José V. Pastor

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

Diesel spray image segmentation with a likelihood ratio test

To characterize the macroscopic behavior of Diesel sprays and to validate and extend for current high-pressure injection systems the correlations existent in the literature, it is necessary to determine the spray geometry accurately, at least in terms of spray tip penetration and cone angle. These parameters are measured by analyzing Diesel spray images and are highly sensitive to the correct edge determination. An algorithm for segmentation of color images based on a likelihood ratio test is presented. This algorithm is compared with others available in the literature and has been validated, even for adverse experimental conditions. The experimental facilities, optical layouts, and image-processing algorithms are described.

Contribution to the application of two-colour imaging to diesel combustion

The two-colour method (2C) is a well-known methodology for the estimation of flame temperature and the soot-related KL factor. A 2C imaging system has been built with a single charge-coupled device (CCD) camera for visualization of the diesel flame in a single-cylinder 2-stroke engine with optical accesses. The work presented here focuses on methodological aspects. In that sense, the influence of calibration uncertainties on the measured temperature and KL factor has been analysed. Besides, a theoretical study is presented that tries to link the true flame temperature and soot distributions with those derived from the 2C images. Finally, an experimental study has been carried out in order to show the influence of injection pressure, air density and temperature on the 2C-derived parameters. Comparison with the expected results has shown the limitations of this methodology for diesel flame analysis.

Planar Laser-Induced Fluorescence fuel concentration measurements in isothermal Diesel sprays

This paper presents a complete methodology to perform fuel concentration measurements of Diesel sprays in isothermal conditions using the Planar Laser-Induced Fluorescence (PLIF) technique. The natural fluorescence of a commercial Diesel fuel is used with an excitation wavelength of 355 nm. The correction and calibration procedures to perform accurate measurements are studied. These procedures include the study of the fluorescence characteristics of the fuel as well as the correction of the laser sheet non-homogeneities and the losses due to Mie scattering, absorption and autoabsorption. The results obtained are compared with theoretical models and other experimental techniques.

Segmentation of diesel spray images with log-likelihood ratio test algorithm for non-Gaussian distributions

A methodology for processing images of diesel sprays under different experimental situations is presented. The new approach has been developed for cases where the background does not follow a Gaussian distribution but a positive bias appears. In such cases, the lognormal and the gamma probability density functions have been considered for the background digital level distributions. Two different algorithms have been compared with the standard log-likelihood ratio test (LRT): a threshold defined from the cumulative probability density function of the background shows a sensitive improvement, but the best results are obtained with modified versions of the LRT algorithm adapted to non-Gaussian cases.

Analysis of calibration techniques for laser-induced incandescence measurements in flames

In order to obtain quantitative soot concentration results in flames using laser-induced incandescence (LII), different correction and calibration procedures are needed. In this work, two different calibration methodologies were applied to a laminar diffusion flame in order to obtain the most suitable calibration procedure for sooting conditions. First, a series of spatially resolved light extinction measurements were implemented and correlated to the laser-induced incandescence measurements under the same experimental conditions. Second, one single-point light extinction and the same laser-induced incandescence measurement were used to calculate a calibration constant for LII measurements by implementing an iterative method. Some correction routines have been performed to the data due to the non-homogeneities in the laser sheet, attenuation of the laser and attenuation of the incandescence signal itself due to the soot between the measurement plane and the detection system. Finally, an analysis of its applicability in real flames is detailed.

Experimental facility and methodology for systematic studies of cold startability in direct injection Diesel engines

Cold start at low temperatures in current direct injection (DI) Diesel engines is a problem which has not yet been properly solved and it becomes particularly critical with the current trend to reduce the engine compression ratio. Although it is clear that there are some key factors whose control leads to a proper cold start process, their individual relevance and relationships are not clearly understood. Thus, efforts on optimization of the cold start process are mainly based on a trial-and-error procedure in climatic chambers at low ambient temperature, with serious limitations in terms of measurement reliability during such a transient process, low repeatability and experimental cost. This paper presents a novel approach for an experimental facility capable of simulating real engine cold start, at room temperature and under well-controlled low speed and low temperature conditions. It is based on an optical single cylinder engine adapted to reproduce in-cylinder conditions representative of those of a real engine during start at cold ambient temperatures (of the order of −20 °C). Such conditions must be realistic, controlled and repeatable in order to perform systematic studies in the borderline between ignition success and misfiring. An analysis methodology, combining optical techniques and heat release analysis of individual cycles, has been applied.

Study of the steady flow produced by direct injection diesel engine intake ports

Abstract In this paper laser Doppler anemometry is used to characterize the steady flow field inside the cylinder generated by the two intake ports of a four-valve diesel head over the whole valve lift range and to compare the patterns at two different sections commonly used for global characterization in order to decide which is more appropriate for cylinder head evaluation. A more detailed investigation is performed for two valve lifts where the change in the flow patterns is more evident by applying a spectral analysis with the local normalized slotting technique to study the turbulent structures accompanying the in-cylinder swirl development.

Schlieren Methodology for the Analysis of Transient Diesel Flame Evolution

This work was partially funded by the Spanish Ministry of Education and Science through the “LES METHODS FOR THE SIMULATION OF MULTIPHASE SPRAYS” project (ENE2010-18542). Mr. Francisco J. Briceno wishes to acknowledge financial support through a PhD studies grant (AP2008-02231) also sponsored by the Spanish Ministry of Education and Science

Correction method for droplet sizing by laser-induced fluorescence in a controlled test situation

The linear sizing technique is used to evaluate the accuracy of a new correction strategy to limit scattering matters. The ratio of the elastic scattered light with fluorescence emission over monodispersed microspheres homogenously mixed in water is measured. Three cells filled with different concentrations of these fluorescent particles are illuminated with a thin laser beam that is moved inside the cell from the front to the back. A comparison of the linear sizing technique with and without correction is presented and shows that the correction enables the measurement of higher concentrations; the limits of the correction method are also shown. These results could be a potential step to apply this technique to sprays.