Design and analysis of the organic rankine cycle for a medium power vehicle diesel engine under realistic constraints

In the world and our country, the medium power diesel engines are widely used in trucks and construction equipment. In these engines, a large amount of energy is released into the atmosphere with the exhaust gases. In this study, the design and thermodynamic analysis of ORC were performed by considering the realistic limitations and the approaches for recovery of the waste heat in the exhaust gas. The experimental data of a turbocharged 6-cylinder diesel engine with a power of 261 kW were used in the design and analysis. Since mobile systems are targeted in the study, security, dimensional constraints and irregularity of the energy source are taken into account as challenging effects on the design. Basic ORC has been preferred to reduce the size of the system. Potential working fluids have been chosen among those that are non-flammable and have the lowest environmental hazards. In the cycle analysis, the performances of three different working fluids (R123, R141b and R245fa) were analyzed comparatively. It has been observed that as the speed of the diesel engine increases (1300, 1600, 1900, 2200 rpm), the temperature of the exhaust gas decreases while the flow rate increases. Despite of the decrease in the temperature of exhaust gas, the increase in the flow rate increased the net power gain in the cycle. The maximum thermal efficiency and net power obtained with R141b working fluid are 15.24% and 21.53 kW, respectively. In addition, the mass, volume and cost calculations were made for the basic components of ORC systems with net power recovery of 5, 10 and 15 kW at 1600 rpm engine speed with R141b working fluid. As a result of the study, it has been observed that the additional power can be provided at rates varying between 5.42% and 8.25% depending on the engine speed and the working fluid used, when the exhaust gas waste heat is recovered with the basic ORC. In addition, it was determined that the weight and volume of the ORC system required for 15 kW net power recovery is approximately 0.6% of the weight and volume of long haul trucks.