Advanced Compressor Engine Controls to Enhance Operation, Reliability,

1
Advanced Compressor Engine Controls to Enhance
Operation, Reliability, Integrity

• Project DE-FC26-03NT41859
• Gary D. Bourn
• Southwest Research Institute
• 12-16-2003

2
Presentation Outline

• Executive Summary
• Technical Overview
• Project Schedule

3
Executive Summary

• The gas transmission industry operates gt3,000
  integral engine compressors with a median age of
  40 years and a median size of 2000 horsepower.
  These engines pump at least half of the 23 TCF of
  natural gas presently consumed.
• The natural gas consumption is projected to
  exceed 30 TCF by 2020. While new pipelines and
  compressors will be installed to increase
  capacity, the reliability of the existing
  infrastructure is critical to meet the demand.
• Wholesale replacement of existing integral
  compressors is not economically feasible.
  Therefore, the integrity, capacity, emissions,
  and efficiency of existing units must improve to
  help meet the project growth.

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Executive Summary (cont.)

• New technologies are required to improve the
  older integral compressors, and these include
  combustion, ignition, breathing, and controls.
• Advanced control technologies are necessary for
  these older integral engines to meet impending
  emissions regulations, and achieve enhanced
  operation, integrity, and capacity for continued
  use in the U.S. natural gas transmission network.
• The objective of this project is to develop,
  evaluate, and demonstrate advanced engine control
  technologies and hardware, specifically
  closed-loop NOX emissions control, on a
  two-stroke integral gas compressor engine.

5
Technical Overview

• Current Engine Control Status
• Proposed Advanced Controls Technologies
• Project Co-Funder
• Test Bed
• Project Work Breakdown Structure

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Example Two-Stroke Integral Compressor Engine
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Typical Control Strategy for Integral Compressor
Engines

• Fuel Header Pressure is modulated to maintain
  engine speed - governor
• Controller adjusts Wastegate to modulate Air
  Manifold Pressure based on derived relationship -
  air/fuel ratio
• Linear relationship of Air Manifold Pressure as a
  function Fuel Header Pressure is derived
• Individual Cylinder Balancing usually done
  manually.
• Ignition Controller does not always communicate
  with Air/Fuel Ratio Controller

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Typical Control Strategy for Integral Compressor
Engines
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Two-Stroke Integral Engine Issues

• Open Chamber configurations w/ mechanical fuel
  admissions exhibit relatively high
  cylinder-to-cylinder cycle-to-cycle deviation
  in firing pressure
• These deviations contribute to higher NOX
  emissions, reduced fuel efficiency, reduced
  operating envelope, as well as increased stress
  peaks on the crankshaft
• Combustion instability often blamed on
  inconsistent fuel/air mixing - improved w/
  pre-combustion chambers enhanced mixing fuel
  injectors
• Data suggests imbalance between cylinders in
  airflow (trapped air mass), which would create
  air/fuel ratio variances
• Two-Stroke breathing highly dependent on
  instantaneous manifold dynamics port open
  duration
• Individual cylinder control is necessary to
  improve engine performance

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Variation in Compression Combustion Pressure
Clark HBA-6T TGP Station 823
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Advantages of Individual Cylinder Control
A/F Imbalance between cylinders leads to reduced
Knock Lean Limit margins, lower overall
efficiency, higher overall NOx emissions.
Overall NOx emissions skews toward rich cylinders
due to non-linear relationship with Equivalence
Ratio.
A/F Balance between cylinders gives increased
Knock Lean Limit margins, allowing more timing
advance leaner overall operation. This
improves the Efficiency-NOx tradeoff.
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Current Advanced Control Technologies

• Advantages of controlling to fuel/air equivalence
  ratio are being realized
• Current approaches involve calculated equivalence
  ratio from in-direct measurements mapping of
  NOX
• Parametric Emissions Monitoring (PEM)
• Advanced versions incorporate continuous cylinder
  pressure measurement tuned models to predict
  NOX
• Electronic fuel injection
• Offer increased control flexibility improved
  in-cylinder mixing of air/fuel charge
• Coupled w/ calculated equivalence ratio
  continuous cylinder pressure measurement

13
Proposed Advanced Control Technologies

• Utilize NGK-Locke sensor to directly measure
  exhaust NOX equivalence ratio (similar to
  automotive controls)
• More accurate real-time control can be achieved
• Reduced engine mapping required to tune control
  algorithm for specific engine model
• Generalizes control algorithm for easier
  application to different engine models
• NGK-Locke sensor provides both NOX O2
  concentration in exhaust
• O2 channel can be calibrated to Equivalence Ratio
  (like UEGO)
• Has been demonstrated in both spark-ignition
  diesel engines
• SwRI has demonstrated sensor performance in
  two-stroke integral compressor engines

14
NGK-Locke NOX / O2 Sensor

• Utilizes thick film ZrO2
• 5th generation type
• Integrated control electronics temperature
  compensation
• 14.0 /-0.5V power requirement
• Linear in O2 and NOX concentrations gt 0-5v
  output
• lt 30 msec response time
• NOX measurement accuracy is 5ppm of reading

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Calibration on GMVH Engine - NOX Concentration
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Calibration on GMVH Engine - Equivalence Ratio
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Proposed Advanced Control Technologies (cont.)

• Advanced control will take global NOX
  concentration input control engine to maintain
  this specific level w/ optimized efficiency on a
  cylinder-to-cylinder basis
• Most common engine configuration w/ mechanical
  fuel admission will be targeted
• Global Fuel Header Pressure still used for speed
  governing.
• Equivalence Ratio input used to modulate
  Wastegate.
• Spark Timing set for optimal efficiency trimmed
  globally (if necessary) to maintain NOX.
• Cylinder pressure input provides for
  trimming/biasing individual cylinder Spark Timing
  Fuel Flow for balancing of NOX. This feature
  will increase efficiency for a given exhaust NOX,
  increase operating range, improve mechanical
  integrity.

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Advanced Control Strategy for Integral Compressor
Engines
Not Shown Individual Cylinder Firing Pressure
Sensors
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Project Co-Funder

• Cooper Energy Services (CES) is not only
  providing co-funding to this project, but making
  available their research engine and expertise of
  integral compressor engines as an OEM.
• Cooper-Bessemer engines make up a large
  percentage of the integral compressor engine
  fleet
• CES previously contracted with SwRI to setup
  their GMVH-6 laboratory engine at SwRI
  facilities.

20
Engine Test Facility

• 330 rpm, 1350 bhp gas compressor engine
• Engine highly instrumented for RD technologies

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Engine/System Controls

• Rapid Prototype Electronic Control System
  (RPECS)
• Full-authority controller
• SwRI developed
• Commercially available
• Rapid algorithm development
• SwRI interfaces with well-known control system
  manufacturers to assist engine manufacturers with
  technology transfer

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Engine/System Controls

• Algorithm Software Development
• Classic Modern Control Algorithms
• Real-time Model-based Control
• Diagnostics for Service OBD
• Adaptive Learn Algorithms

• Advanced Signal Processing
• Source Code Development in Assembly, C, and
  Graphical Environments Such As Matlab/Simulink

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Project WBS

• 1.0 System Configuration
• 2.0 Baseline Mapping
• 3.0 Algorithm Development
• 4.0 Closed-Loop Control Evaluation
• 5.0 Data Analysis
• 6.0 Algorithm Schematic Development

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Project Schedule
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Conclusion

• The SwRI/CES team appreciates the support of DOE,
  looks forward to the opportunity to advance the
  state of the art in integral compressor engine
  controls
• Our goal is to develop technology that can be
  realistically cost-effectively implemented by
  the gas transmission industry to help meet the
  growing demand for natural gas, while meeting
  current future emissions regulations