Inverted Brayton Cycle as an Option for Waste Energy Recovery in Turbocharged Diesel Engine
To be published on September 9, 2019 by SAE International in United States
Energy recovery in reciprocating internal combustion engines (ICE) is one of the most investigated options for the reduction of fuel consumption and GHG emissions saving in the transportation sector. In fact, the energy wasted in ICE is greater than that converted in mechanical form. The contribution associated to the exhaust gases is almost one third of the fuel energy, calling for an urgent need to be recovered into mechanical form. An extensive literature is oriented toward this opportunity, strongly oriented to ORC (Organic Rankine Cycle)-based power units. From a thermodynamic point of view, one option, not extensively explored, is certainly represented by the Inverted Brayton Cycle (IBC) concept and by the corresponding components which make possible this recovery. IBC is a thermodynamic (exhaust) gas cycle which considers an expansion (made by a turbine under the ambient pressure), an isobaric cooling and a compression in sequence which restores the pressure which is needed to evacuate the exhaust gases toward the atmosphere. Thanks to the expansion which decreases the pressure below the ambient pressure, mechanical work produced used to move the compressor and to produce useful power associated to the remaining part. This can be possible thanks to the higher temperature of the exhaust gas with respect to the ambient value. In fact, the IBC working fluid is the exhaust gas itself. In this work, an assessment of the opportunity to bottom an IBC to an IVECO F1C 3.0L turbocharged diesel engine has been investigated, evaluating the most important parameters that affect the mechanical recovery. The integration between the bottomed IBC group and the existing variable geometry turbocharger has been proposed, representing the integration a novelty in the sector. In fact, this allows to enhance the recovery without modifying the pressure’s map of the charge air (required by the engine).