AGENDA Engine Population and Background The Opportunity Overview of Air/Fuel Ratio Tech Using Single point injection systems Potential Barriers and So

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Dustin Bell
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gines Fitted with NSCR Systems John Charles Vronay, P.E.

1 Challenges Facing Developers of Air/Fuel Ratio Control Systems for High Speed, Spark-Ignited, Stationary Reciprocating Engines Fitted with NSCR Systems John Charles Vronay, P.E. Consultant Continental Controls Corporation San Diego, California California Energy Commission 4th Annual Advanced Stationary Reciprocating Engines Conference September 18-19, 19, 2007 Downey, California Technologies for Addressing Potential Barriers and Opportunities in California

AGENDA Engine Population and Background The

Single point injection systems Potential Barriers

Carburetor Sensors (O2, Temperature, Pressure,

(OBD) Findings What Works Example: Electronic

2 AGENDA Engine Population and Background The Opportunity Overview of Air/Fuel Ratio Tech Using Single point injection systems Potential Barriers and Solutions Fuel Control Valve Mixer / Carburetor Sensors (O2, Temperature, Pressure, other) Control Algorithms Embedded Diagnostics (OBD) Findings What Works Example: Electronic Controlled Gas Carburetor (EGC2) Closing and Questions Continental Controls Corp 2

3 Engine Population and Background Small Engines manufactured by GM, FORD, CUMMINS, ARROW, CAT, others. Many are NG or LPG versions of popular automotive types (e.g. 5.7L GM and 300 CI Ford CSG 649) PSI BMEP Most applications are direct drive of pumps (for AG) or gas compressors, pump-jacks, etc. Equipped with diaphragm-type carburetors set to operate rich. Most have no emissions controls: no after-treatment treatment or air/fuel ratio control. Per unit HP small, but engine population is substantial in California, many California engines are in AG applications. Even more units currently diesel, likely phased out in California due to attrition combined with PM limits from stationary engines and replaced with NG or LPG power units or electric drives. All engines will require some emissions controls to meet the 2008 EPA requirements. Most will require NSCR for 2008 EPA NSPS (2 g NOx / 4 g CO, 1 g NMHC) All will require NSCR for SCAQMD Requirements

4 Opportunity for Emissions Reduction Existing population of uncontrolled NG and LPG stationary engines > 2,000. > 1,100 engines in San Joaquin and Sacramento Valleys alone Typical NOx and CO levels: g/bhp-hour and g/bhp-hour respectively. Typically annual operating hours: 6-7,000. Average BHP 125 Emit ~ 17,000 Tons Per Year NOx ~ 20,000 Tons Per Year CO A/F controls alone with enhanced mixing can yield 70-80% reduction A/F controls with enhanced mixing and NSCR can yield 99% reduction or greater Population of uncontrolled, small, stationary diesel engines in Ag Service estimated at > 10,000

5 GM 5.7 Liter Natural Gas Engine 75 HP

6 Caterpillar 3306 Natural Gas Engine 145 HP

7 Overview of Air/Fuel Ratio Techniques Using Single point injection systems (as categorized by a fuel control manufacturer) Why is Air/Fuel Ratio Control Necessary: Optimize combustion to reduce emissions Control exhaust composition for best results with three-way catalyst (NSCR) Options for A/F Control with Single Point Injection Bypass System t Restrictor With Carburetor Full Authority Full Authority with Venturi Mixer

8 Control Techniques: Bypass System BYPASS CONTROLLER PRE CATALYST OXYGEN SENSOR CATAL LYST EXHAUST ENGINE PRESSURE REGULATOR SHUTOFF VALVE FUEL BYPASS VALVE CARBURETOR THROTTLE BODY AIR AIR CLEANER FUEL FUEL

9 Control Techniques Bypass System Method: Set Air/Fuel Ratio Lean Bypass Some Fuel Around Control Valve Advantages Keep Existing Carburetion / Mixer Arrangement Control Valve Sized for less than 100% fuel flow (smaller) Engine will operate in case of control valve failure (fail operational) Inexpensive Disadvantages Limited Control Range (Authority) Poor Response to Load Transients Equal or Worse Mixing than Carburetor Alone Possible requirement for manual pressure control ahead of gas control valve

10 Control Techniques: Full Flow - Restrictor Air / Fuel Ratio CONTROLLER ST CATALYS EXHAUST ENGINE PRESSURE REGULATOR SHUTOFF VALVE TROTTLE BODY FUEL CARBURETOR AIR AIR CLEA ANER

11 Restrictor System Control Techniques Method: All Fuel flows through control valve Valve Normally Open / Provides A/F Rich of λ=1.0 Restricts Fuel at Higher A/F s to Maintain Stoichiometric Ratio Advantages Keep Existing Carburetion / Mixer Engine will operate in case of control valve failure (fail operational) Inexpensive Lower Requirements for Valve Robustness Disadvantages Limited Control Range Poor Response to Load Transients Equal Mixing than Carburetor Alone

12 Control Techniques: Full Authority Air / Fuel Ratio CONTROLLER EXHAUST ENGINE PRESSURE REGULATOR SHUTOFF VALVE CONTROL VALVE FUEL TROTTLE BODY CARBURETOR AIR AIR CLE EANER

13 Full Authority System Control Techniques Method: All Fuel flows through h control valve Valve controls 0 100% of fuel flow Advantages Widest Range of lambda Best Response to torque /speed transients Highest Potential Control Resolution Disadvantages High Requirements for Valve Robustness Higher Cost Valve More sophisticated design

14 Elements of Most AFRC Systems Regardless of method, common principal elements of all systems: Fuel control valve Mixer Sensors Control Algorithm Diagnostics Typically, fuel control valve is modulated based on feedback from O2 sensor (NSCR) or feed back from AMP / engine HP and/or VE map (typical for PFI automotive and larger lean burn recip). Other Method for Closing the Loop: In the Exhaust before or after TWC High-speed Measurement of Exhaust Temperature Combined NOx/O2 sensors (NGK/NTK) Perhaps Post Cat for OBD In the Cylinder (Better!) High-Speed cylinder temperature Nexum Research (Laboratory test) Deutz (Production version for Lean Burn) ION Sense Upstream of Cylinder (Best) Air Flow + Fuel Flow Measurement (Expensive) Air Flow Surrogate (e.g. venturi throat pressure)

15 Potential Barriers Fuel Control Valve Customer Requirements Robustness long component life, 25,000 MTBO Resistance to contaminants: predictions are that pipeline gas quality may become less clean due to increased imports of LNG Imports will cause larger changes in average LHV (5-10%) Increased use of bio fuels Wellhead gas applications demand use of gas at site without substantial clean-up. Customer will not accept valve as maintenance item (catalyst, engine mechanical, ok) Responsiveness / Low Inertia to enable other control features (e.g. dithering) Low Power Consumption / low friction Environmental Requirements Safe for Explosive Environment Outdoor Rain / Weather / Sun Vibration and thermal cycling of on-engine mounted location

16 OPPORTUNITIES Fuel Control Valve ACTUATORS Stepper Motor High-precision: with encoder, absolute precision (Deutz) Slow, heavy, high power consumption Solenoid Operated High-power consumption Higher-speed cyclic control limited by energization of coil Pressure Regulators / Biased Pressure Regulator, etc Good stability, well proven technology Slow relative to other technology Trade-off between physical size and precision + cost Voice Coil Actuated High precision Lowest Power consumption Fastest Response Linear Behavior Inherently Deigned for Continuous cycling Duty

17 Carburetor retor System Potential Barriers Mixers A/F changes with air flow ( basic problem of carburetor system for TWC) Spring Diaphragm assembly is slow to respond Has numerous moving parts in contact with the air/fuel stream that require replacement and routine cleaning. Venturi Mixer No moving parts in contact with A/F stream If a certain constant gas injection pressure is maintained to the low pressure zone of venturi, the air/fuel ratio remains constant. Potential for extremely homogeneous mixing Very resistant to contaminants using multiple injection points Low pressure drop improves VE at WOT

18 Typical Gas Engine Carburetor

19 Prototype Electronic-Controlled Gas Carburetor

20 Narrow Band O2 Sensors - Switching Potential Barriers Sensors Heated (2 wire) Unheated (4 wire) Advantages Low cost Readily available No control required for heater circuit Disadvantages Difficult to control around unstable operating point Drift and aging, g, even between new sensors (infant deformities) Set-up with portable analyzer because of lack of accuracy of O2 indication Wide Band O2 Sensors lambda sensor All are heated, with heater control, power and signal output wiring (6-wire) Advantages Provides linear output proportion to oxygen concentration in exhaust Can be calibrated to a known reference (atmosphere) Control of heater circuit results in less drift and longer useful life (better data longer) Generally offer superior robustness Disadvantages More expensive for complete system due to control of heater and processing of signal Not AS common as wide range sensors O2 Sensors General Response Time of O2 Sensors in Exhaust System Limits it Aggressiveness of Control Load Transients create upsets in A/F control and possible instability

21 Potential Barriers O2 Sensors

22 Potential Barriers Software Control Algorithms Integral, PI or PID control on O2 sensor feedback is limited. Response Time of O2 Sensors in Exhaust System Limits Aggressiveness of Control Load Transients create upsets in A/F control and possible instability leading to large emissions excursions. Because of the limited control possible with exhaust oxygen sensors, large margins are necessitated to ensure compliance (larger TWC) There is a need to develop, general purpose, predictive simulation models that can be adapted to different engine packages. Determine dynamic gains that t will avoid unwanted interaction ti with the speed governing system. Model the engine as a system knowing the air flow and having characterized the dynamic response of each component of the air/fuel system including sensors and fuel control valve. Characterization Test of Engine and driven equipment Considering the dynamic characteristics of the entire system including the control elements Validation testing of system on engine under controlled conditions

23 Potential Barriers Software Control Algorithms Modeling Manifold inlet & outlet flows are calculated and integrated to get manifold air mass from which manifold pressure is calculated using the equation of state for air. Inlet flow is calculated using the orifice flow equation for the air throttle, with parameters of throttle area, inlet and manifold pressure and air temperature. Outlet flow is determined by engine speed, manifold pressure and volumetric efficiency as a function of speed. Manifold outlet air flow to the engine is used to set fuel valve position set point. Fuel flow is metered by the fuel valve based on its dynamics and the fuel gas orifice flow equation Fuel pressure, manifold pressure, fuel valve position, etc are used to calc fuel flow Lambda is calculated from manifold outlet air flow and fuel flow Engine power and torque are calculated as functions of manifold outlet air flow, lambda and engine speed. Engine Power torque divided by total rotational inertia produces engine acceleration which is integrated to get engine speed. The governor controls speed with a PI or PID control based on the error between speed set point and actual speed.

24 Predictive Model Using VisSim Software Rapid Change in Throttle Snap Open

25 Findings What Works Software Algorithms Air/Fuel ratio control dynamics must have dynamic gain 2-3x above the speed controller to achieve stability with precise air/fuel control. Air/Fuel control has to be faster than speed governor. Seems apparent but this is contrary to how A/F controllers are usually (always) set-up Slow A/F creates two overshoots opposed to one. Setting the A/F control very fast, prevents the speed control from adjusting for changes in speed AND air/fuel ratio Optimal tuning of speed governor is PID control tuned using Z-N method. Optimal control of A/F found using GID control with adaptive gain on pressure control. Best Solution is for integration of speed and A/F loops

26 From Simulations Modeling, Develop Transfer Function for Engine Type and Dynamic Constants PI (D) Typical of Engine Speed Controls

27 From Simulations Modeling, Develop Transfer Function for Engine Type and Dynamic Constants GID Control Architecture Error Ki / s M Kd * s M / Error = [G*Ki/s] * [ (Kd/Ki) * s^2 +s/ki + 1] M / Error = [G*Ki/s] * {[ (s/f1) +1] * [(s/f2) + 1]} Where, for f1 << f2: f1 =~ Ki f2 =~ 1 / Kd Note: f1, f2 are lead compensation break frequencies in rad / sec for GID control

28 Findings What Works Software Algorithms The degree of Precision (repeatability) and Accuracy (how to close to actual O2 Setpoint) required to maintain A/F ratio within 1-5% of optimal λ require new approaches than currently practiced in industry. Fast control of A/F not possible using current O2 Sensors in the exhaust stream. Overall time constant too slow. Need to be closer to the air/fuel process. In cylinder measure of A/F (Pressure, Ions, Temperature) e) or Upstream of engine Use a venturi

29 Diagnostics: OBD Discern between Malfunction of AFRC, Engine or TWC problem AFRC: If one other control element is use, e.g. pressure: By using pressure at venturi throat as the primary feedback loop. O2 sensor data can be used for a trimming signal or simply for monitoring only. Sampling of alarms: Pressure feedback out of range (pressure on the rail) O2 sensor out of range (O2 sensor on the rail) Increased pressure setpoint with no change on O2 setpoint Pressure feedback does not equal pressure setpoint for time period Pressure sensor fails to auto calibrate O2 sensor condition can be deduced from more reliable pressure transducer data Gradually increasing pressure setpoint, required for same O2 value indicative of plugged venturi holes or other condition ENGINE Low-cost method to distinguish between misfire and high exhaust O2 High-speed temperature monitoring ION Sense CATALYST Pre and Post Catalyst O2 sensors with high-frequency dithering uncertain effect on TWC life but useful health monitoring algorithm Combined NOx / O2 Sensor? Steady state Temperature rise? Other? How can we tell when the catalyst is healthy?

30 High-Speed Temperature Measurement* Combustion Instability Measurements Turbocharged Lean Burn Natural Gas Engine (1200 rpm, full load) 20 nstability (% %) Co ombustion I leaner Lambda Increase (%) *Courtesy of Nexum Research

31 Monitoring of TWC with two O2 Sensors Typical Dithering uses 1-55 Hz at +/- 5% of λ

32 Findings What Works Continental Controls Approach Using the EGC2 Use of full authority control valve actuated with voice coil Use of venturi designed to create excellent mixing of air and fuel. Fast PI control loop on gas injection pressure Maintains a constant gas injection pressure at the venturi throat to maintain constant mass ratio of air/fuel. Pure integral control on O2 sensor (if used) for trim and diagnostics. Gas control valve is extremely responsive (40ms slew rate). 25 corrections per second. Single component integrates all control electronics, control valve, venturi and user interface. Dithering at 1-5 5Hzat+/- 5% of λ possible but not implemented at this time

33 Control Schematic Diagram ELECTRONIC CONTROLLED GAS CARBURETOR ELECTRONIC CONTROLLED GAS CARBURETOR MODBUS / CANBUS COMMS O2 SENSOR SET POINT PRESSURE SET POINT Fuel gas supply 3-15" wc O2 SENSOR INPUT INTEGRAL CONTROL PROPORTIONAL & INTEGRAL CONTROL FULL AUTHORITY GAS CONTROL VALVE POWER 12 VDC GAS INJECTION PRESSURE TRANSDUCER INLET AIR TO ENGINE DISCRETE I/O VENTURI

34 Process Schematic Diagram ELECTRONIC CONTROLLED GAS CARBURETOR EXHAUST ENGINE THROTTLE BODY FUEL PRESSURE REGULATOR SHUTOFF VALVE AFRC EGC2 AIR AIR CLEANER

35 Production Electronic-Controlled Electronic Controlled Gas Carburetor

37 Prototype Electronic-Controlled Electronic Controlled Gas Carburetor

39 Example Performance Data Feedback Data from Bosch Wide Range O2 Sensor EGC2 Operating on Single Cylinder CFR Engine 3.9 Minute Run: Varying O2 Setpoint Single Cylinder 2-stroke Engine O2 Set-point O2 Feedback O2 Setpoint, Pr ress Feedback Constant Load / constant A/F Setpoint at Stoichiometric Constant Load / Varying A/F Setpoint Time (seconds x 10)

41 Gas Control Valve Summary Fuel control valve must be capable of providing long-life life in the presence of poor quality fuel gases. Use a full authority, fast-acting acting control for best transient response and highest- turndown ratio Also opens doors for dithering control Mixer Use of Venturi mixer in place of carburetor reduces pressure drop across carburetor. Improvements in VE at WOT Venturi provides opportunities for improvements in mixing and reduced maintenance requirements (no moving parts). Offers new control opportunity with gas injection pressure. CONTROL ALGORITHM Air/Fuel control loop must be much faster than speed control to avoid conflict and facilitate precise control. O2 sensor feedback alone is not sufficient for the precision or accuracy required for NSPS 2010 or SCAQMD requirements. By using pressure at venturi throat as the primary feedback loop. Poorer quality O2 sensor data can be used for an integrating trimming signal or simply for monitoring only.

42 Summary DIAGNOSTICS Basic need to understand source of the high emissions levels: AFRC, ENGINE or TWC OBD should be straight forward for the operator and provide alarms appropriate to the application. Use the MIL as model for smaller engines. Utilizing flow or flow surrogate such as gas injection pressure to venturi as primary control signal, permits wide range of cross checks with O2 sensor. O2 sensors can be used for catalyst monitoring if a dithering control scheme is utilized. Monitoring of TWC with Combined NOx/O2 sensor.

43 Questions?

Corporation rfisher@continentalcontrols.

44 Thank-You! For More Information Please Contact: Rick Fisher, Vice President Sales and Marketing Continental Controls Corporation John Vronay, President Vronay Engineering Services Corporation

SECTION 2.05 FUEL SYSTEM DESCRIPTION FUEL SYSTEM COMPONENTS

SECTION 2.05 FUEL SYSTEM DESCRIPTION FUEL SYSTEM COMPONENTS The engine fuel system consists of the following engine mounted components: Carburetors Throttle valves Fuel pressure regulator and balance line(s)