IMPORTANCE OF INTERNAL FLOW AND

Transcription

1 IMPORTANCE OF INTERNAL FLOW AND GEOMETRY MODELLING IN THE GM 1.9L LIGHT DUTY ENGINE F. Perini a, P. C. Miles b, R. D. Reitz a a University of Wisconsin-Madison b Sandia National Laboratories ERC Seminar Madison, WI Nov 19, 13 Acknowledgements: This research is funded by the Sandia National Laboratories slide 1 ERC Seminar Madison, WI Nov 19, 13

2 Outline Motivation and challenges Capturing internal flows in the Sandia light-duty optical Diesel engine Code development Engine Geometry representation Adjustable swirl-ratio modelling Fluid flow validation vs. PIV measurements (Preliminary) Capturing the effects of flow, composition and thermal non-uniformities on HCCI combustion slide ERC Seminar Madison, WI Nov 19, 13

3 Local mixture formation Motivation KIVA, -. CA Experiment, -. CA The success of advanced combustion strategies heavily relies 1 on local mixture preparation Engine sector simulations incorporate geometrical - - simplification Global performance and azimuthal averaging An average-of-the-average P1, y axis [cm] P, y axis [cm] -. Extremely accurate at predicting global engine behavior, but can fail when local phenomena are KIVA, relevant Rs = apparent heat release [J/deg] 3 1 AHRR, p inj = 86 bar, R s sweep Exp, Rs = 1. KIVA, Rs =. Exp, Rs =. KIVA, Rs = 3. Exp, Rs = crank angle [degrees ATDC] P3, y axis [cm] x axis [cm] x axis [cm] slide 3 ERC Seminar Madison, WI Nov 19, 13

4 Motivation The success of advanced combustion strategies heavily relies on local mixture preparation Engine sector simulations incorporate geometrical simplification and azimuthal averaging An average-of-the-average Extremely accurate at predicting global engine behavior, but can fail when local phenomena are relevant Can detailed engine modeling improve the simulation s predictiveness and provide a computational counterpart to the extensive set of experimental measurements carried out on this engine? slide ERC Seminar Madison, WI Nov 19, 13

5 Challenges Even with an adaptive meshing methodology and local cell refinements only where needed, the total grid size for a complete engine facility easily adds up to > k cells Code parallelization needed for practical simulations on multi-core computers Solver numerics (Jacobi-preconditioned CR method) are outdated Unmanageably large number of iterations per time step Convergence is not always guaranteed (e.g. at the valve openings) Reaction mechanisms for multiple and multi-component fuels are quickly increasing in size, thanks to advanced chemistry solvers (e.g., SpeedCHEM) The same number of species has to be advected by the fluid flow solver! slide ERC Seminar Madison, WI Nov 19, 13

6 Workflow Build a reliable model for the Sandia-GM 1.9L light-duty Diesel engine to explore advanced combustion concepts RANS approach is optimal for reproducing ensemble-averaged experimental measurements Implementation of state-of-the-art numerics, spray and chemistry models on the remains of the KIVA solver To do so, we need add up to the model the following bricks, in this order: 1. [Geometry] Accurate optical engine geometry. [CFD] Validate fluid flow predictions 3. [Numerics] Accurate, fast reactive flow solvers. [Combustion] Validate vs. HCCI ignition experiments. [Spray] Validate vs. local mixture formation Use the predictive tool to explore further combustion strategies This pres. slide 6 ERC Seminar Madison, WI Nov 19, 13

7 Engine geometry modelling Detailed combustion chamber Improved wall boundary treatment Intake and exhaust runners Pressure vessels 6k cells at BDC 3k cells at TDC slide 7 ERC Seminar Madison, WI Nov 19, 13

8 Engine geometry modelling Detailed combustion chamber Improved wall boundary treatment Refined unstructured mesh - Crevice and near-liner region - Valve seats and stems Intake and exhaust runners Pressure vessels 6k cells at BDC 3k cells at TDC slide 8 ERC Seminar Madison, WI Nov 19, 13

9 Engine geometry modelling Detailed combustion chamber Improved wall boundary treatment Intake and exhaust runners Pressure vessels - Modified KIVA code for multi-layered valves - arbitrary # of cell layers at the intake for discharge coefficient capturing 6k cells at BDC 3k cells at TDC slide 9 ERC Seminar Madison, WI Nov 19, 13

10 Engine geometry modelling Detailed combustion chamber Recesses Chamfered piston bowl shape DERC piston bowl shape Improved wall boundary treatment Intake and exhaust runners Pressure vessels Non-tuned crevice height 6k cells at BDC 3k cells at TDC slide 1 ERC Seminar Madison, WI Nov 19, 13

11 Initial and boundary conditions Exhaust region Composition: measured, exhaust p, T: from transducers Intake region Composition: arbitrary fresh air + measured EGR comp p, T: from intake transducers Injections Actual timing, duration, injected mass and fuel composition from the bench data Cylinder Composition: measured, exhaust p, T: from pressure trace slide 11 ERC Seminar Madison, WI Nov 19, 13

12 Swirl generation modelling Helical Different swirl ratios are obtained by throttling the intake ports Tangential Adjustable throttles are mounted on the intake ports High swirl: Tangential port open, helical port throttled Low swirl: Tangential port throttled (7), helical port throttled (1) T H Modeled using a layer of cells, deactivated and with their faces set as a solid wall slide 1 ERC Seminar Madison, WI Nov 19, 13

13 Intake throttle generation Cells are identified, rotated, accordioned and deactivated From streamwise cells Example T H From cross-sectional layer Tangential pin = 19, Helical pin = Tangential pin = 19, Helical pin = 1 slide 13 ERC Seminar Madison, WI Nov 19, 13

14 Intake throttle generation Cells are identified, rotated, accordioned and deactivated From streamwise cells From cross-sectional layer Example This model is not perfect! - No throttle stem - At least one cell layer per T side - Area opposed to flow is not H exactly the correct one when cross-sectional layer is used Tangential pin = 19, Helical pin = Tangential pin = 19, Helical pin = 1 slide 1 ERC Seminar Madison, WI Nov 19, 13

15 Intake throttle generation Cells are identified, rotated, accordioned and deactivated From streamwise cells From cross-sectional layer Example However! This model is not perfect! - No throttle stem Achieving a more accurate geometry - At least would one cell pose layer significant per T modelling side problems on a hexahedral - Area opposed mesh to flow is not H exactly the correct one when cross-sectional layer is used Tangential pin = 19, Helical pin = Tangential pin = 19, Helical pin = 1 slide 1 ERC Seminar Madison, WI Nov 19, 13

16 Swirl generation modelling Helical port throttling Tangential port throttling 7 max swirl ratio during intake [-] 6 3 UW Production UW single cylinder GM production KIVA helical port throttle angle [deg] max swirl ratio during intake [-] 3 helical = open helical = 1 pin 1 Helical pin = 11 Helical pin = 1 Helical pin = 11 KIVA 11 helical = pin 11 KIVA 1 KIVA tangential port throttle angle [deg] * Measurements from R. Opat, Master Thesis, UW-Madison, 6 Max swirl ratio during intake is the closest configuration to the swirl meter bench slide 16 ERC Seminar Madison, WI Nov 19, 13

17 Swirl generation modelling Helical port throttling Tangential port throttling 7 max swirl ratio during intake [-] 6 3 UW Production UW single cylinder GM production KIVA helical port throttle angle [deg] max swirl ratio during intake [-] 3 helical = open helical = 1 pin 1 Helical pin = 11 Helical pin = 1 Helical pin = 11 KIVA 11 helical = pin 11 KIVA 1 KIVA tangential port throttle angle [deg] * Measurements from R. Opat, Master Thesis, UW-Madison, 6 Max swirl ratio during intake is the closest configuration to the swirl meter bench slide 17 ERC Seminar Madison, WI Nov 19, 13

18 Swirl generation modelling Helical port throttling Tangential port throttling 7 max swirl ratio during intake [-] 6 3 UW Production UW single cylinder GM production KIVA helical port throttle angle [deg] max swirl ratio during intake [-] 3 helical = open helical = 1 pin 1 Helical pin = 11 Helical pin = 1 Helical pin = 11 KIVA 11 helical = pin 11 KIVA 1 KIVA tangential port throttle angle [deg] * Measurements from R. Opat, Master Thesis, UW-Madison, 6 Max swirl ratio during intake is the closest configuration to the swirl meter bench Match deteriorates when the throttle model lacks of resolution: 1) Throttle almost closed ) Throttle angle between and 7 degrees slide 18 ERC Seminar Madison, WI Nov 19, 13

19 Swirl generation modelling Tangential velocities 3mm below fire-deck vs. PIV (Petersen et al, 11) Fully open ( Rs =. ), different crank angles 1 KIVA- 1 SECTOR tangential velocity [m/s] CA = -. CA = -3. CA = -. (marks) experiments from [XYZ] (lines) KIVA, Bessel fit α =. 1 3 radius [cm] from cylinder axis CA = 3 btdc, different swirl ratios tangential velocity [m/s] 1 1 Rs =. Rs = 3. Rs =. (marks) experiments from [] (lines) KIVA, Bessel fit α =. slide radius [cm] from cylinder axis tangential velocity [m/s] tangential velocity [m/s] CA = -. CA = -3. CA = -. (marks) experiments from [XYZ] (lines) KIVA, full mesh 1 3 radius [cm] from cylinder axis ERC Seminar Madison, WI Nov 19, 13 radius [cm] from cylinder axis Rs =. Rs = 3. Rs =. (marks) experiments from [XYZ] (lines) KIVA, full mesh FULL

20 Swirl generation modelling Tangential velocities 3mm below fire-deck vs. PIV (Petersen et al, 11) Fully open ( Rs =. ), different crank angles 1 KIVA- 1 SECTOR tangential velocity [m/s] CA = -. CA = -3. CA = -. (marks) experiments from [XYZ] (lines) KIVA, Bessel fit α =. 1 3 radius [cm] from cylinder axis CA = 3 btdc, different swirl ratios tangential velocity [m/s] 1 1 CA Rs Rs =. Rs = 3. Rs =. (marks) experiments from [] (lines) KIVA, Bessel fit α =. slide 1 3 radius [cm] from cylinder axis tangential velocity [m/s] tangential velocity [m/s] CA = -. CA = -3. CA = -. (marks) experiments from [XYZ] (lines) KIVA, full mesh 1 3 radius [cm] from cylinder axis 1 1 CA Rs 1 3 ERC Seminar Madison, WI Nov 19, 13 radius [cm] from cylinder axis Rs =. Rs = 3. Rs =. (marks) experiments from [XYZ] (lines) KIVA, full mesh FULL

21 Swirl generation modelling Tangential velocities 3mm below fire-deck vs. PIV (Petersen et al, 11) Fully open ( Rs =. ), different crank angles SECTOR tangential velocity [m/s] KIVA- CA = 3 btdc, different swirl ratios tangential velocity [m/s] (marks) experiments from [] (lines) KIVA, Bessel fit α =. slide radius [cm] from cylinder axis tangential velocity [m/s] 6 6 CA = -. CA = -. CA = -3. CA = -3. CA = -. CA = -. Swirl, bench IVC IVC (marks) experiments from [XYZ] (marks) experiments from [XYZ] (lines) KIVA, Bessel fit α =. (lines) KIVA, full mesh Rs = radius [cm] from cylinder axis radius [cm] from cylinder axis 1 1 CA Rs Rs =. Rs =...8 Rs = 3. Rs =. tangential velocity [m/s] CA Rs = Rs 1 3 ERC Seminar Madison, WI Nov 19, 13 radius [cm] from cylinder axis Rs =. Rs = 3. Rs =. (marks) experiments from [XYZ] (lines) KIVA, full mesh FULL

22 Effect of throttling strategy on flow field - Vertical cross sections at the intake valves CA = slide ERC Seminar Madison, WI Nov 19, 13

23 Full vs. sector mesh velocities Rs =. throttles fully open Full mesh * After full induction stroke calculation Sector 1 Smaller in-bowl velocities when having intakegenerated swirl smaller overall momentum than the IVC, Bessel fit imposed swirl profile In the spray jet targeting zone, the high velocity region appears to be set by the valve recesses on the head slide 3 ERC Seminar Madison, WI Nov 19, 13

24 Full vs. sector mesh velocities Rs The = sector. simulations are: throttles fully -Overpredicting open jet deflection in the central part of the cylinder - Underpredicting jet penetration deep into the bowl 1 - Smaller in-bowl velocities when having intakegenerated swirl smaller overall momentum than the IVC, Bessel fit imposed swirl profile P1, y axis [cm] P, y axis [cm] P3, y axis [cm] - - KIVA, -. CA Full mesh Experiment, -. CA * After full induction stroke. calculation Sector - In - the spray jet targeting - zone, the high x axis velocity [cm] region appears x axis [cm] to be set by the valve recesses on the head slide ERC Seminar Madison, WI Nov 19, 13

25 Full vs. sector mesh average flow properties - A significant amount of calibration is needed to match near- TDC velocities with a sector simulation - Imposed momentum conservation - Swirl vortex axisymmetry - Absence of geometric details in-cylinder - Even after calibration, prediction of in-cylinder turbulent kinetic energy and dissipation rate appear drastically underestimated full geometry sector swirl ratio [-] predicted swirl comparison Rs = 1. Rs =. Rs = 3. Rs =. full sector (solid) full mesh, (dashed+marks) sector mesh crank angle [degrees ATDC] turbulent kinetic energy [m /s ] T [m /s ] crank angle [degrees ATDC] slide sector simulation full engine geometry turbulent length scale [mm] L T [mm] sector simulation full engine geometry crank angle [degrees ATDC] turbulent dissipation [m /s 3 ] x ε T [m /s 3 ] sector simulation full engine geometry crank angle [degrees ATDC] ERC Seminar Madison, WI Nov 19, 13

26 Swirl center identification The swirling vortex in the engine shows precession during compression, and vertical tilting radial [cm/s] INTAKE y [mm] EXHAUST Swirl center precession, CA = -, -, - atdc CA CA precession R s =. R s = 3. R s =. (solid) KIVA (dashed) exp x [mm] Vortex identification (Michard et al., 1997) max INTAKE y [mm] EXHAUST Swirl center tilt [3, 1, 18 mm below firedeck] R s =. R s = 3. R s =. (solid) KIVA (dashed) exp tilting x [mm] r 1 { ( )} ( PM vm ) Γ P = max S M Ω PM r v M z zˆ ds Ω - - tangential [cm/s] vertical [cm/s] - - exhaust x [cm] intake -1 1 slide 6 ERC Seminar Madison, WI Nov 19, 13

27 INTAKE y [mm] EXHAUST Swirl center identification The swirling vortex in the engine shows precession during compression, and vertical tilting Swirl center precession, CA = -, -, - atdc CA CA Fully open, Rs =. configuration (blue) precession tilting captures values well, not only trends R s =. R s = 3. R s =. (solid) KIVA (dashed) exp x [mm] Vortex identification (Michard et al., 1997) INTAKE y [mm] EXHAUST Swirl center tilt [3, 1, 18 mm below firedeck] R s =. R s = 3. R s =. (solid) KIVA (dashed) exp Velocities 3mm below firedeck reflect close presence of the valve r 1 { ( )} ( PM vm ) max Γregions P = max x [mm] S M Ω PM r v M z zˆ ds Ω - - radial [cm/s] tangential [cm/s] vertical [cm/s] - - exhaust x [cm] intake -1 1 slide 7 ERC Seminar Madison, WI Nov 19, 13

28 In-cylinder temperature stratification Rs =., IVC INTAKE EXHAUST Cross section Temperature stratification is significant (> 3K) at IVC highest temperatures within the bowl, clue to less efficient removal of the exhaust gases Rs =., TDC Cross section! Crucial for HCCI combustion and reaction mechanism validation Some temperature stratification ( 1K) survives within the bowl even until the end of the compression stroke may be greater at lower swirl ratios slide 8 ERC Seminar Madison, WI Nov 19, 13

29 On-going work Tangential port Bosch CRIP. 1) HCCI operation is achieved through dual port fuel injection A common-rail injector injects small amounts of n-heptane at low pressure A PFI injector injects iso-octane Helical port TFS 89-1 Complete full-cycle HCCI simulations with comprehensive flow, fuel injection, and combustion modelling ) KIVA solver improvement and parallelization - Mesh movement with automatic re-partitioning using METIS - Replacement of the CR solver with a specific accurate and fast solver for simulations with many species slide 9 ERC Seminar Madison, WI Nov 19, 13

30 Conclusions The comprehensive engine model captures intake flows reasonably well Significant cold flow deviations are observed when comparing the full model with the sector mesh representation Development of advanced numerics is preparing the path towards real-world full engine simulations with detailed chemistry and spray Future work Understand the effects of detailed geometry and flow non-uniformities (temperature and composition too!) on HCCI Help to quantify initialization uncertainties in sector mesh simulations Capture the effects of detailed geometry on spray jet-by-jet discrepancies and local mixture preparation slide 3 ERC Seminar Madison, WI Nov 19, 13

31 Thanks for your attention! Questions? Acknowledgements U.S. D.O.E., Sandia National Laboratories Paul C. Miles, Rolf D. Reitz Dipankar Sahoo equivalence ratio measurements Adam B. Dempsey, N. Ryan Walker model development and experiments on the DERC engine slide 31 ERC Seminar Madison, WI Nov 19, 13 Randy Hessel, Joshua Leach computing infrastructure access and setup