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Research Papers: Flows in Complex Systems

Characterization of Flow Structures in a Diesel Injector for Different Needle Lifts and a Fluctuating Injection Pressure

[+] Author and Article Information
Alexandre Pelletingeas

TFT Laboratory,
Department of Mechanical Engineering,
École de Technologie Supérieure,
Montréal, QC H3C 1K3, Canada

Louis Dufresne

Professor
TFT Laboratory,
Department of Mechanical Engineering,
École de Technologie Supérieure,
Montréal, QC H3C 1K3, Canada

Patrice Seers

Professor
TFT Laboratory,
Department of Mechanical Engineering,
École de Technologie Supérieure,
Montréal, QC H3C 1K3, Canada
e-mail: patrice.seers@etsmtl.ca

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 11, 2015; final manuscript received March 7, 2016; published online May 19, 2016. Assoc. Editor: John Abraham.

J. Fluids Eng 138(8), 081105 (May 19, 2016) (11 pages) Paper No: FE-15-1552; doi: 10.1115/1.4033125 History: Received August 11, 2015; Revised March 07, 2016

This paper aims at analyzing the needle lift's influence on the internal flow of single-hole diesel injector to identify flow structures. A numerical Reynolds-Averaged Navier–Stokes (RANS) model of a single-hole diesel injector was developed and validated to study the flow's dynamic for different needle's lifts and subjected to realistic injection pressure. The main findings are: (1) under steady injection pressure, flow coefficients reached a steady-state value and maximum injected fuel mass flow rate is reached at intermediate needle's lifts. (2) The sac volume is the area with several vortex structures due to the throttling between the needle body and the injector body. (3) The frequency of the fluctuating injection pressure can excite the initial jet entering the sac volume similarly to the Coanda effect. Finally, using a proper orthogonal decomposition (POD) allowed extracting coherent structures within the sac volume and putting in evidence a reorganization of the flow.

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References

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Figures

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Fig. 1

Injector nozzle design. Adapted from Ref. [17].

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Fig. 2

(a) Overall injector geometry 45 deg, (b) reduced geometry with boundary conditions, and (c) close-up on the sac volume

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Fig. 7

Convergence of the Rp index (top) and of the cumulative energy (bottom) as a function of POD mode and sample size—signal S1—f = 20 kHz

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Fig. 8

Convergence of the Rp index (top) and of the cumulative energy (bottom) as a function of POD mode and sample size—signal S2—f = 1 kHz

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Fig. 6

Reynolds number of the jet at throttling versus dimensionless needle lift for a ΔP = 72 MPa

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Fig. 5

Equivalent solid body rotation (rad/s) in the sac volume as a function of needle lifts for a ΔP = 72 MPa: (a) H* = 0.010, (b) H* = 0.021, (c) H* = 0.042, (d) H* = 0.062—first vortex, (e) H* = 0.062—second vortex, (f) H* = 0.83, (g) H* = 0.10, (h) H* = 0.16, (i) H* = 0.21, and (j) H* = 0.31

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Fig. 4

Velocity field (m/s) in the sac volume as a function of needle lifts for a ΔP = 72 MPa: (a) H* = 0.010, (b) H* = 0.021, (c) H* = 0.042, (d) H* = 0.062, (e) H* = 0.083, (f) H* = 0.10, (g) H* = 0.16, (h) H* = 0.21, (i) H* = 0.31, (j) H* = 0.67, and (k) H* = 1.0

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Fig. 3

Discharge coefficient (Cd) (top), area coefficient (Ca) (middle), and velocity coefficient (Cv) (bottom) as a function of dimensionless needle lift (H*)—ΔP = 72 MPa (dashed line: experimental results of Ref. [17] at H* = 1)

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Fig. 9

Velocity module (m/s) as a function of time H* = 6.2%—signal S1 (f = 20 kHz): (a) t = 0 s, (b) t = 0.025 ms, (c) t = 0.050 ms, (d) t = 0.075 ms, and (e) t = 0.1 ms

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Fig. 10

Evolution of the discharge coefficient (Cd), velocity coefficient (Cv), and area coefficient (Ca) (top), and the dimensionless mass flow rate (bottom) as a function of time H* = 6.2%—signal S1 (f = 20 kHz)

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Fig. 11

Projected velocity (m/s) based on the POD post-treatment of the first (top) and the second (bottom) coherent structure H* = 6.2%—signal S1 (f = 20 kHz)

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Fig. 12

Velocity module (m/s) as a function of time H* = 6.2%—signal S2 (f = 1 kHz): (a) t = 0 s, (b) t = 0.25 ms, (c) t = 0.34 ms, (d) t = 0.36 ms, (e) t = 0.38 ms, (f) t = 0.40 ms, (g) t = 0.50 ms, (h) t = 0.75 ms, and (i) t = 1 ms

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Fig. 13

Equivalent solid body rotation (rad/s) at the beginning (first vortex (top-left) and second vortex (top-right)) and end (bottom) of the pressure oscillation H* = 6.2%—signal S2 (f = 1 kHz): (a) t = 0 s—first vortex, (b) t = 0 s—second vortex, and (c) t = 1 ms

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Fig. 14

Evolution of the discharge coefficient (Cd), velocity coefficient (Cv), and area coefficient (Ca) as a function of time H* = 6.2%—signal S2 (f = 1 kHz)

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Fig. 15

Evolution of the dimensionless turbulent kinetic energy associated to the first three structures as a function of time H* = 6.2%—signal S2 (f = 1 kHz)

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Fig. 16

Projected velocity (m/s) based on POD post-treatment of the first coherent structure (top), the second coherent structure (bottom-left), and the third coherent structure (bottom-right) H* = 6.2%—signal S2 (f = 1 kHz)

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Fig. 17

Amplitude of temporal coefficient ak(t) of the first turbulent structure (top), the second turbulent structure (bottom-left), and the third turbulent structure (bottom-right)H* = 6.2%—signal S2 (f = 1 kHz)

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