Dual-loop Organic Rankine Cycle System Research Articles

Parametric analysis of a dual loop Organic Rankine Cycle (ORC) system for engine waste heat recovery

This paper presents a dual loop Organic Rankine Cycle (ORC) system consisting of a high temperature (HT) loop and a low temperature (LT) loop for engine waste heat recovery. The HT loop recovers the waste heat of the engine exhaust gas, and the LT loop recovers that of the jacket cooling water in addition to the residual heat of the HT loop. The two loops are coupled via a shared heat exchanger, which means that the condenser of the HT loop is the evaporator of the LT loop as well. Cyclohexane, benzene and toluene are selected as the working fluids of the HT loop. Different condensation temperatures of the HT loop are set to maintain the condensation pressure slightly higher than the atmosphere pressure. R123, R236fa and R245fa are chosen for the LT loop. Parametric analysis is conducted to evaluate the influence of the HT loop condensation temperature and the residual heat load on the LT loop. The simulation results reveal that under different condensation conditions of the HT loop, the pinch point of the LT loop appears at different locations, resulting in different evaporation temperatures and other thermal parameters. With cyclohexane for the HT loop and R245fa for the LT loop, the maximum net power output of the dual loop ORC system reaches 111.2kW. Since the original power output of the engine is 996kW, the additional power generated by the dual loop ORC system can increase the engine power by 11.2%.

Performance analysis of a dual-loop organic Rankine cycle (ORC) system with wet steam expansion for engine waste heat recovery

A dual-loop organic Rankine cycle (ORC) system is designed to recover the waste heat of a diesel engine. The high-temperature (HT) loop utilizes the heat load of the engine exhaust gas, and the low-temperature (LT) loop uses the heat load of the jacket cooling water and the residual heat of the HT loop sequentially. These two loops are coupled via a shared heat exchanger. Water is selected as the working fluid for the HT loop and wet steam expansion, which can be implemented through screw expanders, is exploited. The dryness fraction of the wet steam at the inlet of the expander can be adjusted to attain a suitable evaporation temperature and provide a better temperature match with the heat source. The working fluid candidates for the LT loop are chosen to be R123, R236fa and R245fa. The influence of the HT loop parameters on the performance of the LT loop is evaluated. The simulation results reveal that under different operating conditions of the HT loop, the pinch point of the LT loop occurs at different locations and therefore, results in different evaporation temperatures and other thermal parameters. The maximum net power output of the dual-loop ORC system reaches 115.1kW, which leads to an increase of 11.6% on the original power output of the diesel engine.

Analyzing the Performance of a Dual Loop Organic Rankine Cycle System for Waste Heat Recovery of a Heavy-Duty Compressed Natural Gas Engine

A dual loop organic Rankine cycle (DORC) system is designed to recover waste heat from a heavy-duty compressed natural gas engine (CNGE), and the performance of the DORC–CNGE combined system is simulated and discussed. The DORC system includes high-temperature (HT) and low-temperature (LT) cycles. The HT cycle recovers energy from the exhaust gas emitted by the engine, whereas the LT cycle recovers energy from intake air, engine coolant, and the HT cycle working fluid in the preheater. The mathematical model of the system is established based on the first and second laws of thermodynamics. The characteristics of waste heat energy from the CNGE are calculated according to engine test data under various operating conditions. Moreover, the performance of the DORC–CNGE combined system is simulated and analyzed using R245fa as the working fluid. Results show that the maximum net power output and the maximum thermal efficiency of the DORC system are 29.37 kW and 10.81%, respectively, under the rated power output condition of the engine. Compared with the original CNG engine, the maximum power output increase ratio and the maximum brake specific fuel consumption improvement ratio are 33.73% and 25%, respectively, in the DORC–CNGE combined system.

Parametric analysis of a dual-loop ORC system for waste heat recovery of a diesel engine

The maximum potential of a dual-loop organic Rankine cycle (ORC) applied to a light-duty diesel engine is analyzed over the engine's operational range by developing a mathematical model based on physical processes and boundary conditions specified according to measured data from an engine test. We further evaluate the effects of three working parameters—expander isentropic efficiency, evaporation pressure of the high-temperature loop, and condensation temperature of the low-temperature loop—on the performance of the dual-loop ORC system. The results show that using the proposed dual-loop ORC system improves the net power output of a diesel automotive engine by 19–22% in the peak thermal-efficiency region under allowable working conditions of the engine, and by 53–72% in the high-speed and low-load regions. Over the engine's entire operational range, the effective thermal efficiency increases by a maximum of 8%. Moreover, the expander isentropic efficiency and the condensation temperature of the low-temperature loop are two critical parameters that affect combined system performance.

Performance analysis of waste heat recovery with a dual loop organic Rankine cycle (ORC) system for diesel engine under various operating conditions

To take full advantage of the waste heat from a diesel engine, a set of dual loop organic Rankine cycle (ORC) system is designed to recover exhaust energy, waste heat from the coolant system, and released heat from turbocharged air in the intercooler of a six-cylinder diesel engine. The dual loop ORC system consists of a high temperature loop ORC system and a low temperature loop ORC system. R245fa is selected as the working fluid for both loops. Through the engine test, based on the first and second laws of thermodynamics, the performance of the dual loop ORC system for waste heat recovery is discussed based on the analysis of its waste heat characteristics under engine various operating conditions. Subsequently, the diesel engine-dual loop ORC combined system is presented, and the effective thermal efficiency and the brake specific fuel consumption (BSFC) are chosen to evaluate the operating performances of the diesel engine-dual loop ORC combined system. The results show that, the maximum waste heat recovery efficiency (WHRE) of the dual loop ORC system can reach 5.4% under engine various operating conditions. At the engine rated condition, the dual loop ORC system achieves the largest net power output at 27.85kW. Compared with the diesel engine, the thermal efficiency of the combined system can be increased by 13%. When the diesel engine is operating at the high load region, the BSFC can be reduced by a maximum 4%.

Performance comparison and working fluid analysis of subcritical and transcritical dual-loop organic Rankine cycle (DORC) used in engine waste heat recovery

In this paper, a new dual-loop organic Rankine cycle (DORC) consisting of a high-temperature (HT) cycle and a low-temperature (LT) cycle is proposed to recover the waste heat of the exhaust and the engine coolant and the residual heat of the HT cycle. Two different systems are adopted. According to the cycle mode adopted in the LT cycle, the system can be defined as subcritical–subcritical (sub–sub) DORC or subcritical–transcritical (sub–trans) DORC. R125, R143a and R218 are chosen as the candidate working fluids in the LT cycle of the sub–trans DORC, while R124, R134a, R245fa, R600, R600a and R1234yf are the candidates of the sub–sub DORC. Net output power and exergy efficiency are selected as the objective functions. Results show that R143a-based sub–trans DORC system performs the best and the net output power and the exergy efficiency are 39.91kW and 48.42%, respectively. Small condensation temperature of the HT cycle is advantageous for the performance optimization. Irreversibilities of evaporator EHT, condenser CLT and the two turbines (THT and TLT) are the top four, which are the optimization objectives. For R143a-based sub–trans DORC, system performs best with 100% operating load.

The national advisory committee for aeronautics

In this study, a dual loop ORC (organic Rankine cycle) system is adopted to recover exhaust energy, waste heat from the coolant system, and intercooler heat rejection of a six-cylinder CNG (compressed natural gas) engine. The thermodynamic, heat transfer, and optimization models for the dual loop ORC system are established. On the basis of the waste heat characteristics of the CNG engine over the whole operating range, a GA (genetic algorithm) is used to solve the Pareto solution for the thermodynamic and heat transfer performances to maximize net power output and minimize heat transfer area. Combined with optimization results, the optimal parameter regions of the dual loop ORC system are determined under various operating conditions. Then, the variation in the heat transfer area with the operating conditions of the CNG engine is analyzed. The results show that the optimal evaporation pressure and superheat degree of the HT (high temperature) cycle are mainly influenced by the operating conditions of the CNG engine. The optimal evaporation pressure and superheat degree of the HT cycle over the whole operating range are within 2.5–2.9 MPa and 0.43–12.35 K, respectively. The optimal condensation temperature of the HT cycle, evaporation and condensation temperatures of the LT (low temperature) cycle, and exhaust temperature at the outlet of evaporator 1 are kept nearly constant under various operating conditions of the CNG engine. The thermal efficiency of the dual loop ORC system is within the range of 8.79%–10.17%. The dual loop ORC system achieves the maximum net power output of 23.62 kW under the engine rated condition. In addition, the operating conditions of the CNG engine and the operating parameters of the dual loop ORC system significantly influence the heat transfer areas for each heat exchanger.