Design and thermo-economic optimization of organic Rankine cycle for waste heat recovery of exhaust gas recirculation for heavy duty diesel engines

Nowadays the rise of fuel prices and global warming problems are making the renewable energy sector really active. But at the same time, we have to face the reality that being 100% independent from fossil fuel is not possible, at least for the close future. In America trucks move $600 billion in freight every year; more than 80% of all freight transportation revenue. Freight transportation is dominated by trucks and to think about alternative propulsion systems is impossible because the hybrid automotive sector has just recently started studying the heavy-duty vehicles (HD-vehicles). The only way to reduce the fuel consumption and the CO2 emissions of vehicles is by improving the engine efficiency. Thus, improving the engine efficiency is one promising solution to reduce the fuel consumption and the CO2 emissions of HD-vehicles. One of the techniques to achieve that, is to utilize the exhaust heat for extra-power production, since around 30-40% of fuel supplied energy is rejected to the ambient. A good way that deeply improves the engine efficiency is the waste heat recovery (WHR) system using Organic Rankine Cycle (ORC). Despite the success of the stationary WHR systems, challenges remain when applying the WHR technology for road transportation. The proposed approach focuses on fluid selection and design of optimization for a specific ORC configuration: Exhaust Gas Recirculation (EGR) waste heat recovery systems for Heavy-Duty diesel engines. In this system, the EGR cooler heat rejection is the primary heat source for our bottoming cycle. We pursued the best trade off among different factors: economic, thermodynamic and simplicity of the design which possibly doesn’t affect the nominal specifications of the whole combustion engine, like pressure and timing. Up to 5% improvement in fuel saving is possible by utilizing this simple and economic layout. From computer simulation it was concluded that degree of superheats, evaporator and condenser pressures, working fluids and heat sources significantly affect the ORC performance, efficiency of heat recovery and cost. This research has been developed at the Vehicle Dynamics and Control (VDC) Laboratory of Korea Advance Institute of Science and Technology (KAIST) thanks to the collaboration between KAIST and Politecnico di Milano.