Fuel efficiency optimization for a divided exhaust period regulated two-stage downsized SI engine

Bo Hu, Sam Akehurst, Chris Brace, Pengfei Lu, Colin D. Copeland, J. W. G. Turner

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

In our previous paper, a new gas exchange concept termed Divided Exhaust Period Regulated 2-stage (DEP R2S) system has been proposed. In this system, two exhaust valves in each cylinder are separately functioned with one valve feeding the exhaust mass flow into the high pressure (HP) manifold whilst the other valve evacuating the remaining mass flow directly into the low pressure (LP) manifold. By adjusting the timing of the exhaust valves, the target boost can be controllable whilst improving the engine's pumping work and scavenging is attainable which results in better fuel efficiency from the gas exchange perspective. This paper will continue this study by adding an appropriate knock model to examine the benefits this concept could bring to the combustion phasing. The results at full load showed that under knock limited spark advance (KLSA) and fully optimized exhaust valve timing condition, the DEP R2S system benefited from lower pumping loss and better scavenging due to the reduced backpressure and improved pulsation interference despite suffering from reduced expansion ratio and expansion work. The combustion phasing was advanced across the engine speed which is mainly attributed to the reduced residual and the reduced requirement of gross IMEP. The net BSFC was observed to improve by up to 3% depending on the engine operating points. At part load, the DEP R2S system could be used as a mechanism to extend the 'duration' of the exhaust valve. This will reduce the recompression effect of the exhaust residuals during the beginning and the end of the exhaust stroke compared to the original R2S model with late exhaust valve opening and early exhaust valve opening. In addition, increased internal EGR due to the increased overlap between the LP and the intake valve is also beneficial for the improved PMEP as the throttle can be further opened to reduce the corresponding throttling loss. The average net BSFC improvement is expected to be approximately 6-7%.

Original languageEnglish
Title of host publicationMicroturbines, Turbochargers and Small Turbomachines; Steam Turbines
Place of PublicationU. S. A.
PublisherAmerican Society of Mechanical Engineers (ASME)
PagesV008T23A012
Number of pages10
Volume8
ISBN (Electronic)9780791856796
DOIs
Publication statusPublished - Jun 2015
EventASME Turbo Expo 2015: Turbine Technical Conference and Exposition, GT 2015 - Montreal, Canada
Duration: 15 Jun 201519 Jun 2015

Conference

ConferenceASME Turbo Expo 2015: Turbine Technical Conference and Exposition, GT 2015
CountryCanada
CityMontreal
Period15/06/1519/06/15

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ASJC Scopus subject areas

  • Engineering(all)

Cite this

Hu, B., Akehurst, S., Brace, C., Lu, P., Copeland, C. D., & Turner, J. W. G. (2015). Fuel efficiency optimization for a divided exhaust period regulated two-stage downsized SI engine. In Microturbines, Turbochargers and Small Turbomachines; Steam Turbines (Vol. 8, pp. V008T23A012). U. S. A.: American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/GT2015-43023