Raul Payri

Analysis of the influence of diesel nozzle geometry in the injection rate characteristic

An experimental research study was carried out to analyze the influence of different orifice geometries (conical and cylindrical) on the injection rate behavior of a Common-Rail fuel injection system. For that purpose, injection tests in two different injection test rigs were conducted. This behavior of the injection rate in the different nozzles was characterized by using the non-dimensional parameters of cavitation number (K), discharge coefficient (Cd) and Reynolds number (Re). First, some relevant physical properties of the injected fuel were accurately characterized (density, kinematic viscosity and sound speed in the fluid) in a specific test rig as a function of the operating conditions (pressure and temperature). The behavior of both nozzles was analyzed at maximum injector needle lift under steady flow conditions in a cavitation test rig. Injection pressure and pressure at the nozzle discharge were controlled in order to modify the flow conditions. In addition, the nozzles were characterized in real unsteady flow conditions in an injection-rate test rig. From the raw results, the values of the relevant parameters were computed, and the occurrence of cavitation was clearly identified

Measurements of Spray Momentum for the Study of Cavitation in Diesel Injection Nozzles

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.

Diesel injection system modelling. Methodology and application for a first-generation common rail system

Abstract This article details a method for modelling the most critical parts of an injection system. It focuses on the most important component of the system, the injector itself. As a clear example of this methodology, the modelling of a first-generation common rail injection system is carried out using a commercial code. The proposed methodology for modelling the injection system is based on two types of characterization: a detailed dimensional characterization and a hydraulic characterization of the different internal parts of the injector. The dimensional characterization is based on the use of a fine detail measuring technique applied to all the constituents of the injector. These include the passages and internal lines of the injector, internal volumes, calibrated orifices, nozzle springs, clearances between moving sections of pistons, etc. The second type of characterization makes reference mainly to the hydraulic characterization of the nozzle and injector control orifices, which together with dimensional information makes it possible to determine the discharge coe cient. In this case, special emphasis is placed on the detection of critical cavitation conditions and repercussions of this on the flow. This is a typical phenomenon in control orifices and also in nozzles subject to strong pressure gradients. Once the model is obtained, it is tested and validated. Following this, the values of the experimental injected mass and rate of injection at different operating points are compared with the model results.

Determination of Diesel sprays characteristics in real engine in-cylinder air density and pressure conditions

The present paper centers on the establishment of a quantified relationship between the macroscopic visual parameters of a Diesel spray and its most influential factors. The factors considered are the ambient gas density, as an external condition relative to the injection system, and nozzle hole diameter and injection pressure as internal ones. The main purpose of this work is to validate and extend the different correlations available in the literature to the present state of the Diesel engine, i.e. high injection pressure, small nozzle holes, severe cavitating conditions, etc. Five mono-orifice, axi-symmetrical nozzles with different diameters have been studied in two different test rigs from which one can reproduce solely the real engine in-cylinder air density, and the other, both the density and the pressure. A parametric study was carried out and it enabled the spray tip penetration to be expressed as a function of nozzle hole diameter, injection pressure and environment gas density. The temporal synchronization of the penetration and injection rate data revealed a possible explanation for the discontinuity observed as well by other authors in the spray’s penetration law. The experimental results obtained from both test rigs have shown good agreement with the theoretical analysis. There have been observed small but consistent differences between the two test rigs regarding the spray penetration and cone angle, and thus an analysis of the possible causes for these differences has also been included.

A Study of the Relation Between Nozzle Geometry, Internal flow and Sprays Characteristics in Diesel Fuel Injection Systems

This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed : one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.

Study of the influence of nozzle seat type on injection rate and spray behaviour

A deep analysis of the injection rate characteristics and spray behaviour of the most used nozzle types in diesel engines [microSAC and valve covered orifice (VCO)] has been carried out. In order to compare the injection characteristics and the spray behaviour of both nozzle types, several experimental installations were used, such as the steady flow test rig, injection rate test rig, spray momentum test rig, and nitrogen test rig, to obtain a full hydrodynamic and spray characterization. The study of the flow in both nozzles was analysed under steady flow conditions in the steady flow test rig and in real unsteady flow conditions in the injection rate test rig and the spray momentum test rig. The macroscopic properties of the spray (tip penetration and spray cone angle) were characterized using a high-pressure test rig. From the point of view of the internal flow behaviour, the results showed interesting differences in the permeability of both nozzle geometries, with a higher discharge coefficient in the microSAC nozzle. However, from the point of view of air entrainment, the results showed a better quality of fuel-air mixing in the VCO nozzle. Besides the evidence from the experimental results, a theoretical analysis was carried out in order to identify the most important parameters that determine the spray behaviour and thus justify the different macroscopic behaviour of both nozzles.

Understanding the Acoustic Oscillations Observed in the Injection Rate of a Common-Rail Direct Injection Diesel Injector

Measuring the rate of injection of a common-rail injector is one of the first steps for diesel engine development. The injected quantity as a function of time is of prime interest for engine research and modeling activities, as it drives spray development and mixing, which, in current diesel engines, control combustion. On the other hand, the widely used long-tube method provides results that are neither straightforward nor fully understood. This study, performed on a 0.09-mm axially drilled single-hole nozzle, is part of the Engine Combustion Network (ECN) and aims at analyzing the acoustic oscillations observed in the rate of injection signal and measuring their impact on the real injection process and on the results recorded by the experimental devices. Several tests have been carried out for this study, including rate of injection and momentum, X-ray phase-contrast of the injector, and needle motion or injector displacement. The acoustic analysis revealed that these fluctuations found their origin in the sac of the injector and that they were the results of an interaction between the fluid in the chamber (generally gases) or in the nozzle sac and the liquid fuel to be injected. It has been observed that the relatively high oscillations recorded by the long-tube method were mainly caused by a displacement of the injector itself while injecting. In addition, the results showed that these acoustic features are also present in the spray, which means that the oscillations make it out of the injector, and that this temporal variation must be reflected in the actual rate of injection.

Investigation of the Influence of Injection Rate Shaping on the Spray Characteristics in a Diesel Common Rail System Equipped with a Piston Amplifier

The quality of the mixing process of fuel and air in a direct injection diesel engine relies heavily on the way the spray develops when injected into the combustion chamber. Among other factors, the spray development depends on the injection rate of the fuel delivered by the injector. The paper presents a study, at both a macroscopic and microscopic level, of a Diesel spray generated by a common-rail injection system featuring a piston pressure amplifier. By modifying the timing and the duration of the injector and amplifier piston actuation, it is possible to obtain high injection pressures up to 180 MPa, and different shapes for the injection rate, which would not be achievable with a regular common rail injection system. The spray evolution produced by three different injection rate shapes (square, ramp, and boot) has been investigated in an injection test rig, by means of visualization and PDPA techniques, at different injection conditions. The main conclusions are the important effect on spray penetration of the initial injection rate evolution and the small influence of the maximum injection pressure attained at the end of the injection event. Smaller or even negligible effects have been found on the spray cone angle and on the droplet Sauter mean diameter.

Numerical Estimation of End Corrections in Extended-Duct and Perforated-Duct Mufflers

One-dimensional models for extended-duct and perforated-duct mufflers require the introduction of end corrections in order to account for multidimensional effects at the junctions. In this paper, a numerical two-dimensional finite element calculation has been used in order to obtain information on these end corrections. The results have been validated through comparison with experimental measurements performed with a modified version of the impulse method. Then, the influence of the different geometric characteristics of the mufflers on the end correction have been studied. A general correlation in terms of relevant nondimensional parameters is given for extended-duct mufflers, whereas for perforated mufflers a general correlation has not been obtained due to the eventual coupling with other attenuation mechanisms.

Flow regime effects over non-cavitating diesel injection nozzles

The research conducted and explained in this paper aims to explore and understand the influence of flow regime (laminar, transition or turbulent) inside diesel injector nozzles. For this purpose, an experimental study based on mass flow rate and momentum flux measurements on three convergent nozzles has been carried out. The combination of both types of measurement has been helpful to obtain information about the nature of the flow and its consequences on important variables, such as injection effective velocity and effective area of nozzle outlet orifices. As a main result of the investigation, and depending of the flow regime, a differentiated behaviour has been observed which was clearly reflected in the non-dimensional flow parameters defined and used through the study.