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Crua, Cyril
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Visual Analyses of End of Injection Liquid Structures and the Behaviour of Nozzle Surface-Bound Fuel in a Direct Injection Diesel Engine

BP International Ltd.-Martin Gold, Richard Pearson
University of Brighton-Dan Sykes, Guillaume de Sercey, Cyril Crua
Published 2019-01-15 by SAE International in United States
For efficiency, the majority of modern diesel engines implement multiple injection strategies, increasing the frequency of transient injection phases and thus, end of injection (EOI) events. Recent advances in diagnostic techniques have identified several EOI phenomena pertinent to nozzle surface wetting as a precursor for deposit formation and a potential contributor towards pollutant emissions. To investigate the underlying processes, highspeed optical measurements at the microscopic scale were performed inside a motored diesel engine under low load/idling conditions. Visualisation of the injector nozzle surface and near nozzle region permitted an indepth analysis of the post-injection phenomena and the behaviour of fuel films on the nozzle surface when the engine is not fired. Inspection of the high-speed video data enabled an interpretation of the fluid dynamics leading to surface wetting, elucidating the mechanisms of deposition and spreading. As the needle re-seated, the abrupt pressure drop inhibited atomisation. Large, slow moving, liquid structures were released into the cylinder with the capability of impinging on nearby surfaces, creating localised fuel rich regions, or escaping through the exhaust and contributing…
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Simulation and Measurement of Transient Fluid Phenomena within Diesel Injection

SAE International Journal of Advances and Current Practices in Mobility

BP International Ltd.-Martin Gold, Richard Pearson
City University London-Mithun Murali-Girija, Foivos Koukouvinis, Manolis Gavaises
  • Journal Article
  • 2019-01-0066
Published 2019-01-15 by SAE International in United States
Rail pressures of modern diesel fuel injection systems have increased significantly over recent years, greatly improving atomisation of the main fuel injection event and air utilisation of the combustion process. Continued improvement in controlling the process of introducing fuel into the cylinder has led to focussing on fluid phenomena related to transient response. High-speed microscopy has been employed to visualise the detailed fluid dynamics around the near nozzle region of an automotive diesel fuel injector, during the opening, closing and post injection events. Complementary computational fluid dynamic (CFD) simulations have been undertaken to elucidate the interaction of the liquid and gas phases during these highly transient events, including an assessment of close-coupled injections.Microscopic imaging shows the development of a plug flow in the initial stages of injection, with rapid transition into a primary breakup regime, transitioning to a finely atomised spray and subsequent vaporisation of the fuel. During closuring of the injector the spray collapses, with evidence of swirling breakup structures together with unstable ligaments of fuel breaking into large slow-moving droplets. This leads to…
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High-Speed Microscopic Imaging of the Initial Stage of Diesel Spray Formation and Primary Breakup

BP Global Fuels Technology-Martin Gold, Cassandra Higham
University of Brighton-Cyril Crua, Tenzin Shoba, Morgan Heikal
Published 2010-10-25 by SAE International in United States
The formation and breakup of diesel sprays was investigated experimentally on a common rail diesel injector using a long range microscope. The objectives were to further the fundamental understanding of the processes involved in the initial stage of diesel spray formation.Tests were conducted at atmospheric conditions and on a rapid compression machine with motored in-cylinder peak pressures up to 8 MPa, and injection pressures up to 160 MPa. The light source and long range imaging optics were optimized to produce blur-free shadowgraphic images of sprays with a resolution of 0.6 μm per pixel, and a viewing region of 768x614 μm. Such fine spatial and temporal resolutions allowed the observation of previously unreported shearing instabilities and stagnation point on the tip of diesel jets. The tip of the fuel jet was seen to take the shape of an oblate spheroidal cap immediately after leaving the nozzle, due to the combination of transverse expansion of the jet and the physical properties of the fuel. The spheroidal cap was found to consist of residual fuel trapped in the…
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Laser-Induced Fluorescence Investigation of Nitric Oxide Formation and Hydroxyl Radicals in a Diesel Rapid Compression Machine

University of Brighton-Romain Demory, Cyril Crua, Morgan Heikal
Published 2010-05-05 by SAE International in United States
The research presented here aims at providing a deeper understanding of the formation of nitric oxide in diesel combustion. To this end, in-cylinder distributions of nitric oxide (NO) were acquired by laser-induced fluorescence (LIF) in a rapid compression machine at conditions representative of a modern diesel passenger vehicle. In particular, the effects of injection and in-cylinder pressure on NO formation were investigated temporally and spatially to offer new insight into the formation of NO. Excitation and collection strategies were notably fine-tuned to avoid the collection of spurious signal due to oxygen (O₂) fluorescence. NO fluorescence was first recorded slightly after the onset of the diffusion flame and until late in the expansion stroke. The early low levels of NO were located on the lean side of the high density of hydroxyl radicals (OH). The absence of NO inside the flame plume could however not be investigated because of the severe attenuation of the laser light attributed to hot CO₂ molecules, intermediate species and soot. The formation rate of nitric oxide was found almost constant during…
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PDA Characterisation of Dense Diesel Sprays Using a Common-Rail Injection System

Ricardo Consulting Engineers-Martin Gold
University of Brighton - UK-Julien Lacoste, Cyril Crua, Morgan Heikal, Dave Kennaird
Published 2003-10-27 by SAE International in United States
To meet the future low emission targets for Diesel engines, engineers are optimising both the fuel injection and after treatment systems fitted to Diesel engines. In order to optimise the fuel injection system there is a need to characterize the fuel spray for a given injection nozzle geometry and injection pressure/duration. Modern Diesel common rail systems produce very dense sprays, making in-cylinder investigation particularly difficult. In this study the measurement of droplet sizes and velocities in dense Diesel sprays has been investigated using Phase Doppler Anemometry (PDA). PDA has been proven to be a valuable technique in providing an understanding of the structure and characteristics of liquid sprays in many studies. It is often applied to finely atomised and dispersed particle flows. However, the application of PDA to dense sprays is complex and therefore the measurements reported in the literature are performed under conditions that are not representative of modern Diesel engines.This paper reports both on the processes undertaken to optimise a classic PDA system so that it may be used to gather data in…
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