Coking Phenomena in Nozzle Orifices of Dl-Diesel Engines

Tang, Jens; Pischinger, Stefan; Lamping, Matthias; Körfer, Thomas; Tatur, Marek; Tomazic, Dean

doi:10.4271/2009-01-0837

Cited by 42 publications

(26 citation statements)

References 17 publications

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“…open); this is now the standard practice in manufacturing automotive diesel injector nozzles (Potz et al 2000); still, some cavitation may be needed as it is thought to make nozzles more resistant against deposit formation (Tang et al 2009). Cavitation is also known to decrease the nozzle flow rate (Soteriou et al 1995) and lead in some cases (but not always) to flow choking (Payri et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

et al. 2016

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efficiency of such engines. Among others, the fuel injection equipment (FIE) is a key component for improving the efficiency of environmentally friendly engines. Recent advances dictate the use of extra high injection pressures, of the order of 3000 bar and tiny flow passages (injection holes) of the order of 100-250 μm in diameter, for improved fuel atomisation and combustion efficiency. Under these circumstances, cavitation has been found to develop inside fuel injection nozzles at the early studies of Badock et al. (1999), Bergwerk (1959), Chaves et al. (1995) and Nurick (1976), followed by Arcoumanis et al. (2000), Blessing et al. (2003), Mitroglou et al. (2014) and Roth et al. (2002) in more realistic real-size nozzle geometries offering optical access; equally helpful studies performed in transparent enlarged nozzle replicas [selectively (Andriotis et al. 2008;Arcoumanis et al. 2000;Miranda et al. 2003; Mitroglou and Gavaises 2013;Powell et al. 2000)] also indicate that cavitation plays an increasingly significant role in the nozzle's internal flow structure and development. Cavitation inside an injection hole is believed to enhance spray atomisation, either directly through the implosion of cavitation bubbles or indirectly because it increases turbulence in the nozzle flow (Badock et al. 1999;Walther 2002); unfortunately, under certain circumstances induces erosion (Dular and Petkovšek 2015;Koukouvinis et al. 2016) that may lead to catastrophic failures. Moreover, cavitation inside the injection holes promotes shot-toshot spray instabilities (Mitroglou et al. 2011(Mitroglou et al. , 2012Suh and Lee 2008), which, in turn, are responsible for poor combustion efficiency and increased emissions (Hayashi et al. 2013). Two distinct macroscopic forms of cavitation have been identified, which are referred to as geometryinduced and vortex or 'string' cavitation. The former can be, partially or totally, suppressed by appropriate design of the inlet hole curvature and non-cylindrical injection hole Abstract The flow inside a purpose built enlarged singleorifice nozzle replica is quantified using time-averaged X-ray micro-computed tomography (micro-CT) and highspeed shadowgraphy. Results have been obtained at Reynolds and cavitation numbers similar to those of real-size injectors. Good agreement for the cavitation extent inside the orifice is found between the micro-CT and the corresponding temporal mean 2D cavitation image, as captured by the high-speed camera. However, the internal 3D structure of the developing cavitation cloud reveals a hollow vapour cloud ring formed at the hole entrance and extending only at the lower part of the hole due to the asymmetric flow entry. Moreover, the cavitation volume fraction exhibits a significant gradient along the orifice volume. The cavitation number and the needle valve lift seem to be the most influential operating parameters, while the Reynolds number seems to have only small effect for the range of values tested. Overall, the study demonstrates that use of micro-CT can ...

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Section: Introductionmentioning

confidence: 99%

Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

et al. 2016

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“…The deposits are thought to be formed as a remnant of the combustion process, as a result of residual fuel, particulates and vapours, and this would explain why the layers are thicker and more developed towards the outlet, where these components are all readily available [8,9]. Deposition has occurred all the way into the minisac of the CD DU injector.…”

Section: Deposit Morphologymentioning

confidence: 99%

“…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%

“…In analysis of a cross-sectioned diesel injector from a medium-duty truck engine, Tang et al showed the deposit composition changed through the cross-section; in particular zinc appeared to be concentrated close to the metal surface of the nozzle and the deposit became more carbonaceous away from the metal interface as it grew thicker [9]. Variation in chemical composition through the deposit indicates that the deposit may form an initiation layer followed by a thicker secondary layer on top, in a growth mechanism which might not be uniform across the length of the injector nozzle.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Ultimately, external deposits lead to a deterioration of combustion efficiency, a decrease in rated power and cause a rise in brake specific fuel consumption [5]. The formation of coking deposits is driven by higher temperatures at the nozzle and in its spray holes, while cavitation inside the nozzle serves as an inhibitor to their built-up [6] [7]. Cavitation inside the nozzle induced by a lower discharge coefficient proved to be beneficial against coking.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of Control Piston Motion and Pressure Inside of a Common Rail Diesel Injector

Schuckert

Wachtmeister

2017

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

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In this paper the experimental setup of a commercial third generation common rail solenoid injector with advanced measurement is discussed. The motion of the control piston is measured while performing injection rate investigations using a purpose-built injection rate analyzer of the Bosch type. At the same time fuel pressure in the feed line of the nozzle is gauged and contrasted to fuel pressure before the inlet connector. In contrast to the steady rise observed in a similar study, the motion of the control piston in this case is characterized by a changing gradient in the upward movement. The magnitude of the negative displacement of the upper part of the control piston due to the fuel pressure in the control volume corresponds to simulation results of the elastic deformation. Pressure before the inlet connector and pressure in the feed line exhibit a similar course with a difference in magnitude that is rising with higher rail pressures. Precisely with the end of injection the pressure in the feed line surpasses the pressure before the inlet connector for a short moment. The measurement results of control piston motion and pressure inside the injector are of particular interest because these parameters are to serve as indicators for changes in the injection rate caused by phenomena like wear and coking amongst others.Keywords common rail injector, injection rate measurement, eddy current sensor, control piston motion, feed line pressure IntroductionThe act of injecting diesel not only supplies the fuel for the subsequent combustion, but at the same time also determines the start of combustion with the diesel combustion process. This is unlike the gasoline combustion process, where injection and ignition are separated. Thus, the injection process is a major influence factor to consider in order complying with the increasingly severe emission legislation for compression ignition engines. Furthermore, alterations affecting the injection parameters of common rail diesel injectors that emerge during engine operation have been identified. Research efforts focused on brittle external nozzle deposits mostly consisting of carbon referred to as coking. In recent years, a type of sticky, the so-called internal diesel injector deposits (IDID) have appeared in production engines and caused needles to stick in common rail diesel injectors. It has been observed that the addition of certain additives (polyisobutylene succinimide; PIBSI) to diesel fuel, which are to inhibit the formation of coking deposits, have the side effect of contributing to the formation of IDID [1] [2]. These PIBSI react with acids that emerge from fatty acid methyl ester (FAME), a biodiesel supplement to common diesel in the European Union, to form IDID. Other major factors that influence the occurrence of IDID are high fuel temperatures and the content of aromatics and oxygen in the diesel fuel [2]. Deposits on the nozzle tip and inside the nozzle holes due to coking cause numerous adverse effects. It is proven that this type of deposits exe...

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Coking Phenomena in Nozzle Orifices of Dl-Diesel Engines

Cited by 42 publications

References 17 publications

Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

Application of X-ray micro-computed tomography on high-speed cavitating diesel fuel flows

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

Characteristics of Control Piston Motion and Pressure Inside of a Common Rail Diesel Injector

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