First Principles Development of the Efficiency Limits of Roto-Compound Engines

The research sought to first solve several core questions in the science of engine efficiency with a rigorous first principles approach, and then to understand the efficiency potential of roto-compound engines. The research includes original contributions to fundamental and applied engine thermodynamics, cycle and combustion optimization, exergy analyses, and the study of rotary turbines and roto-compound engines. Foundations were first developed from fundamental thermodynamics including the Carnot Efficiency, irreversible entropy generation, irreversible exergy destruction, exergy balances, and exergy efficiency. Definitions for combustion exergy efficiency were developed and then utilized to define novel process and cycle exergy properties, the thermodynamic efficiency limit of engines and specific efficiency limits for compound, combined, combined compound and recuperated cycle engines. Ideal roto-compound cycles were introduced and compared with ideal turbo-diesel, Miller and turbo-compound cycles. Exact exergy analyses were developed with consistent cycle parameters and combustion to develop estimates for the effects of compression pressure, fuel equivalence ratio, peak cycle temperature and pressure, blow down, expansion and heat recovery on cycle efficiency. Roto-compound cycles were shown to offer the maximum possible efficiency through systematic minimization of losses. Roto-compound engine designs were then studied at the 400 kW level with optimization for engine size, speed, pressure, compression ratio, supercharger and turbine pressure ratios, thermal barrier temperatures and combustion duration. The final result estimated that a 2.0 litre 4-cylinder roto-compound engine operating at 3,600 rpm and 505 bar peak cylinder pressure could reach 60.4% brake thermal efficiency. The research demonstrated that novel rotary turbines have the potential to enable record levels of power density, efficiency and carbon saving, generating 25-33% of total power output from recycled thermal energy, while enabling an estimated 54-84% downsizing versus a commercial 12.8 liter turbocharged diesel engine.

Grantor dc:publisher

Oxford Brookes University

Author dc:creator

• Onstenk, David

Contributors dc:contributor

• Bonatesta, Fabrizio

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/pn1n-4p31

OAI identifier oai:identifier

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