2011

The spray formation and breakup of fossil diesel, biodiesel (RME) and kerosene was investigated experimentally on a common rail diesel injector using a long working distance microscope. The objectives were to further the fundamental understanding of the processes involved in the initial stage of diesel spray formation, and the influence of viscosity, lubricity and surface tension. Tests were conducted at atmospheric conditions and on a rapid compression machine. Analysis of the fuel sprays at the start of injection revealed jets for each fuel whose morphology was governed by their Reynolds and Weber numbers. As the fuel viscosity was one of the most varying properties this produced jets that were dynamically different. The differences were also reflected in the injection timing of the fuel sprays where the friction between the fluid and the nozzle wall controlled the start of injection (SOI). Kerosene was found to advance the SOI when compared to the diesel and as such suspected to have an impact on the combustion phasing. The RME results fully corroborated with the conclusions drawn based on kerosene. Downstream from the nozzle the stabilising effect of viscosity can be seen to reduce the formation of surface waves, ligaments and droplets prior to the reaching the breakup length. It is speculated that the liquid core of the RME jet does not generally breakup directly into ligaments and droplets, but transitions into liquid sheets which then breakup or recombine into ligaments through surface tension.

Fuel, 2007

Spray formation from diesel fuel injection through a realistic heavy-duty multi-hole common rail injector is studied in a newly developed high pressure, high temperature cell, using digital high speed shadowgraphy at 4500 frames per second. Care is taken to establish accurate synchronisation between camera and injection system and because of the relatively large exposure time, an effective camera image time is calculated for every frame. Further emphasis is given to determining the actual start of fuel mass injection by comparing (for each injection) a predetermined, rail pressure dependent needle relaxation distance to the actual needle lift signal. The spatiotemporal evolution of the spray is found to reproduce well in general, but often sprays suffer from short-lived, small, laterally moving anomalies, which influence axial motion and the spray cone angle. High speed shadowgraphy allows this to be observed and taken into account. After an overview of methods found in the literature, an algorithm for geometrical analysis is presented, which is based on an extension of a combination of those methods. In this algorithm, a local spray angle # i (x) is determined from lateral cross-sections at 80% of the shadow level in order to encompass most of the spray without being too sensitive to background noise. The macroscopic cone angle # cone is derived from the approximate constancy of # i (x) over a relatively long axial distance. Spray penetration is obtained by lateral integration of the spray shadow. A procedure for accurate correlation of spray growth with time shows that the growth is proportional to t b with b = 0.57 ± 0.02 for a common rail pressure of 150 MPa and a gas density 33 kg/m 3 (N 2 at room temperature). The exact value of b is very sensitive to uncertainties in synchronisation and the start of injection determination. The spray cone angle # cone is not constant, but varies with time during an injection, mainly as a result of spray shape changes.

This paper presents an imaging-based diagnostic technique to quantify the pulse-to-pulse variability of macroscopic fuel spray characteristics for Direct-Injection Spark-Ignition (DISI) engine applications. The analysis approach is based on the construction of a spray ensemble image, reflecting the regions of probability of liquid presence for a set of images. Overlaying of an individual spray boundary on the probability-based ensemble image can further enhance the twodimensional visualization of the pulse-to-pulse spray variations.

Fuel, 2012

2012). The characterisation of diesel nozzle flow using high speed imaging of elastic light scattering. Fuel,

Measurement Science and Technology, 2012

A high-speed imaging system capable of acquiring Planar Laser Induced Fluorescence (PLIF) images and Mie scattering images in a near-simultaneous fashion has been developed. Acquiring both LIF and Mie images enables the liquid phase to be discriminated from the vapor phase. High-speed imaging allows the temporal evolution of flow structures to be evaluated. Images of sprays from a multi-hole Diesel fuel injector operating under engine-like conditions were acquired. The vapor phase images reveal intricate fluid dynamic structures that exhibit a high degree of variability.

Sensors

This paper proposes a sensor system for an internal combustion engine based on a new vision-based algorithm supported by the Schlieren sensorization technique, which allows to acquire the macroscopic parameters of the fuel spray injected in a reciprocating internal combustion engine under unmanned aerial vehicle-like conditions. The sensor system proposed here is able to automatically determine the spray cone angle, its area and its penetration. In addition, the external surface and the volume of the fuel spray is estimated together with the injector opening delay and the ignition delay. The developed algorithm was experimentally tested using a conventional diesel fuel in a single-cylinder engine with an optically adapted head but with easy application and other configurations of reciprocating internal combustion engines. These spray macroscopic parameters allow to analyze, among others, the effect of the spray on the development of both the injection and combustion processes under ...

2015

The analysis of diesel sprays in engine-like conditions is of fundamental importance for the study and development of diesel engines. Laser diffraction techniques were used in this work to study droplet size distribution of a diesel spray injected into a constant-volume combustion vessel with line-of-sight optical access. The experiments were conducted using a common rail injector electronically controlled to inject after the combustion of a stoichiometric air-methane mixture. This allowed to reach temperature of around 1000 K and pressure of more than 10 bar. In the first stage of the work back-light technique was employed to measure spray characteristics such as penetration and cone angle. The liquid phase behavior was highlighted by means of a high-speed digital camera for different values of injection duration and pressure. In the second phase particle size distribution and pertinent attributes of the distribution were measured on the spray axis at 10 mm from the injector orific...

International Journal of Spray and Combustion Dynamics, 2018

This paper reports on the spray structure of the biofuels, ethanol, and butanol generated by a multihole direct-injection spark-ignition injector, which is studied in a constant volume chamber. The spray shape and structure are analyzed using two-phase structured laser illumination planar imaging where both laser-induced fluorescence and Mie-scattering light are recorded simultaneously for the extraction of instantaneous laser-induced fluorescence/Mie-scattering ratio images. Quantitative planar measurements of the droplet Sauter mean diameter are conducted, using calibration data from phase-Doppler anemometry. The resulting Sauter mean diameters are presented for ethanol and butanol at various fuel temperatures at different times after the start of injection. It is found that an increase in fuel temperature results in a faster atomization and higher evaporation rate, which leads to reduced spray tip penetration and smaller droplet Sauter mean diameter. At equivalent conditions, butanol consistently showed larger spray tip penetration in comparison to ethanol. This behavior is due to the higher surface tension and viscosity of butanol resulting in the formation of larger droplets and larger Sauter mean diameters in the whole spray region. Finally, the butanol injection also shows larger cyclic variations in the spray shape from injection to injection which is explained by the internal nozzle flow that is influenced by larger fuel viscosity as well. The Sauter mean diameter distribution is also compared to phase-Doppler anemometry data showing good agreement and an uncertainty analysis of the structured laser illumination planar imaging-laser-induced fluorescence/Mie-scattering technique for planar droplet sizing in direct-injection spark-ignition sprays is presented.

International Journal of Engine Research, 2019

An investigation of the interaction between the in-cylinder flow and the spray topology in two spray-guided direct injection optical engines is reported. The bulk flow field in the combustion chamber is characterized using particle image velocimetry. Geometrical parameters such as the axial penetration and the spray angle of the liquid spray are measured using Mie scatter imaging and/or diffuse back-illumination. The measured parameters are compared with data from a constant volume chamber available in the literature. For a late injection strategy, the so-called ECN Spray G standard condition, the mean values of the spray penetration do not seem to be significantly perturbed by the in-cylinder flow motion until the plumes approach the piston surface. However, spray probability maps reveal that cycle-to-cycle fluctuations of the spatial distribution of the liquid spray are affected by the magnitude of the in-cylinder flow. Particle image velocimetry during injection shows that the fl...

2019

In order to comply with the current and future emission norms applicable to diesel engines, understanding the fuel-air mixing phenomena in depth is quite crucial. Fuel spray inside the cylinder of an engine in operation interacts with in-cylinder gases as well as with solid boundaries. Fuel spray impinging on the cylinder wall and piston top, may subsequently enhance soot formation and hence, study and analysis of fuel spary characteristics can help to minimize these effects. However, study of the physics of spray evolvement and dynamics demands advanced diagnostics and numerical techniques. Many attempts have been made in developing computational models for analyzing the fuel-air and fuel-wall interactions. Despite those efforts it remains an exciting area of research to accurately model the spray behavior under dynamic conditions inside the engine cylinder. These models need continuous inputs from experimental studies for validation and for further development purposes. For experi...