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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Predictions of Transient Flame Lift-off Length With Comparison to Single-Cylinder Optical Engine Experiments

[+] Author and Article Information
P. K. Senecal

Convergent Science, Inc.,
Middleton, WI 53562
e-mail: senecal@convergecfd.com

E. Pomraning

Convergent Science, Inc.,
Middleton, WI 53562
e-mail: pomraning@convergecfd.com

J. W. Anders

Caterpillar, Inc.,
Peoria, IL 61629
e-mail: anders_jon@cat.com

M. R. Weber

Caterpillar, Inc.,
Peoria, IL 61629
e-mail: weber_marcus_r@cat.com

C. R. Gehrke

Caterpillar, Inc.,
Peoria, IL 61629
e-mail: gehrke_christopher_r@cat.com

C. J. Polonowski

Sandia National Laboratories,
Livermore, CA 94551
e-mail: cpolonow@ford.com

C. J. Mueller

Sandia National Laboratories,
Livermore, CA 94551
e-mail: cjmuell@sandia.gov

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received March 4, 2014; final manuscript received April 28, 2014; published online May 28, 2014. Editor: David Wisler. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

J. Eng. Gas Turbines Power 136(11), 111505 (May 28, 2014) (19 pages) Paper No: GTP-14-1138; doi: 10.1115/1.4027653 History: Received March 04, 2014; Revised April 28, 2014

A state-of-the-art, grid-convergent simulation methodology was applied to three-dimensional calculations of a single-cylinder optical engine. A mesh resolution study on a sector-based version of the engine geometry further verified the RANS-based cell size recommendations previously presented by Senecal et al. (“Grid Convergent Spray Models for Internal Combustion Engine CFD Simulations,” ASME Paper No. ICEF2012-92043). Convergence of cylinder pressure, flame lift-off length, and emissions was achieved for an adaptive mesh refinement cell size of 0.35 mm. Full geometry simulations, using mesh settings derived from the grid convergence study, resulted in excellent agreement with measurements of cylinder pressure, heat release rate, and NOx emissions. On the other hand, the full geometry simulations indicated that the flame lift-off length is not converged at 0.35 mm for jets not aligned with the computational mesh. Further simulations suggested that the flame lift-off lengths for both the nonaligned and aligned jets appear to be converged at 0.175 mm. With this increased mesh resolution, both the trends and magnitudes in flame lift-off length were well predicted with the current simulation methodology. Good agreement between the overall predicted flame behavior and the available chemiluminescence measurements was also achieved. The present study indicates that cell size requirements for accurate prediction of full geometry flame lift-off lengths may be stricter than those for global combustion behavior. This may be important when accurate soot predictions are required.

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

Cross-sectional view of the optical engine showing how in-cylinder processes are imaged through the piston window

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Fig. 2

Measured cylinder pressure during a portion of the engine cycle for the five SOC cases

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Fig. 3

Intake and exhaust valve lift profiles for the optical research engine

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Fig. 4

Computational geometry showing the cylinder, ports, and runners (left) and the piston bowl (right)

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Fig. 5

Injection velocity as a function of crank angle for the optical engine simulations. Note that the start of injection is shifted appropriately depending on the case.

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Fig. 6.

Definition of the cut-plane (red line) used to visualize the computational mesh and velocity fields for the gas-exchange simulation

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Fig. 7

Computational mesh at −410 deg ATDC (left) and −310 deg ATDC (right), illustrating the fixed embedding and AMR strategies

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Fig. 8

Velocity magnitude in the cut-plane defined in Fig. 6 at (a) −350, (b) −310, (c) −270, (d) −230, (e) −190, and (f) −150 deg ATDC

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Fig. 9

Predicted swirl and tumble levels during the gas-exchange process

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Fig. 10

Cell count histories for the six mesh resolutions investigated for the 4SOC, sector geometry case

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Fig. 11.

Zoomed-out (a) and zoomed-in (b) cylinder pressure comparisons for the six mesh resolutions investigated for the 4SOC, sector geometry case

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Fig. 12

Predicted soot (a) and NO (b) for the six mesh resolutions investigated for the 4SOC, sector geometry case

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Fig. 13

OH mass fraction on a cut-plane through the center of the spray for the six mesh resolutions investigated for the 4SOC, sector geometry case at 15 deg ATDC

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Fig. 14

Comparison of the predicted flame lift-off length for the six mesh resolutions investigated with the measured value for the 4SOC, sector geometry case at 15 deg ATDC

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Fig. 15

Comparison of the measured and predicted (sector geometry) average cylinder pressure for the (a) −2SOC, (b) OSOC, (c) 2SOC, (d) 4SOC, and (e) 6SOC cases. The predictions are for a cell size of 0.35 mm and a cell count limit of 300,000 cells.

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Fig. 16

Comparison of the measured and predicted (sector geometry) flame lift-off lengths at 15 deg ATDC for the five start-of-combustion cases. The predictions are for a cell size of 0.35 mm and a cell count limit of 300,000 cells.

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Fig. 17

Comparison of the predicted (sector geometry) flame locations at 15 deg ATDC for the (a) −2SOC, (b) OSOC, (c) 2SOC, (d) 4SOC, and (e) 6SOC cases. The predictions are for a cell size of 0.35 mm and a cell count limit of 300,000 cells.

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Fig. 18

Comparison of the measured and predicted (full geometry) average cylinder pressure (left) and heat release rate (right) for the (a) −2SOC, (b) OSOC, (c) 2SOC, (d) 4SOC, and (e) 6SOC cases. The predictions are for a cell size of 0.35 mm and a cell count limit of 2 × 106 cells.

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Fig. 19

Comparison of the measured and predicted (full geometry) NOx emissions as a function of start-of-combustion timing. The predictions are for a cell size of 0.35 mm and a cell count limit of 2 × 106 cells.

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Fig. 20

Illustration of the jet numbering and OH isosurface used to calculate flame lift-off lengths. The liquid fuel drops are also shown in red.

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Fig. 21

Comparison of the measured and predicted flame lift-off lengths for the five start-of-combustion timings. The predictions on the left-hand side are averages of the six fuel jet lift-off lengths. The predictions on the right-hand side are for jet 4 only.

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Fig. 22

Comparison of the measured and predicted (jets 1 and 4) flame lift-off lengths for the 0SOC case at two different mesh resolutions

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Fig. 23

Comparison of the measured and predicted flame lift-off lengths for the 0SOC case for the (a) 0.35-mm cells and (b) 0.175-mm cells. Both the individual jet lift-off length predictions and their averages are shown.

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Fig. 24

Comparison of the measured and predicted flame lift-off lengths (full geometry) using the 0.175-mm cells for the (a) −2SOC, (b) 0SOC, (c) 2SOC, (d) 4SOC, and (e) 6SOC cases. Both the individual jet lift-off length predictions and their averages are shown.

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Fig. 25

Comparison of the measured and predicted transient flame lift-off lengths for the five start-of-combustion timings for the full geometry, 0.175-mm cell size cases

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Fig. 26

Measured natural luminosity of combusting fuel. This viewing perspective is used later for a comparison of measured and predicted flame locations.

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Fig. 27

Illustration of the technique used to compare the measured and predicted flame locations

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Fig. 28

Comparison of the averaged chemiluminescence experimental images with simulation results for the −2SOC case. The red outline shows the predicted OH location.

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Fig. 29

Comparison of the averaged chemiluminescence experimental images with simulation results for the 0SOC case. The red outline shows the predicted OH location.

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Fig. 30

Comparison of the averaged chemiluminescence experimental images with simulation results for the 2SOC case. The red outline shows the predicted OH location.

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Fig. 31

Comparison of the averaged chemiluminescence experimental images with simulation results for the 4SOC case. The red outline shows the predicted OH location.

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Fig. 32

Comparison of the averaged chemiluminescence experimental images with simulation results for the 6SOC case. The red outline shows the predicted OH location.

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