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

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 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

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Dynamic Design Lab.Stanford University 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 1. Increased efficiency compared to SI 2. Modest compression ratios 3. Drastic reduction in NO x emissions (i.e. smog)

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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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

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

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Dynamic Design Lab.Stanford University 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:

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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!!

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 18 Previous Work – Simulation Modeling Ogink and Golovitchev 2002, Babajimopoulos et al Multi-zone modeling of HCCI Kong et al 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

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Dynamic Design Lab.Stanford University 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)

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Dynamic Design Lab.Stanford University 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 Various approaches to control combustion timing or work output In all cases: controller hand-tuned or synthesized from black-box models

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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!!

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Dynamic Design Lab.Stanford University 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: Engine speed Fixed: 1800 rpm In-cylinder pressure transducer Combustion timing Peak pressure Work output

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines st law analysis of cylinder and exhaust manifold HCCI Simulation Model

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

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

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

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

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Dynamic Design Lab.Stanford University 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…

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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 E a from published experiments Contributions from temperature & reactant concentration captured

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

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

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Dynamic Design Lab.Stanford University 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

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

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

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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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 1. Enabled through additional physical assumptions 2. Discretizing the process (induction, compression, etc.) 3. Linking processes

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 42 Control Model Assumptions

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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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

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Dynamic Design Lab.Stanford University 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, comb

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 51 Combustion Timing Dynamics Recall the integrated Arrhenius rate model:

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 52 Combustion Timing Dynamics Recall the integrated Arrhenius rate model: Integrand takes on largest value at TDC

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 53 Combustion Timing Dynamics Recall the integrated Arrhenius rate model: Integrand takes on largest value at TDC Simplify: begin integration at TDC with values at TDC

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 54 Combustion Timing Dynamics Recall the integrated Arrhenius rate model: Integrand takes on largest value at TDC Simplify: begin integration at TDC with values at TDC

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 55 Combustion Timing Dynamics Recall the integrated Arrhenius rate model: Integrand takes on largest value at TDC Simplify: begin integration at TDC with values at TDC

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 56 Combustion Timing Dynamics Recall the integrated Arrhenius rate model: Integrand takes on largest value at TDC Simplify: begin integration at TDC with values at TDC Algebraic expression exists for each variable

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 57 Combustion Timing Dynamics Recall the integrated Arrhenius rate model: Integrand takes on largest value at TDC Simplify: begin integration at TDC with values at TDC Algebraic expression exists for each variable

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 58 Control Model Peak pressure and combustion timing dynamics together give: A nonlinear 2-state, dynamic, discrete system model

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 59 Control Model Validation Control model captures Steady state & transient Peak pressure Combustion Timing Captures Cyclic coupling Ignition via kinetics

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 60 Control Modeling Summary HCCI is difficult to control: Cyclic coupling No direct combustion trigger Control model captures these phenomena!! Simple model tells us how dynamics are affected by control inputs Is a launching point for: Synthesizing control strategies Assessing system stability Generalizable

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 61 Outline of Control Implementations From control model 1. Peak-pressure control at constant combustion timing 2. Work output control at constant combustion timing 3. Simultaneous peak pressure and combustion timing control Many other approaches possible

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 62 Peak Pressure Control w/ Constant timing Fix final valve closure Vary composition to control peak pressure A “static” approach to controlling timing A large number of control approaches can be utilized

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 63 Peak Pressure Control w/ Constant timing Linear Controller Synthesis A common control approach is to linearize the system model Linearizing about an operating point yields: Simple linear control laws can be synthesized where:

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 64 Peak Pressure Control w/ Constant timing In closed-loop: Controller synthesized from linearized version of model Is controller stable in closed-loop with nonlinear model?

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 65 Peak Pressure Control w/ Constant timing Nonlinear Stability Analysis Using: Lyapunov stability theory Convex optimization Shows: Simple linear controller stabilizes entire operating regime

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 66 Peak Pressure Control w/ Constant timing Experimental Implementation Accurate control of peak pressure Mean tracking Fluctuation reduction Increases robustness Little change in phase What about direct control of work output (IMEP)?

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 67 Experimental Work Output Control Rapid mean tracking & fluctuation reduction We can control work output, while keeping timing roughly constant

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 68 Experimental Work Output Control Positive and negative load transients What about simultaneous control of combustion timing and work output?

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 69 Combustion Timing & Work Output Control Add other control input: final valve closure Significant control knob for combustion timing Simple approach Separate linear controllers for peak pressure and timing

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 70 Decoupled Peak Pressure and Phase Control Maintain cycle-to-cycle peak pressure controller, vary phase more slowly

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 71 Approach works Simultaneous control of timing and peak pressure Experiments with Decoupled Control

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 72 Comments on Control Experiments Simple physics-based controllers works well Implementation is straightforward Mean tracking & fluctuation reduction of peak pressure work output Combustion timing fairly constant Independent control of peak pressure & combustion timing Many others possible

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 73 Conclusion HCCI has a promising future as a cleaner, more efficient strategy Hurdle: controlling the process No combustion initiator & cycle-to-cycle coupling The good news: HCCI is amenable to model-based control Key behaviors captured in both simulation and control models Simulation & control models capture: Steady-state Transients Physics-based control of: Peak pressure Work output Combustion timing

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 74 Future Work Study different control approaches Control of multi-cylinder HCCI engines Results to date with single-cylinder engines Cylinder-to-cylinder dynamics now play a key role! Change the world!

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Dynamic Design Lab.Stanford University Physics-based Modeling and Control of Homogeneous Charge Compression Ignition (HCCI) Engines - 75 Acknowledgments Chris Gerdes The Dynamic Design Lab Partners in crime: Matt Roelle & Nikhil Ravi A great sponsor – Robert Bosch Corporation Jean-Pierre Hathout, Jasim Ahmed, Aleks Kojic & Sungbae Park The defense Committee Chris Edwards, Sanjay Lall, Matt Franchek & Steve Rock Stanford University

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