Modeling of an Organic Rankine Cycle Waste Heat Recovery system for automotive engine applications

Abstract

The remarkable investments made by manufacturers over the last few decades have contributed to improving the performance of internal combustion engines in every aspect: lower polluting emissions, greater specific power and thermal efficiency. Despite this, on an average, about 40% of the thermal power theoretically available from the combustion of the fuel is still stored in the exhaust gases and therefore dispersed in the environment. In this work the modeling and validation of a waste heat recovery (WHR) plant will be described, combining the engine with a low temperature Organic Rankine Cycle (ORC) system, in order to investigate the feasibility of this system on board of a vehicle, analyzing the quantity of thermal power recovered and made available in the form of electrical power. The ORC plant is modeled using a 0D/1D thermo-fluid dynamic approach. Starting from experimental tests, a map-based model for the piston pump and the scroll expander has been developed. The model has been validated through the use of a vector optimization technique, exploiting a genetic algorithm (MOGA). Subsequently, this system has been coupled to a spark ignition engine for automotive applications, adapting its speed range to comply with the ORC experimental tests. To have an accurate control over the expander inlet temperature, a bypass circuit and two throttles actuated by a PI controller have been implemented. The simulations were performed by considering 18 engine points at maximum load and different rpm. An average thermal efficiency increase of the system of 2.6% was obtained by introducing the recovery plant, and wide improvement chance can be foreseen in the case of ORC full-power use.

Model and transient Control strategy design of an Organic Rankine Cycle Plant for waste heat recovery of an Internal Combustion Engine

“…Finally, a plate heat exchanger condenses the organic fluid using cold water. The pump and the expander of the plant, which characteristics are reported in [16], are modelled using a map-based model approach, which sums up inside maps the working points extrapolated from experimental tests. The pipes and the heat exchangers are modelled through a 1-D approach, solving the mass, energy (enthalpy) and momentum balance equations for each timestep:…”

“…To pursue this aim, an ORC Power Plant is modelled using a 0D/1D thermo-fluid dynamic approach for the plate heat exchangers, evaporator and condenser and a map-based one for the piston pump and the scroll expander. The considered experimental apparatus of the ORC plant resides inside Purdue university's laboratory, in Indiana, which geometrical and experimental data of the components are reported in [16]. A novelty presented in this paper is the schematic approach used for the simulation of the evaporator and condenser.…”