Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

1. Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines Gregory M. Shaver Dynamic Design Lab May 6th, 2005 Department of Mechanical Engineering Stanford University

2. Outline • What is residual-affected HCCI? What are its benefits? • Hurdles to practically implementing HCCI • Lack of combustion trigger • Cyclic coupling • Dynamic modeling of HCCI • Making HCCI practical with feedback control • Conclusions and future work Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

3. What is Residual-Affected HCCI? • Residual-Affected Homogeneous Charge Compression Ignition • Advanced combustion strategy for piston engines • Combustion due to uniform auto-ignition using compression alone • Hot exhaust gases reinducted using Variable Valve Actuation (VVA) • Main benefits • Increased efficiency compared to SI • Modest compression ratios • Drastic reduction in NOx emissions (i.e. smog) Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

4. HCCI with Variable Valve Actuation Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

5. HCCI with Variable Valve Actuation • Reactants (fuel & air) & previously exhausted gases (residual) inducted Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

6. HCCI with Variable Valve Actuation • Reactants (fuel & air) & previously exhausted gases (residual) inducted • Compression of mixture Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

7. HCCI with Variable Valve Actuation • Reactants (fuel & air) & previously exhausted gases (residual) inducted • Compression of mixture causes auto-ignition • uniform, fast & uncontrolled Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

8. HCCI with Variable Valve Actuation • Reactants (fuel & air) & previously exhausted gases (residual) inducted • Compression of mixture causes auto-ignition • uniform, fast & uncontrolled • Useful work from expansion Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

9. HCCI with Variable Valve Actuation • Reactants (fuel & air) & previously exhausted gases (residual) inducted • Compression of mixture causes auto-ignition • uniform, fast & uncontrolled • Useful work from expansion • Hot combustion products exhausted Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

10. HCCI with Variable Valve Actuation • Reactants (fuel & air) & previously exhausted gases (residual) inducted • Compression of mixture causes auto-ignition • uniform, fast & uncontrolled • Useful work from expansion • Hot combustion products exhausted, portion reinducted Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

11. HCCI with Variable Valve Actuation • Valve motions from VVA determine: • inducted gas composition • amount of compression Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

12. HCCI with Variable Valve Actuation Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

13. HCCI with Variable Valve Actuation • Sudden rise in pressure combustion initiation Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

14. HCCI with Variable Valve Actuation • Sudden rise in pressure combustion initiation • Work output: Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

15. HCCI with VVA -Challenges • Goal: achieve desired combustion timing & work output • Challenges • No direct initiator of combustion • Cycle-to-cycle coupling through exhaust gas • Significantly complicate transient load operation Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

16. HCCI with VVA -Challenges • Goal: achieve desired combustion timing & work output • Challenges • No direct initiator of combustion • Cycle-to-cycle coupling through exhaust gas • Significantly complicate transient load operation • To date – HCCI impractical!! Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

17. Research Goals • Make HCCI practical through closed-loop control • Stabilize process & control work output • Modeling Objective: Simple physical models that capture behavior most relevant for control • Cyclic coupling • Combustion timing • In-cylinder pressure evolution (work output) • Control Objective - Control of: • Combustion timing – make combustion sure happens! • Work output – the key output of the engine • efficiency & reduced emissions come as result of process Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

18. Previous Work – Simulation Modeling • Ogink and Golovitchev 2002, Babajimopoulos et al. 2002 • Multi-zone modeling of HCCI • Kong et al. 2002 • Multi-dimensional CFD models using detailed chemistry • Many others Complex flow and chemical kinetics models • Capture general steady state behavior • Ignore cycle-to-cycle coupling • Exhibit long run times - ~12 hours per engine cycle Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

19. Contributions – Simulation Modeling • Developed a simulation model of residual-affected HCCI that: • Captures the cyclic coupling • Predicts behavior during steady state & transients • Captures ignition via kinetics with a simple, intuitive model • runtimes: ~ 15 seconds per engine cycle (amenable to use as a control testbed) Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

20. Previous Work - Control • Agrell et al. 2003, Haraldsson et al. 2003, Bengtsson et al. 2004, Olsson et al. 2001, Matthews et al. 2005, others • Various approaches to control combustion timing or work output • In all cases: controller hand-tuned or synthesized from black-box models Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

21. Contributions - Control • Physics-based control model of HCCI • The first physics-based approach to control of HCCI • Generalizable • Enables use of control engineering tools: • Theoretical control design • Stability analysis • Control strategies for: • Combustion timing • Peak pressure or work output Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

22. Outline - Modeling Strategies • Simulation model • Gain some intuition of the process • What are key features? • What are relevant control inputs & outputs? • Control model • Need a slightly simpler physical description for synthesis • The launching point for developing control strategies …..making HCCI practical!! Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

23. Experimental Apparatus • Single cylinder engine • With VVA • Fuel used: Propane • Compression ratio • Variable: 13-15.5 • Engine speed • Fixed: 1800 rpm • In-cylinder pressure transducer • Combustion timing • Peak pressure • Work output Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

24. HCCI Simulation Model • 1st law analysis of cylinder and exhaust manifold Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

25. HCCI Simulation Model • 1st law analysis of cylinder and exhaust manifold • Steady state 1D compressible flow relations Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

26. HCCI Simulation Model • 1st law analysis of cylinder and exhaust manifold • Steady state 1D compressible flow relations • Heat transfer • In-cylinder (modified Woschni) • Ref: Chang et al. 2004 • Exhaust manifold Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

27. HCCI Simulation Model • 1st law analysis of cylinder and exhaust manifold • Steady state 1D compressible flow relations • Heat transfer • In-cylinder (modified Woschni) • Ref: Chang et al. 2004 • Exhaust manifold • Combustion model • Wiebe function • What do we use as a combustion trigger? Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

28. HCCI Simulation Model • 1st law analysis of cylinder and exhaust manifold • Steady state 1D compressible flow relations • Heat transfer • In-cylinder (modified Woschni) • Ref: Chang et al. 2004 • Exhaust manifold • Combustion model • Wiebe function • What do we use as a combustion trigger? Resulting Model – 9 nonlinear ODEs Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

29. Temperature Threshold • Assume HCCI occurs at a threshold temperature • A fit at one temperature… Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

30. Temperature Threshold • Assume HCCI occurs at a threshold temperature • Fit at one temperature… doesn’t hold at others! Increasing residual Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

31. What Happened? • Simulation model: earlier timing for increasing residual • More residual means mixture temperature • Higher temperature leads to early timing • Experiments show more constant timing • Is some physical effect missing? • Yes! Concentration of reactants • More residual means lower reactant concentration Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

32. Integrated Arrhenius Rate Equation • Simple model for start of combustion • Integrated Arrhenius rate • Constant threshold, • a, b and Ea from published experiments • Contributions from temperature & reactant concentration captured Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

33. Integrated Arrhenius Rate • Set threshold at one operating point… Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

34. Integrated Arrhenius Rate • Set threshold at one operating point… …and pressure, timing & work output at all points is captured Increasing residual Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

35. Integrated Arrhenius Rate • Note: can vary composition without much change in timing Increasing residual Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

36. Simulation Model: Can it be extended? • Steady state behavior with propane captured • What about transients? • Changes in load • Can the model capture these? Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

37. Simulation Model: Transients • 1st operating point has higher steady state temperature than 2nd • The elevated exhaust temperature advances combustion process during transition • As exhaust temperature decreases, behavior reaches new steady state Experiment Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

38. Simulation Model: Transients Experiment • Simple model captures the coupling and ignition behavior during transition Simulation Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

39. Results from Simulation modeling • Aspects most relevant for control captured with simple simulation model: • Cyclic coupling & combustion timing • In-cylinder pressure evolution • Approach can handle: • Steady-state behavior • Transients • A valuable virtual testbed for control Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

40. Motivation for Control Model • Simulation model has a lot of benefits • Still, too complex for synthesizing control strategies • Motivates a simpler dynamic model • Enabled through additional physical assumptions • Discretizing the process (induction, compression, etc.) • Linking processes Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

41. Control Model Assumptions • Assumptions: • Induction: atmospheric pressure • Isentropic compression & expansion • HCCI is fast: constant volume combustion • In-cylinder heat transfer:% of combustion energy Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

42. Control Model Assumptions Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

43. A Simple Control Model Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

44. A Simple Control Model • Step through process to develop model of dynamics Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

45. A Simple Control Model • Step through process to develop model of dynamics dynamics Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

46. Peak Pressure Dynamics • The peak pressure dynamics takes the form: • Fairly complex nonlinear dynamic model Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

47. Peak Pressure Dynamics • The peak pressure dynamics takes the form: • Fairly complex nonlinear dynamic model • Can see dependence on: • Control inputs Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

48. Peak Pressure Dynamics • The peak pressure dynamics takes the form: • Fairly complex nonlinear dynamic model • Can see dependence on: • Control inputs • Cyclic coupling Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

49. Peak Pressure Dynamics • The peak pressure dynamics takes the form: • Fairly complex nonlinear dynamic model • Can see dependence on: • Control inputs • Cyclic coupling • Combustion timing Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines

50. Peak Pressure Dynamics • The peak pressure dynamics takes the form: • Fairly complex nonlinear dynamic model • Can see dependence on: • Control inputs • Cyclic coupling • Combustion timing • How do we model initiation of combustion, qcomb? Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines