Deposit Formation in the Holes of Diesel Injector Nozzles: A Critical Review

Birgel, Andreas; Ladommatos, Nicos; Aleiferis, P.G.; Zülch, Stefan; Milovanović, Nebojša; Lafon, V.; Orlović, Aleksandar M.; Lacey, Paul I.; Richards, Paul

doi:10.4271/2008-01-2383

Cited by 71 publications

(49 citation statements)

References 40 publications

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“…Shifts towards piezo-actuated injectors mean that dynamic response times are improved, reducing the time spent in the transient injection phase. This has been shown to give superior fuel air mixing when compared with older systems using solenoid actuated injectors [5,6]. A more recent technique in injection optimisation utilises split injection strategies.…”

Section: Introductionmentioning

confidence: 99%

“…This reduction in performance is known to manifest in a variety of ways including increased acoustic and pollutant emissions [1][2][3]. The deposits can also reduce the hydraulic diameter of the nozzle hole, resulting in a reduction in the quantity of injected fuel and reduced quality and consistency of injection [3][4][5]; all of which cause a reduction in engine power [6]. The deposits can also increase cavitation, which can then lead to further coking of the nozzle [7].…”

Section: Introductionmentioning

confidence: 99%

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A quantitative analysis of nozzle surface bound fuel for diesel injectors

Turner

Sykes

Sercey

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

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In a fuel injector at the end of the injection, the needle descent and the rapid pressure drop in the nozzle leads to discharge of large, slow-moving liquid structures. This unwanted discharge is often referred as fuel 'dribble' and results in near-nozzle surface wetting, creating fuel-rich regions that are believed to contribute to unburnt hydrocarbon emissions. Subsequent fluid overspill occurs during the pressure drop in the expansion stroke when residual fluid inside the nozzle is displaced by the expansion of trapped gases as the pressure through the orifices is equalised, leading to further surface wetting. There have been several recent advancements in the characterisation of these near nozzle fluid processes, yet there is a lack of quantitative data relating the operating conditions and hardware parameters to the quantity of overspill and surface-bound fuel. In this study, methods for quantifying nozzle tip wetting after the end of injection were developed, to gain a better understanding of the underlying processes and to study the influence of engine operating conditions. A high-speed camera with a longdistance microscope was used to visualise fluid behaviour at the microscopic scale during, and after, the end of injection. In order to measure the nozzle tip temperature, a production injector was used which was instrumented with a type K thermocouple near one of the orifices. Image post-processing techniques were developed to track both the initial fuel coverage area on the nozzle surface, as well as the temporal evolution and spreading rate of surface-bound fluid. The conclusion presents an analysis of the area of fuel coverage and the rate of spreading and how these depend on injection pressure, in-cylinder pressure and in-cylinder temperature. It was observed that for this VCO injector, the rate of spreading correlates with the initial area of fuel coverage measured after the end of injection, suggesting that the main mechanism for nozzle wetting is through the impingement of dribble onto the nozzle. However, occasional observations of the expansion of orifice-trapped gas were made that lead to a significant increase in nozzle wetting. KeywordsDiesel; end of injection; dribble; surface wetting; image processing Introduction Increasingly strict emissions standards place considerable pressure on the automotive industry to increase the efficiency of, and reduce the emissions of the engine. This is primarily done by optimising the fuel-air mixing processes that occur inside the combustion chamber. Since the fuel air mixing is affected by the fuel injection equipment (FIE), much of the research efforts have been in improving the injector design and spray characteristics. This has resulted in the numbers of holes in the injector tip increasing with subsequent designs, as well as increases in the operating pressure, with typical systems operating with common rail pressures of over 200 MPa. These increasingly harsh conditions are believed to accelerate the formation and growth of deposits in and arou...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A quantitative analysis of nozzle surface bound fuel for diesel injectors

Turner

Sykes

Sercey

et al. 2017

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems

View full text Add to dashboard Cite

show abstract

“…This confirms that the volume of fuel that makes up the spheroidal cap can exist as trapped fuel in the orifice of the nozzle. The possibility of fuel being stored in the injector holes after the end of the injection process has been discussed in [20] and [21], and is believed to contribute to the formation of deposits in the nozzle orifices.…”

Section: Resultsmentioning

confidence: 99%

High-Speed Microscopic Imaging of the Initial Stage of Diesel Spray Formation and Primary Breakup

Crua¹,

Shoba²,

Heikal³

et al. 2010

SAE Technical Paper Series

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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 optimised to produce blur-free shadowgraphic images of sprays with a resolution of 0.6 µm per pixel, and a viewing region of 768×614 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 injector hole after the end of the injection process. The formation of fuel ligaments close to the orifice was also observed, ligaments which were subsequently seen to breakup into droplets through hydrodynamic and capillary instabilities.An ultra-high speed camera was then used to capture the dynamics of the early spray formation and primary breakup with fine temporal and spatial resolutions. The frame rate was up to 5 million images per second and exposure time down to 20 ns, with a fixed resolution of 1280×960 pixels covering a viewing region of 995×746 µm. A vortex ring motion within the vapourised spheroidal cap was identified, and resulted in a slipstream effect which led to a central ligament being propelled ahead of the liquid jet.

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“…Additionally the high temperatures in the engine, when thermally conducted along the injector, will likely act as an accelerant to deposit formation. It is generally observed that higher engine temperatures increase deposit severity [6,8,9,12].…”

Section: Deposit Morphologymentioning

confidence: 99%

A Chemical and Morphological Study of Diesel Injector Nozzle Deposits - Insights into their Formation and Growth Mechanisms

Rounthwaite

Williams

McGivery

et al. 2017

SAE Int. J. Fuels Lubr.

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Modern diesel passenger car technology continues to develop rapidly in response to demanding emissions, performance, refinement, cost and fuel efficiency requirements. This has included the implementation of high pressure common rail fuel systems employing high precision injectors with complex injection strategies, higher hydraulic efficiency injector nozzles and in some cases <100µm nozzle hole diameters. With the trend towards lower diameter diesel injector nozzle holes and reduced cleaning through cavitation with higher hydraulic efficiency nozzles, it is increasingly important to focus on understanding the mechanism of diesel injector nozzle deposit formation and growth. In this study such deposits were analysed by cross-sectioning the diesel injector along the length of the nozzle hole enabling in-depth analysis of deposit morphology and composition change from the inlet to the outlet, using state-of-the-art electron microscopy techniques. Deposits produced in the injector nozzles of the industry standard fouling test (CEC F-98-08 DW10B bench engine) were compared with those formed in a vehicle driven on a chassis dynamometer, using a drive cycle more representative of real world vehicle conditions, to explore the effects of differing drive cycles and engine technologies. Fouling in all tests was accelerated with the addition of 1ppm zinc neodecanoate, as specified in the CEC DW10B test. This in-depth characterisation revealed a complex multi-layered system of deposits inside the diesel injector nozzle. Through analysing these layers the mechanisms enabling the initial deposit formation and growth can be postulated.

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Deposit Formation in the Holes of Diesel Injector Nozzles: A Critical Review

Cited by 71 publications

References 40 publications

A quantitative analysis of nozzle surface bound fuel for diesel injectors

A quantitative analysis of nozzle surface bound fuel for diesel injectors

High-Speed Microscopic Imaging of the Initial Stage of Diesel Spray Formation and Primary Breakup

A Chemical and Morphological Study of Diesel Injector Nozzle Deposits - Insights into their Formation and Growth Mechanisms

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