Research Papers: Internal Combustion Engines

A Numerical Study of the Benefits of Electrically Assisted Boosting Systems

[+] Author and Article Information
Richard D. Burke

Department of Mechanical Engineering,
University of Bath,
Bath BA2 7AY, UK
e-mail: R.D.Burke@bath.ac.uk

Contributed by the IC Engine Division of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received January 28, 2016; final manuscript received February 1, 2016; published online April 5, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(9), 092808 (Apr 05, 2016) (9 pages) Paper No: GTP-16-1045; doi: 10.1115/1.4032764 History: Received January 28, 2016; Revised February 01, 2016

An electric compressor and an electrically assisted turbocharger have been applied to a 2.0 L gasoline and a 2.2 L diesel engine 1D wave dynamic model. A novel approach is presented for evaluating transient response using swept frequency sine wave functions and Fourier transforms. The maximum electrical power was limited to 6% of the maximum engine power (12 kW and 5 kW, respectively). The systems were evaluated under steady-state and transient conditions. Steady-state simulations showed improved brake mean effective pressure (BMEP) at low-engine speeds (below 2500 rpm) but electric power demand was lower (3 kW versus 8 kW) when the electric compressor was on the high-pressure side of the turbocharger. This was due to the surge limitation of the turbocharger compressor. The electrically assisted turbocharger offered little opportunity to increase low-speed BMEP as it was constrained by compressor map width. Rematching the turbo could address this but also compromise high-engine speeds. BMEP frequency analysis was conducted in the region of 0.01–2 Hz. This was repeated at fixed engine speeds between 1000 rpm and 2000 rpm. Spectral analysis of the simulated response showed that the nonassisted turbocharger could not follow the target for frequencies above 0.1 Hz, whereas the electrically assisted device showed no appreciable drop in performance. When assessing the electric power consumption with the excitation frequency, a linear trend was observed at engine speeds below 1500 rpm but more complex behavior was apparent above this speed where BMEP levels are high but exhaust energy was scarce.

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Fig. 1

Gas path layouts showing (a) preturbo electric compressor, (b) post-turbo electric compressor, and (c) electrically assisted turbocharger

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Fig. 2

Control for surge avoidance during steady-state simulations with electric compressor configurations

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Fig. 3

Control of transient simulations with electric compressor configurations

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Fig. 4

Control of transient simulations for diesel engine using electrically assisted turbocharger

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Fig. 5

Rapid load step transients showing throttle, waste-gate, and electric power control for standard and forced transients as well as an example BMEP response at 2000 rpm

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Fig. 6

Example swept frequency sine wave demand signal for varying frequency simulations

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Fig. 7

Example swept frequency sine wave demand signal for varying frequency simulations

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Fig. 8

Achievable BMEP depending on electric power source for electric compressor installations (a) before and (b) after the turbocharger on the research gasoline engine (validated combustion limitation shown in gray)

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Fig. 9

Compressor operating points for each e-booster configuration: (a) electric compressor and (b) turbocharger compressor

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Fig. 10

e-turbo operating showing surge problem due to compressor map width

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Fig. 11

Chirp results for VGT and electrically assisted turbocharger showing drop off at higher frequencies and recovery from e-turbocharger at 1750 rpm

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Fig. 12

FFT for each speed showing target, VGT, and e-turbo

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Fig. 13

Electric power against BMEP frequency for e-turbo application




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