Evaluation of Brayton and Rankine Alternatives for Diesel Waste Heat Exploitation

Abstract

A diesel engine may produce exhaust-gas thermal energy in excess of that needed for turbocharging. Alternatives for exploitation of the energy by producing work may be direct expansion through a gas turbine (completing a Brayton cycle that begins with the engine’s compression and combustion), or transfer of heat into a Rankine cycle. It is demonstrated that either alternative may have a domain in which it is superior in work done, or in exhaust volume per unit mass of diesel exhaust. Computation models are developed and demonstrated for finding the boundaries along which the Rankine and Brayton alternatives have equal merit in either work or exhaust volume.