Effect of the Exit Pressure Pulsation on the Performance and Stability Limit of a Turbocharger Centrifugal Compressor

Transcription

1 Effect of the Exit Pressure Pulsation on the Performance and Stability Limit of a Turbocharger Centrifugal Compressor Maria E Barrera-Medrano Imperial College London, Department of Mechanical Engineering 25 th April, 2017

2 Contents I. Research overview and scope II. III. IV. Development of purpose-built experimental facility Experimental investigation of pulsating flow conditions on surge margin Analysis of experimental data V. Data correlation Prediction of SMI (Surge Margin Improvement) 2

3 Pressure ratio [-] I. Research overview and scope What is Surge and why is it important? Constant Efficiency Islands Intake Valve Engine Line Air flow ratio [-] Constant Speed Lines 1 Compressor Inlet 2 Compressor Discharge 3 Charge Air Cooler (CAC) 4 Intake Valve 5 Exhaust Valve 6 Turbine Inlet 7 Turbine Outlet 3

4 Contents I. Research overview and scope II. III. IV. Development of purpose-built experimental facility Experimental investigation of pulsating flow conditions on surge margin Analysis of experimental data V. Data correlation Prediction of SMI (Surge Margin Improvement) 4

5 II. Development of purpose-built experimental facility Build a technology for compressor performance measurement under pulsation. L D INLET = Pulsating Flow Device Throttling System AIR FLOW L D OUTLET =

6 II. Development of purpose-built experimental facility Pulsating Flow Device Main components V1 V2 6

7 II. Development of purpose-built experimental facility Pulsating Flow Device Variable Plenum Volume and Pulse Generator D in Plenum Volume Pct. relative to 16L diesel engine Capacity [L] Minimum, V min 50% 8.48 Intermediate, V med 100% Maximum, V max 160% Disc size for reference condition D65 65% total inner pipe area (D in ) Fully closed (left) Disc area [mm 2 ] 2964 Free flow area [mm 2 ]

8 II. Development of purpose-built experimental facility Pulsating Flow Device SUITABILITY in reproducing engine conditions A T = 1 f Engine test scenario (set by sponsor company): 2000 rpm (66.67Hz) 8

9 Contents I. Research overview and scope II. III. IV. Development of purpose-built experimental facility Experimental investigation of pulsating flow conditions on surge margin Analysis of experimental data V. Data correlation Prediction of SMI (Surge Margin Improvement) 9

10 III. Experimental investigation of pulsating flow conditions on surge margin Experimental Test Conditions Throttling characteristics for data-logging: 1 Surge/ near surge point 2 Peak pressure point 3 High efficiency point 4 Large flow/near choke Speed-line under study: rpm Reference operating condition in this study equivalent to such of an engine operating at low speed (operating condition set by sponsor company): Pulse frequency 66.67Hz (2000rpm) Pulse amplitude Rotary disc D65 Pulse location Compressor outlet Plenum volume Intermediate V P 10

11 III. Experimental investigation of pulsating flow conditions on surge margin Time lapse between data points is constant, however data points are not equidistant There are regions where the movement within hysteresis loop is slower (high density of points) Hysteresis behaviour Pressure and VFR evolution against time A A B A B The location of the unsteady averaged point (blue) is guided by the density of the points describing the instantaneous behaviour (red) of the system for a given time. 11

12 III. Experimental investigation of pulsating flow conditions on surge margin REFERENCE CONDITION (Intermediate V P, 66.67Hz) Averaged point evaluation 8.55% 10% 12

13 III. Experimental investigation of pulsating flow conditions on surge margin REFERENCE CONDITION (Intermediate V P, 66.67Hz) Instantaneous point evaluation 13

14 III. Experimental investigation of pulsating flow conditions on surge margin Plenum volume effect on the surge margin (steady and unsteady conditions) V P PLENUM VOLUME EFFECT V P [m 3 ] V1 FREQ Minimum V P, 66.67Hz (2000rpm) Intermediate V P, 66.67Hz (2000rpm) Maximum V P, 66.67Hz (2000rpm) Frequency effect on the surge margin For the steady evaluation, the rotary valve is disabled and kept on its fully open position V1 FREQUENCY EFFECT V P [m 3 ] V1 FREQ [Hz] Intermediate V P, 100Hz (3000rpm) Intermediate V P, 66.67Hz (2000rpm) Intermediate V P, 43.33Hz (1300rpm) Intermediate V P, 30Hz (900rpm) Intermediate V P, 20Hz (600rpm) 14

15 III. Experimental investigation of pulsating flow conditions on surge margin COMPRESSION SYSTEM CHARACTERIZATION Characterization of the compression system by means of the stability parameter B, defined by Greitzer (1976) Equivalent Compression System B = 2L a U = U A c 2L ω H V P L C ω H Helmholtz frequency; a Speed of sound (m/s) Stability parameter, B = U ρua = ρ U2 2 A 2ω H L ρua ρaluω H = COMPRESSOR PRESSURE RISE CAPABILITY INERTIAL FORCES Compression System under study Volume Percentage relative to baseline engine V P [m 3 ] Minimum V P 50% Intermediate V P 100% Maximum V P 160% B

16 Contents I. Research overview and scope II. III. IV. Development of purpose-built experimental facility Experimental investigation of pulsating flow conditions on surge margin Analysis of experimental data V. Data correlation Prediction of SMI (Surge Margin Improvement) 16

17 IV. Analysis of experimental data Experimental Test Conditions (summary) Throttling characteristics for data-logging: 1 Surge/ near surge point 2 Peak pressure point 3 High efficiency point 4 Large flow/near choke Speed-line under study: rpm Reference operating condition in this study equivalent to such of an engine operating at low speed (operating condition set by sponsor company): Pulse frequency 66.67Hz (2000rpm) Pulse amplitude Rotary disc D65 Pulse location Compressor outlet Plenum volume Intermediate V P 17

18 IV. Analysis of experimental data VOLUME EFFECT on surge margin STEADY EVALUATION I. As suggested by Greitzer (1976), the lower the volume in the system is, the better surge margin (lower flow values). II. III. As the volume in the system is decreased, the inertial forces are dominant Based on Greitzer s lumped parameter model, the inertial forces relate to a time lag in the onset of flow instability, and hence, the compressor is able to operate towards lower flow values. 18

19 IV. Analysis of experimental data VOLUME EFFECT on surge margin AVERAGED UNSTEADY EVALUATION I. No clear trend, but in any case the surge margin improves when compared to the equivalent steady condition ( Q interm VP, Steady=0.375 m 3 /s) II. III. Minimum followed by maximum volume achieve the best results on surge margin. When considering maximum volume case, there is an important penalty on pressure rise. 19

20 VOLUME EFFECT on surge margin INSTANTANEOUS UNSTEADY EVALUATION #1- Surge #2 Peak PR #3 Peak efficiency #4 Large flow

21 IV. Analysis of experimental data FREQUENCY EFFECT on surge margin AVERAGED POINT I. Throttle fixed II. III. IV. Important shift on operating point caused by pulse frequency Typical low speed range of an engine varies between 1200 to 2000rpm 40 to 66.67Hz Wide evaluation considering higher and lower limits of the typical engine operating range (20-100Hz) 21

22 IV. Analysis of experimental data FREQUENCY EFFECT on surge margin AVERAGED POINT Engine low speed range ( rpm) Surge margin: Steady condition Intermediate V P I. Surge margin improvement for all cases when compared to steady condition (dotted line) ( Q interm VP, Steady=0.375 m 3 /s) II. Results within typical low speed engine range present the best improvement : Hz III. IV. Considering out of limit cases : best result achieved with pulse frequency of 100Hz, worst result achieved with 20Hz. Overall evaluation the greatest surge margin improvement achieved by a pulse frequency of 43Hz. 22

23 FREQUENCY EFFECT on surge margin INSTANTANEOUS POINT #1- Surge #2 Peak PR #3 Peak efficiency #4 Large flow

24 Contents I. Research overview and scope II. III. IV. Development of purpose-built experimental facility Experimental investigation of pulsating flow conditions on surge margin Analysis of experimental data V. Data correlation Prediction of SMI (Surge Margin Improvement) 24

25 V. Data correlation Prediction of SMI CORRELATING EXPERIMENTAL DATA Matrix of experimental data based on the surge margin improvement (SMI) for all possible combinations of: Pulse frequency 20Hz, 30Hz, 43Hz, 66.67Hz and 100Hz Pulse amplitude D35, D65 and D80 Plenum volume Minimum V P, intermediate V P and maximum V P SMI % = Q surge,steady Q surge,pulsating Q surge,steady 100 Disc - D Hz Hz 43 Hz 30 Hz 20 Hz Minimum V P x x x x x Intermediate V P x x x x x Maximum V P x x x x x Disc D Hz Hz 43 Hz 30 Hz 20 Hz Minimum V P x x x x x Intermediate V P x x x x x Maximum V P x x x x x Disc D Hz Hz 43 Hz 30 Hz 20 Hz Minimum V P x x x x x Intermediate V P x x x x x Maximum V P x x x x x 25

26 V. Data correlation Prediction of SMI CORRELATING EXPERIMENTAL DATA Multi-parameter linear regression analysis SMI % = Q surge,steady Q surge,pulsating Q surge,steady 100 Correlation based on the relationship between the following four non-dimensional parameters: Pulsation flow coefficient: Pulse frequency: Plenum volume: Pulse amplitude: φ = Q 3 N D tip f = f tested f ref = f tested Hz VR = AR = V P V P,intermediate A free flow,disc A outlet,compressor 26

27 V. Data correlation Prediction of SMI CORRELATING EXPERIMENTAL DATA Multi-parameter linear regression analysis SMI [%]= Δφ 23.04f 10.57VR 39.03AR Δφ Δφ f 15.39Δφ VR Δφ AR+1.84f f VR+29.7f AR VR VR AR AR 2 Correlation capable of quantifying the impact of a pulsating state on the compressor surge margin using the pulse characteristics as the input for the prediction. The limits of the bounds of this polynomial fit are as follows: Pulsation flow coefficient: < Δφ < 0.32 Pulse frequency: 0.3 < f < 1.5 Plenum volume: 0.5 < VR < 1.5 Pulse amplitude: 0.2 < AR <

28 Acknowledgement The authors would like to thank: Publications: 1,2 Effect of the Exit Pressure Pulsation on the Performance and Stability Limit of a Turbocharger Centrifugal Compressor. Turbo Expo ASME 2016, Seoul, South Korea. 1 Paper published in the ASME Journal of Engineering for Gas Turbines and Power, vol. 139, Issue [DOI: / ] 2 Nominated for Best Paper Award, ASME th April, 2017

29 Maria E Barrera-Medrano PhD Student/Research Assistant Department of Mechanical Engineering Imperial College London Exhibition Road London SW7 2AZ Tel: +44 (0) Mob: +44 (0) m.barrera-medrano@imperial.ac.uk Web: Thank you for listening! Any questions?