An Investigation into the Effects of Engine Displacement and Geometric Compression Ratio on Downsizing of a Direct-Injection Spark-Ignition Engine

  • Niall Turner

Student thesis: Doctoral ThesisPhD


The Ultraboost engine set new boundaries on the specific performance which could be achieved with a downsized engine. This work expands on those results by exploring the maximum feasible performance from even smaller displacement (up to 70% Downsizing factor) and higher compression ratio. The reasons for the impressive performance of the Ultraboost engine under knocking conditions are investigated and assessment is made of ignition delay correlations in typical one -dimensional performance simulation models. In conclusion, both compression ratio and engine displacement are found to become limiting under different conditions, and both the engine's operating boundaries and choice of forced displacement system are shown to have a profound effect on maximum potential performance.
Date of Award16 Jun 2021
Original languageEnglish
Awarding Institution
  • University of Bath
SponsorsJaguar Land Rover Ltd
SupervisorSam Akehurst (Supervisor) & Chris Brace (Supervisor)


  • Downsizing
  • DISI
  • engine
  • ICE
  • compression ratio
  • Turbocharging
  • turbocharger
  • Supercharging
  • supercharger
  • Ultraboost
  • EGR
  • Knock
  • combustion
  • Jaguar Land Rover

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