Design and performance analysis of an 8.7-liter E100-fuelled SI engine integrated with an ORC waste heat recovery system for genset applications

This study presents the design and performance of a turbocharged, 6-cylinder, 8.7-liter Spark Ignition (SI) Internal Combustion Engine (ICE) fueled by pure ethanol (E100) and integrated with an Organic Rankine Cycle (ORC) Waste Heat Recovery (WHR) system. A 1D numerical model of the engine was developed in the GT-Suite simulation environment, embedding a detailed description of the intake and exhaust manifolds and utilizing a 0D Turbulent Entrainment Combustion (TEC) model carefully set up for E100 fuel, and was experimentally validated. Genetic algorithms were employed to identify 30 optimal operating conditions across three engine speeds (i.e. 1000, 1500 and 2000 rpm) and a wide range of throttle valve openings (i.e. from 15% to 100% Wide-Open Throttle (WOT)), under stoichiometric conditions. Simulation results showed the engine achieved a minimum Brake Specific Fuel Consumption (BSFC) of 342.1 g/kWh, producing 232.6 kW of brake power and 37.95% of brake efficiency at 1500 rpm and 100% WOT. The highest brake power, exceeding 326.3 kW, was observed at 2000 rpm and 100% WOT, resulting in a BSFC of 345.3 g/kWh and a brake efficiency of 37.6%. Additionally, to explore the potential of the WHR system, a preliminary thermodynamic analysis was conducted using the Thermoflex simulation tool. The WHR system was based on a simple ORC layout, featuring two radial turbines in series and utilizing the same E100 fuel as the organic working fluid. Simulation results showed an increase in the overall mechanical power up to 262.4 kW, resulting in an overall mechanical efficiency of 42.8% with an increase both in brake efficiency and power of 12.8% at the design operating point.