Feasibility analysis and performance characteristic investigation of thermal energy storage system based on organic Rankine cycle for engine exhaust temperature modulation

The exhaust temperature of the engine has a significant impact on the conversion efficiency of the after-treatment. A thermal energy storage (TES) system with organic fluid for engine exhaust temperature modulation is established in this paper, and the performance characteristics of the TES system with the engine exhaust temperature modulation are analyzed based on the organic Rankine cycle (ORC). First, an accumulator-centered TES system model is established based on GT- SUITE, and the effects of working fluid mass, mass flow rate, supply strategy and working fluid type on the TES system are analyzed. Second, the influence of coupled ORC-TES system on exhaust emission and after-treatment efficiency is analyzed, and the cost-benefit analysis of integrated ORC-TES system is carried out. Finally, the simulation results show that with the increase in working fluid mass, the average temperature, availability, satisfaction, and comprehensive index (CI) of the TES system gradually decrease, while the standard deviation gradually increases. Simultaneously, the average temperature, availability, satisfaction, and CI of the TES system all increase with increasing working fluid mass flow rate for the same mass of working fluid. In the high-performance region (CI = 0.7 similar to 1.0), the modulating performance of exhaust temperature mainly depends on the mass of the working fluid supply. However, in the low-performance region (CI = 0 similar to 0.4), the sensitivity of mass and mass flow should be taken into account. In addition, in the high-performance region, the supply of 4 kg of working fluid at a speed of 1.0 kg/s can also be considered the best solution, and R404a is the most suitable working fluids for thermal energy storage. Under Europe Transient Cycle (ETC), the average temperature, availability, satisfaction, and CI are increased by 2.9%, 7.46%, 34.1%, and 100%, respectively, with the TES system, and the standard deviation is decreased by 53%. Compared to the ORC system, the coupled ORC-TES system leads to an increase in exhaust back pressure (EBP), but does not lead to an increase in fuel consumption due to the improved thermal efficiency of the ORC system. In addition, the integrated ORC-TES system can improve the SCR catalytic efficiency and reduce NOx emissions. From a cost-benefit analysis, the ORC-TES system is practically feasible.