Design methodology for radial turbo expanders in mobile organic Rankine cycle applications

A. W. Costall, A. Gonzalez Hernandez, P. J. Newton, R. F. Martinez-Botas

Research output: Contribution to journalArticlepeer-review

62 Citations (SciVal)


Future vehicles for clean transport will require new powertrain technologies to further reduce CO2 emissions. Mobile organic Rankine cycle systems target the recovery of waste heat in internal combustion engines, with the exhaust system identified as a prime source. This article presents a design methodology and working fluid selection for radial turbo expanders in a heavy-duty off-road diesel engine application. Siloxanes and Toluene are explored as the candidate working fluids, with the latter identified as the preferred option, before describing three radial turbine designs in detail. A small 15.5 kW turbine design leads to impractical blade geometry, but a medium 34.1 kW turbine, designed for minimum power, is predicted to achieve an isentropic efficiency of 51.5% at a rotational speed of 91.7 k min-1. A similar 45.6 kW turbine designed for maximum efficiency yields 56.1% at 71.5 k min-1. This emphasizes the main design trade-off - efficiency decreases and rotational speed increases as the power requirement falls - but shows reasonable radial turbine efficiencies and thus practical turbo expanders for mobile organic Rankine cycle applications are realizable, even considering the compromised flow geometry and high speeds imposed at such small scales.

Original languageEnglish
Pages (from-to)729-743
Number of pages15
JournalApplied Energy
Publication statusPublished - 1 Nov 2015


  • Bottoming cycles
  • Mobile organic Rankine cycle
  • Radial turbine
  • Toluene
  • Turbo expander
  • Waste heat recovery

ASJC Scopus subject areas

  • Building and Construction
  • Energy(all)
  • Mechanical Engineering
  • Management, Monitoring, Policy and Law


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