuel is injected, realistic for current D.I. Diesel engines. Due to the absence of inlet or exhaust valves, very easy optical access to the combustion chamber can be provided through the cylinder head. Pure nitrogen is supplied to the engine as intake gas, in order to avoid combustion. The injection event is carried out by an electronically controlled common rail system. The injector is equipped with real 8-hole nozzles, with a hole diameter of 0.115 mm. Injection pressures in this study ranged between 30 and 160 MPa and different in-cylinder peak pressure and temperature values were considered.

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 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.

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.