Highly transient gas engine operation from a turbocharging perspective

Transcription

1 HERVÉ MARTIN, ABB TURBO SYSTEMS LTD Highly transient gas engine operation from a turbocharging perspective 10th CIMAC CASCADES, Kobe, 12 th October 2018

2 Overview Introduction Basics of load pick-up Modeling and simulation Simulation results Summary Outlook October 18, 2018 Slide 2

3 Introduction Lean burn gas engines for electricity generation Why Gas-engines instead of Diesel? Infrastructure availability (gas) Good compromise efficiency / emissions (NOx) Applications Electric Power Generation (EPG) Emergency gensets(hospitals, data centers, ) Operations Peak shaving Sudden power request Challenges Stringent acceleration requirements e.g. EPG Gas US data center: 60s start to full load Methane slip Emission requirements October 18, 2018 Slide 3

4 Basics of load pick-up Example: acceleration of gas engine from start-up to full power load pick-up idling + synchronization start start Ambient pressure idling + synchronization load pick-up Time Time October 18, 2018 Slide 4

5 Basics of load pick-up Compressor behavior Initial transient phase, missing energy on exhaust side (turbine inlet) turbocharger lag Compressor stays initially at constant speed, and pressure ratio drops below 1 Standard operation line is also shown for illustration purpose only Pressure ratio standard operation line const. speed lines const. efficiency lines 1 transient operation Volume flow rate / October 18, 2018 Slide 5

6 Basics of load pick-up What is turbo lag? Influencing parameters Volumes inertia (time to fill manifolds) Heat absorption in exhaust system in cold / hot conditions Turbocharger inertia (inertia of rotating components) Proper modeling of engine & turbocharging system necessary Analysis & identification improvement potentials Optimization of main parameters October 18, 2018 Slide 6

7 Modeling and simulation Compressor measurements Compressor measurements on thermodynamic testbench do not cover transient operating area Pressure ratio Low speed measurements are challenging Time to stabilized steady-state operation Internal heat transfers surge (instability) region measurement points choke region 1 transient operating area Volume flow rate / October 18, 2018 Slide 7

8 Modeling and simulation Compressor modeling ABB s compressor map model for off-design operation Physics-based compressor model Losses based on mathematical model single characteristics in incompressible region for tip Mach number 0.3 Calibration of the model at low speed still required At low speed, compressor operates in incompressible domain (like a pump) Only few measurements needed at low speed Definitions: Specific work:! "# $ % Flow coefficient: &! ' ( % $ Tip Mach number: ) $! *+, -./01+*2 +3/.* 4, ! $ 89: October 18, 2018 Slide 8

9 Modeling and simulation Compressor map at off-design Extended map shows compressor characteristics down to Locked-rotor (zero speed line) Deep choke (pressure ratio 1) Pressure ratio Compressor map model covering whole operating area 1 efficiency line <! 25 % Volume flow rate / October 18, 2018 Slide 9

10 Modeling and simulation Turbine measurements During transient phase turbine operates off-design at very low blade speed ratios and pressure ratios Measurements on turbocharger test-bench cover only a small part of the turbine transient operating area Measurable area limited by the compressor limits (surge and choke) Definition: peripheral velocity Blade speed ratio = isentropic gas velocity October 18, 2018 Slide 10

11 Modeling and simulation Turbine modeling From one-dimensional theory & measurements Quadratic trend of efficiency versus blade speed ratio, at constant pressure ratio G Zero efficiency at zero speed At low G, constant characteristics in incompressible region decreasing G October 18, 2018 Slide 11

12 Modeling and simulation Turbine modeling Turbine flow loss coefficient is a key parameter for transient operation Decreasing characteristic with blade speed ratio Variation limited in transient region Flow loss coefficients at zero speed measurable At low pressure ratio, turbine operates in incompressible region decreasing G Turbine map model covering whole operating area Definitions: Turbine flow loss coefficient! isentropic ideal mass flow rate actual mass flow rate October 18, 2018 Slide 12

13 Simulation results Boundary conditions Premixed gas engine 1-stage turbocharger Recirculation bypass Brake mean effective pressure: 22 bar Constant speed (grid parallel operation) Volumetric efficiency: 0.74 Air receiver Throttle valve Cooler Compressor Air / Gas mixer Intake Engine Exhaust gas receiver Turbine Exhaust Exhaust gas waste gate October 18, 2018 Slide 13

14 Simulation results Comparison simulation measurements: load pick-up from cold conditions October 18, 2018 Slide 14

15 Simulation results Analysis and optimization of load response Reference (cold) Reference (hot) Cold+New TC matching Cold+New TC matching+enrichment October 18, 2018 Slide 15

16 Summary Results: Understanding of the physics of the turbocharging system essential Simulations of the engine load response needs to be as accurate as possible ABB simulation: contribution to a valuable analysis and optimization of load response Engine parameters (e.g. richness) Turbocharger (e.g. matching) Turbocharging system (e.g. cold vs hot conditions) October 18, 2018 Slide 16

17 Outlook Deeper analysis and further improvement possibilities Modeling turbocharging solutions: Impact on highly transient lean-burn gas engine operation CIMAC Congress 2019, Vancouver, Canada D. Imhof, H. Martin, O. Bernard, C. Mathey Comprehensive simulation study with different generic high-speed lean-burn gas engines in cold, preheated and hot engine conditions. Comparison of different measures in terms of efficiency and acceleration behavior (engine control, turbocharging concept, turbocharger designs, etc.) Comparison of ramp-up to full power output between 1-stage and 2-stage turbocharging system October 18, 2018 Slide 17

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19 Definitions Compressor tip speed: u! IJ Compressor specific work:! Compressor flow coefficient: &! Compressor tip Mach number: ) $! *0*K/.3*LK/,2 1LK3M. 4N7KO.5 *+, 4,..5! "# $ % -0/7P. 6/0Q OK*.! ' 4N7KO.55+KP.*.O R *+, 4,..5 ( % $ *+, -./01+*2 +3/.* 4, ! $ 89: Turbine blade sped ratio:,.o+,l.ok/ -./01+*2 +4.3*O0,+1 MK4 -./01+*2 Isentropic gas velocity: ideal velocity obtained by expending isentropically the gas at turbine inlet to turbine outlet pressure Turbine flow loss coefficient! isentropic ideal mass flow rate actual mass flow rate October 18, 2018 Slide 19