Low Frequency Acoustic Modeling of the Intake System of a Turbocharged Engine and the Exhaust of a Dual System William Seldon, Jamie Hamilton, Amer Shoeb - General Motors Jared Cromas, Daniel Schimmel - Gamma Technologies
Introduction Concerns about accuracy for turbocharged engines Multiple encounters of specifications saying 1D simulation can't handle turbocharged engine acoustics No data to support this GM decided it was worth looking into in more detail Concerns about modern exhaust features, like X-pipe Some newer features are not as straight forward in a 1D model GM decided an X-pipe was worth investigating 2
Experimental Setup - Engine Selection Engine in vehicle, Mature engine (good engine model) Intake System Study Turbocharged I4 Engine Bore 86.0 mm Stroke 86.0 mm Displacement 2.0L Compression Ratio 9.5:1 Rated Power 270 hp @ 5500 rpm Rated Torque 400 Nm @ 3000 4600 rpm Exhaust System Study Naturally Aspirated V8 Engine Bore 103.25 mm Stroke 92 mm Displacement 6.2L Compression Ratio 11.5:1 Rated Power 455 hp @ 6000 rpm Rated Torque 625 Nm @ 4600 rpm 3
Experimental Setup - Intake System Throttle Body Multiple pressure locations Compressor housing installations Microphone at snorkel (inlet) Pressure Transducer Inlet Port Pressure Transducer Outlet Port Thermocouple Inlet Thermocouple Outlet Pressure Transducers Magnetic pickup or accelerometer for compressor speed Pressure Transducer Thermocouple FLOW Snorkel Airbox Compressor Hx Microphones Thermocouples Exhaust System Turbine 4
Experimental Setup - Exhaust System 16 Kiel probes 18 K-type thermocouples 2 condenser microphones at tailpipe RP1 RT1 RP2 RT2 Conditions Run Full load sweep, 20 s With Muffler Full load peak torque (4400 RPM) Full load peak power (6000 RPM) Full load sweep, 20 s Straight Pipes Full load peak torque (4400 RPM) Full load peak power (6000 RPM) RP6 RT6 RP7 RT7 RP8 RT8 MicR RP3 RT3 RP4 RT4 RP5 RT5 RT9 LT9 LP1 LT1 LP2 LT2 LP3 LT3 LP4 LT4 LP5 LT5 LP6 LT6 LP7 LT7 LP8 LT8 MicL 5
Intake Analysis - Overheating Engine Initial comparison not good, turns out engine was too hot With other data, model could be modified Adjust boost pressure, intercooler, air-to-fuel ratio The power of serial data 6
Intake Analysis - Predictive Modeling Intake system components fully predictive 7
Intake Analysis - Acoustic Compressor Novel compressor model Captures resonance effects of housing Improves acoustic response Small effect on engine calibration 8
Intake Analysis - Results Improved prediction of intake noise for a turbocharged engine 9
Exhaust Analysis - System Geometry GEM3D used to model manifolds, mufflers, and X-pipe Engine model updated with latest vehicle calibration Cam timing, spark/ignition timing, etc. Temperatures adjusted using wall solver 10
Exhaust Analysis - X-Pipe Requires further detail than 1 flowsplit with correct angles Flow pattern is mostly straight, Less forced mixing Out-of-phase oscillating flow in an X-Pipe (GT-POWER+ConvergeLite) 11
Exhaust Analysis - Results Good correlation to measured data Overall and Order content predicted well 20 20 20 20 20 20 12
Conclusions Good acoustic predictions can be made using a 1D model Complex geometries need to be modeled in detail Air boxes, intercoolers, X-pipes, mufflers Affects wave reflections (acoustics) not flow loss (performance) Elements do not require "calibration", all geometry based Temperature (Speed of Sound) has significant effect on noise Exhaust temperatures need be fairly accurate Novel compressor model used to increase accuracy Testing conditions need to be monitored closely Simulation can be modified to match unexpected test 13