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

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 >3,000 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.

4. 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

6. Example Two-Stroke Integral Compressor Engine

7. 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

8. Typical Control Strategy for Integral Compressor Engines

9. 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

10. Variation in Compression & Combustion Pressure Clark HBA-6T TGP Station 823

11. 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.

12. 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 => 0-5v output • < 30 msec response time • NOX measurement accuracy is ±5ppm of reading

15. Calibration on GMVH Engine - NOX Concentration

16. Calibration on GMVH Engine - Equivalence Ratio

17. 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.

18. Advanced Control Strategy for Integral Compressor Engines Not Shown: Individual Cylinder Firing Pressure Sensors

19. 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 R&D technologies

21. 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

22. 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

23. 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

24. Project Schedule

25. 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