The influence of eccentric needle movement on internal flow and injection characteristics of a multi-hole diesel nozzle

Wang, Chuqiao; Moro, Adams; Xue, Fuying; Wu, Xinzhen

doi:10.1016/j.ijheatmasstransfer.2017.10.057

Cited by 31 publications

(13 citation statements)

References 37 publications

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“…Various types of geometric cavitation in diesel injectors have been studied experimentally 15–17 and theoretically 18–20 in recent decades, which indicates that cavitating flows inside diesel nozzles were influenced by many factors, such as the nozzle geometry, 21–23 fuel thermodynamic properties, 24–26 injection or backpressure conditions 27–29 and needle motion. 5,30,31 However, few studies have been done on string cavitation. Arcoumanis and colleagues 15,18,32 conducted cavitation flow on optical experiments.…”

Section: Introductionmentioning

confidence: 99%

Visual experimental investigations of string cavitation and residual bubbles in the diesel nozzle and effects on initial spray structures

Guo

Zhang

et al. 2018

International Journal of Engine Research

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In this article, optical experiments on string cavitation and residual bubbles inside the real-size transparent tapered diesel nozzle and near-nozzle spray structures were performed based on a high-pressure common rail fuel injection system with a high-speed camera. The tapered nozzle which has high flow efficiency with weak or even no geometric cavitation has been widely used in commercial injectors, while there still exists string cavitation which may also influence the in-nozzle flow and subsequent spray. This article put focus on the tapered nozzle and the result indicated that the in-nozzle string cavitation provided a reasonable explanation for the two bumps of spray cone angles during the opening and closing stages of needle of real diesel engine injection processes. The suction and compression of air bubbles at the start and end stages of injection processes, and the various shot-to-shot near-nozzle spray patterns were captured and analyzed. These different near-nozzle spray patterns were attributed to the distribution of residual bubbles inside the nozzle orifice. The residual bubbles were survived from the last injection or sucked into the nozzle during needle opening stages. Stagnant bubbles were compressed and then accelerated the residual fuel which was close to the injector tip, leading to the formation of mushrooms. This study confirmed that the initial mushroom and the tail were generated by the interactions between the residual/sucked bubbles and the residual/initial fuel, and the leading mushroom was incurred by the combination of the transverse expansion of the jet and the laminar layer theory. This work pointed out and analyzed the new sources of the cycle-to-cycle variation of air/fuel mixture and spray.

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Section: Introductionmentioning

confidence: 99%

Visual experimental investigations of string cavitation and residual bubbles in the diesel nozzle and effects on initial spray structures

Guo

Zhang

et al. 2018

International Journal of Engine Research

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“…The minimal distance between the needle and the injector body was 20 µm. A similar approach was proven to give good results in [23,34].…”

Section: Simulation Set-upmentioning

confidence: 94%

Effect of the In-Cylinder Back Pressure on the Injection Process and Fuel Flow Characteristics in a Common-Rail Diesel Injector Using GTL Fuel

et al. 2021

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The presented paper aims to study the influence of mineral diesel fuel and synthetic Gas-To-Liquid fuel (GTL) on the injection process, fuel flow conditions, and cavitation formation in a modern common-rail injector. First, the influence on injection characteristics was studied experimentally using an injection system test bench, and numerically using the one-dimensional computational program. Afterward, the influence of fuel properties on internal fuel flow was studied numerically using a computational program. The flow inside the injector was considered as multiphase flow and was calculated through unsteady Computational Fluid Dynamics simulations using a Eulerian–Eulerian two-fluid approach. Finally, the influence of in-cylinder back pressure on the internal nozzle flow was studied at three distinctive back pressures. The obtained numerical results for injection characteristics show good agreement with the experimental ones. The results of 3D simulations indicate that differences in fuel properties influence internal fuel flow and cavitation inception. The location of cavitation formation is the same for both fuels. The cavitation formation is triggered regardless of fuel properties. The size of the cavitation area is influenced by fuel properties and also from in-cylinder back pressure. Higher values of back pressure induce smaller areas of cavitation and vice versa. Comparing the conditions at injection hole exit, diesel fuel proved slightly higher average mass flow rate and velocities, which can be attributed to differences in fluid densities and viscosities. Overall, the obtained results indicate that when considering the injection process and internal nozzle flow, GTL fuel can be used in common-rail injection systems with solenoid injectors.

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“…For asymmetric single-hole fuel injectors (where the interactions between nozzle holes are non-existent), it is possible for string cavitation to occur under eccentric sac/needle configuration 15,17,21,22 at low needle lift. This tendency of string cavitation to occur in the sac under low needle lift condition has been documented by various studies, [16][17][18]20,23,24 but the mechanism behind its occurrence is still unclear. Although it is strongly indicated that string cavitation occurrence is caused by strong vortex ring flow in the sac, accurate measurement of the three-dimensional (3D) velocity field in the sac has not been available yet.…”

Section: Introductionmentioning

confidence: 90%

“…This complex flow structure is mainly caused by the interactions between the nozzle holes 14,15 as well as needle eccentricity and needle lift on the internal flow of the sac. [17][18][19][20][21][22][23] The effects of needle lift and needle eccentricity on string cavitation existence are particularly important. For asymmetric single-hole fuel injectors (where the interactions between nozzle holes are non-existent), it is possible for string cavitation to occur under eccentric sac/needle configuration 15,17,21,22 at low needle lift.…”

Section: Introductionmentioning

confidence: 99%

“…This is because of the difficulties associated with visualization of internal flow in diesel injectors, such as the small sac size and very fast flow velocity. As a substitute, studies have turned to either using numerical simulation to explain about the origin of string cavitation 17,18,23,25 or carry out twodimensional (2D) particle image velocimetry (PIV). 16,20 This study aims to reveal the mechanism behind string cavitation occurrence at low needle lift.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Three-dimensional flow structure and string cavitation in a fuel injector and their effects on discharged liquid jet

Prasetya

Sou

Oki

et al. 2019

International Journal of Engine Research

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Two kinds of cavitation may occur in mini-sac type diesel injectors. The first is geometrical cavitation, which can usually be seen as a film-like structure in the nozzle. The second is the filament-like string cavitation. Both types of cavitation are known to affect fuel spray characteristics, although the effects of geometrical cavitation and that of string cavitation have not been individually clarified. Moreover, the mechanism behind string cavitation occurrence is still unclear. String cavitation usually occurs at low needle lift, which might indicate the existence of a vortex ring flow in the sac. However, because of the difficulty in precise flow measurement of the three-dimensional flow structure in the sac, the link between vortex ring flow and string cavitation occurrence in the sac has not been proven. In this study, high-speed imaging of string cavitation, geometrical cavitation, and discharged liquid jet of an enlarged three-hole mini-sac diesel fuel injector was conducted to individually clarify the effects of string cavitation and geometrical cavitation on the discharged liquid jet angle. Furthermore, tomographic–stereo particle image velocimetry was carried out on the sac. The experiments were conducted at two different needle lifts, to clarify the link between needle lifts and flow structure in the sac, as well as how it affects string cavitation occurrence and liquid jet angle. The results confirmed that at low needle lift, vortex ring flow forms in the sac, which may induce helical flow in the nozzle, resulting in a large jet angle. Vortex strength varies with time, and string cavitation occurs when the vortex is particularly strong. As a result, the magnitude of the jet angle increase at low needle lift is enhanced when string cavitation occurs. At high needle lift, flow pattern in the sac becomes relatively uniform, which makes it harder for string cavitation to form.

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The influence of eccentric needle movement on internal flow and injection characteristics of a multi-hole diesel nozzle

Cited by 31 publications

References 37 publications

Visual experimental investigations of string cavitation and residual bubbles in the diesel nozzle and effects on initial spray structures

Visual experimental investigations of string cavitation and residual bubbles in the diesel nozzle and effects on initial spray structures

Effect of the In-Cylinder Back Pressure on the Injection Process and Fuel Flow Characteristics in a Common-Rail Diesel Injector Using GTL Fuel

Three-dimensional flow structure and string cavitation in a fuel injector and their effects on discharged liquid jet

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