Optimising Aeristech FETT (Fully Electric Turbocharger Technology) for Future Gasoline Engine Requirements

Transcription

1 Optimising Aeristech FETT (Fully Electric Turbocharger Technology) for Future Gasoline Engine Requirements Dr Sam Akehurst, Dr Nic Zhang 25 th April

2 Contents Introduction to the Fully Electric Turbocharging Technology. Modelling approach and controllers. Difficulty of the single stage arrangement. Two stage arrangement. Transient performance. Project progress. Conclusions and further work. 2

3 Introduction to FETT Mechanically decoupled turbomachinery. Power transferred through electrical connection. Potential to improve aerodynamic efficiency, combustion efficiency and transient response. Independent control of turbo-machinery sizing Re optimisation of turbo-machinery Better efficiency Less constrained w.r.t. inertia for transient response Losses in electrical power transfer Shafts are very efficient! 3

4 Modelling approach 2 litre single stage turbocharged gasoline engine as GT power base model. Base model calibrated for full load, partial load and transient performance. Turbomachinery maps from CFD calculation of 3D design used for electric compressor and turbine. Simulation plan. Full load torque curve achieving 350Nm and 240PS. Partial load BSFC map. Drive cycle fuel economy using minimap points. Transient simulations. 4

5 Controllers Throttle Wastegate (two stage) Target: BMEP Range: Low load. Target: BMEP Range: Mid to high load. ecompressor eturbine Target: BMEP Range: Overboost at low end; transient. Bypass valve: Target: Turbine power map. Range: Map based (purple dashed line). eturbine speed: Target: polynomial speed model vs ER. Range: when eturbine active. =

6 Single stage arrangement De-throttles engine at part load. Reduce engine back pressure through use of large eturbine. Optimal engine packaging. Improves catalyst light off, etc.. However When applying the estimated FETT system efficiency of 65% (slightly pessimistic), boost & back pressure increase in a vicious circle. eturbine power cannot balance ecompressor power at low end. eturbine power increases to unrealistically high level at higher speed (~46kW). 6

7 Two stage arrangement Fuel economy benefit De-throttling through reduced throttle delta_p. Reduce pre-boost <- ecompressor. Throttle opens wider <- eturbine increases back pressure. eturbine power harvesting when economical. System Power level manageable at full load condition Mechanical turbocharger as main unit. ecompressor as peak unit: 3.4kW, eturbine: 5.2kW. If eturbine designed for 8kW: Potential to choose larger mechanical turbine, increasing FL power output, reducing part-load BSFC. Potential to down speed engine with redesigned gear ratio, further reducing BSFC. 7

8 Two stage arrangement Part load simulation - eturbine energy stored in battery for electrical auxiliary usage Engine brake torque remain the same. Evaluate system BSFC: = + 81% 81% System Engine 8

9 Two stage arrangement Part load simulation - eturbine energy sent to crankshaft through MHEV powertrain Engine torque needed from combustion is reduced. Engine BSFC = System BSFC. BSFC benefit diminishes due to: BISG efficiency. For same torque output, IMEP moves to low efficiency region. Still great potential! 9

10 Two stage arrangement Drive cycle minimap points Points reside in lower left region Using different cycle weighting: NEDC: -0.68% FTP: -0.96% HiWay: -2.6% WLTP: -1.14% RDE cycle to better show potential? 60% in NEDC weighting 10

11 Two stage arrangement Transient simulations 0 to 100 km/h acceleration Fast running model: good fidelity for transient study. Simulink GT Power Co-sim environment developed. Jaguar XE vehicle with ZF 8HP transmission modelled. 11

12 Two stage arrangement Transient simulations 0 to 100 km/h acceleration Gear shift strategy. 4 gears to get to 100 km/h. Gear shift at 6000 rpm. Shift duration = 200 ms. (ZF 8HP spec.) Throttle demand returns to 0 during shift. Engine speed during shift imposed. Inaccuracies. Vehicle details: inertias, etc. Shift manoeuvre. GT model. 12

13 Two stage arrangement Transient simulations 0 to 100 km/h acceleration Baseline results. Throttle starts transient at 3 sec. Engine speed reaches 6000 rpm and shift to next gear. Throttle reduces to 0 when shift gear. Engine torque shows large inertia force during shift due to model simplification yet does not influences result. Vehicle reaches 100 km/h at 6.64 sec. good correlation with 6.8 sec. vehicle spec. 13

14 Two stage arrangement Transient simulations 0 to 100 km/h acceleration FETT results. ecompressor activated for transient boost request. eturbine bypassed in the full duration. Throttle starts transient at 3 sec. Engine speed reaches 6000 rpm earlier. Advantage gained in the first 2 secs. Vehicle reaches 100 km/h at 5.61 sec. 1 sec. faster than baseline. ecompressor power consumption: 13 kj (8.3kJ in first 2 sec.). 14

15 Aeristech FETT esupercharger Summary Novel motor configuration (8-pole, high copper fill) 23% part-count reduction (vs previous model) 53% mass reduction (vs previous model) Fully integrated motor and controller High efficiency compressor design (80%) General Specification Compressor type Bearings Cooling Ambient air temperature Input voltage Mass Centrifugal Rolling Element - greased (for life) Water/glycol - 75 C (no derating) -40 C to 100 C (140 C Peak) 48V (nominal) < 2.8 kg Performance Max compressor speed Transient response Max pressure ratio Max flow Input power rpm < 0.35 seconds 0.07 kg/s PR 6.2kW (peak), 4.5kW (continuous) driving clean technology

16 Aeristech FETT Turbine-Generator Summary Turbine speed not synchronous with compressor High speed/ high temperature generator design Water cooled stator & bearing housing Oil-lubricated rolling element bearings High efficiency turbine wheel (76%) Electronic speed control to maximise system efficiency General Specification Turbine type Bearings Cooling Output Voltage Radial Oil-lubricated rolling element Water/glycol 48V (nominal) Performance Max turbine speed Expansion ratio Power Output rpm 1.9 (application dependent) >8kW (Shaft) driving clean technology

17 Conclusions Single stage Fully Electrical Turbocharging Technology on highly downsized engine is challenging due to high power rating as a result of electrical system efficiency limit. Two stage FETT is a more viable solution with great potential to improve the fuel economy at engine partial load condition. However the drive cycle minimap points cannot fully demonstrate the benefit of this technology. Transient response is expected to be substantially improved. Significant FE benefits appear to exist, particularly in real world driving and RDE scenarios Next steps Further drivecycle energy management work being undertaken Validation of compressor and e-turbine performance using gas stand at Bath 17

18 Thank you Any Questions? 18