Prediction And Design Of Fuel-Air Mixing in a Combustion Wave Rotor Using Two-Dimensional Unsteady Moving Mesh Flow Comp

1. Prediction And Design Of Fuel-Air Mixing in a Combustion Wave Rotor Using Two-Dimensional Unsteady Moving Mesh�Flow Computation Arnab Banerjee Mechanical Engineering IUPUI MSME Thesis Presentation Advisor: Prof. Razi Nalim November 27, 2005

2. Objectives of the present work Develop a methodology to study multidimensional effects of wave rotors and apply to NASA four-port pressure exchanger using commercial CFD code Predict the fuel-air mixing in an internal combustion wave rotor (ICWR) Determine key parameters that affect the fuel-air distribution in a wave rotor and improve understanding to obtain desired fuel distribution

3. Introduction Wave Rotor: A device for energy exchange efficiently within fluids of differing densities by utilizing unsteady wave motion Two configurations studied here NASA four-port pressure exchanger Internal combustion wave rotor (ICWR)

4. NASA four-port pressure exchanger Turbine inlet pressure is 15% -20% more than compressor exit pressure ideally Increased overall engine thermal efficiency and specific work

5. Internal Combustion Wave Rotor (ICWR)

6. 2D & 3D view of wave rotor

7. Pre- and Post- Processing Package Developed in-house by Khalid (2004-05) Hexagonal unstructured grid Parametric geometry and grid Grid and geometry stored in small portable files Variable port/rotor channel counts and shape Tailored grid clustering Imports and exports STAR-CD files 3D and �unwrapped� simultaneous view Runs easily on laptops (windows)

8. Results of two grid packages

9. Past 1-D simulations

10. Past 2-D simulations

11. Solution Methodology Arbitrary Sliding Interface MARS (Monotone Advection Reconstruction Scheme) � 2nd order accurate PISO predictor-corrector algorithm Corrector stages below specified limit (20) indicates convergence reached for specified residual tolerance

12. Arbitrary Sliding Interface

13. Estimating Artificial Diffusivity Use shock tube with different grid resolutions representing the range of CFD simulations carried out Calculated artificial diffusion from known equation Compared these values with physical diffusivity in simulations

15. Hardware Resources AVIDD Linux Cluster Huge Scratch space Batch Scheduling Accessible from outside of network (SSH) Dual CPU PC Quick turnaround Debugging Manual decomposition

16. Methodology Development Welch (1997) simulated NASA 4-port configuration using code validated against experiment 2D unsteady, laminar, compressible, ideal gas, adiabatic walls, no leakage IUPUI simulation Same as above and also included passage to passage leakage

17. Grid Resolution

19. Computed instantaneous total temperature

21. Computed instantaneous static temperature contours showing close up view of passage gradual opening process and 2D flow features

22. Fuel-Air Mixing in an Internal Combustion Wave Rotor (ICWR) Include multidimensional effects Include turbulence modeling (k-epsilon with wall functions) Include species transport equations Include property dependence on mixture composition and temperature Examine the effect of fuel-air distribution on combustion

23. Boundary Conditions - from Alparslan, Nalim and Synder (2004) Inlet was specified as total conditions Total pressure at inlet segments ? 109 KPa Total temperature at inlet segments ? 291 K Exit port was specified as static conditions Static pressure at ? 72 KPa Hot gas injection port Static temperature ? 600 K Combustion using one-step reaction combined time scale model C3H8 + 5O2 ? 3CO2 + 4H2O the reaction time scale is the sum of the dissipation and chemical kinetics time scales.

24. ICWR geometry

25. Grid Resolution

27. Non-Combustion Pressure waves for time converged solution

29. Shape of fuel-air interface Fuel-air interface at the middle of the inlet has expected skew (tangential non-uniformity) due to passage opening to fuel over time Fuel-air interface forming at the beginning of the inlet is less skew The skew of interface maybe something useful to control

30. Close-up view of first inlet segment opening to rotor passage�tufts indicate flow vectors relative to rotor�

31. Developing more uniform fuel-air interface All the inlet port segments have the same total pressures First inlet segment has higher static pressure than other segments due to higher pressure from rotor passage Thus absolute velocity in the first inlet segment is lower than other segments Non-axial relative velocity forces more fuel into the trailing side of the passage

32. Reduced total pressure at first inlet segment

33. Increased total pressure at first inlet segment

34. Results of varying total pressure at first inlet segment Decreasing total pressure at first inlet segment has backflow ? not helping in the fuel distribution shape in other passages The fuel-air interface is skewed similar to fuel air interaction in middle of inlet ports Increasing total pressure at first inlet segment causes no backflow The fuel-air interface is skewed too

35. Adding air-buffer as first inlet segment

36. Results from air buffer case The non-axial relative velocity in the first inlet segment which doesn�t have fuel ? doesn�t influence the filling of fuel in passage The fuel-air surface is skewed similar to the fuel-air surface in the middle of the inlet port

38. Setup - combustion case Boundary conditions obtained from 1-D detonation model. The present case is studied for deflagration and 2-D ? incompatible with 1-D BCs Modified BCs to velocity ? high flow causing choke exhaust Used case to study general effect of fuel-air distribution on combustion

41. Results of combustion case Premature ignition when fuel-air mixture from first three inlet segments due to hot products from previous cycle Presence of air buffer as first inlet segment prevents premature combustion

42. Skewness (tangential non-uniformity)

43. Comparison of penetration of fuel for both configurations

44. Conclusions Developed methodology for 2-D wave rotor simulation Compared with published 2-D simulation results by Welch (1997) Used commercial solver for CFD simulations Applied methodology to ICWR Studied multidimensional factors affecting fuel-air distribution on few configurations With no air buffer � skew can be affected by timing, total inlet conditions Premature ignition can be prevented by air-buffer To do a higher fidelity simulation, of a given wave rotor configuration, include a finer grid based on NASA 4-port wave rotor and geometry and boundary conditions obtained from one-dimensional deflagration.