Combustion Engine Waste Heat Recovery Research Articles

Review of Organic Rankine Cycles for Internal Combustion Engine Waste Heat Recovery: Latest Decade in Review

The last decade (2013–2023) was the most prolific period of organic Rankine cycle (ORC) research in history in terms of both publications and citations. This article provides a detailed review of the broad and voluminous collection of recent internal combustion engine (ICE) waste heat recovery (WHR) studies, serving as a necessary follow-on to the author’s 2013 review. Research efforts have targeted diverse applications (e.g., vehicular, stationary, and building-based), and it spans the full gamut of engine sizes and fuels. Furthermore, cycle configurations extend far beyond basic ORC and regenerative ORC, particularly with supercritical, trilateral, and multi-loop ORCs. Significant attention has been garnered by fourth-generation refrigerants like HFOs (hydrofluoroolefins), HFEs (hydrofluoroethers), natural refrigerants, and zeotropic mixtures, as research has migrated away from the popular HFC-245fa (hydrofluorocarbon). Performance-wise, the period was marked by a growing recognition of the diminished performance of physical systems under dynamic source conditions, especially compared to steady-state simulations. Through advancements in system control, especially using improved model predictive controllers, dynamics-based losses have been significantly reduced. Regarding practically minded investigations, research efforts have ameliorated working fluid flammability risks, limited thermal degradation, and pursued cost savings. State-of-the-art system designs and operational targets have emerged through increasingly sophisticated optimization efforts, with some studies leveraging “big data” and artificial intelligence. Major programs like SuperTruck II have further established the ongoing challenges of simultaneously meeting cost, size, and performance goals; however, off-the-shelf organic Rankine cycle systems are available today for engine waste heat recovery, signaling initial market penetration. Continuing forward, next-generation engines can be designed specifically as topping cycles for an organic Rankine (bottoming) cycle, with both power sources integrated into advanced hybrid drivetrains.

Thermodynamic Performance Analyses and Optimization of Dual-Loop Organic Rankine Cycles for Internal Combustion Engine Waste Heat Recovery

Waste heats of an internal combustion engine (ICE) are recovered by a dual-loop organic Rankine cycle (DORC). Thermodynamic performance analyses and optimizations are conducted with 523.15–623.15 K exhaust gas temperature (Tg1). Cyclopentane, cyclohexane, benzene, and toluene are selected as working fluids for high-temperature loop (HTL), whereas R1234ze(E), R600a, R245fa, and R601a are selected as working fluids for low-temperature loop (LTL). The HTL evaporation temperature, condensation temperature, and superheat degree are optimized through a genetic algorithm, and net power output is selected as the objective function. Influences of Tg1 on system net power output, thermal efficiency, exergy efficiency, HTL evaporation temperature, HTL condensation temperature, HTL superheat degree, exhaust gas temperature at the exit of the HTL evaporator, heat utilization ratio, and exergy destruction rate of the components are analyzed. Results are presented as follows: the net power output is mainly influenced by HTL working fluid. The optimal LTL working fluid is R1234ze(E). The optimal HTL evaporator temperature increases with Tg1 until it reaches the upper limit. The optimal HTL condensation temperature increases initially and later remains unchanged for a cyclopentane system, thus keeping constant for other systems. Saturated cycle is suitable for cyclohexane, benzene, and toluene systems. Superheat cycle improves the net power output for a cyclopentane system when Tg1 is 568.15–623.15 K.

Internal combustion engine waste heat recovery by a thermoelectric generator inserted at combustion chamber walls

Internal combustion engine waste heat recovery by a thermoelectric generator inserted at combustion chamber walls

Thermodynamic analysis of dual-loop organic Rankine cycle using zeotropic mixtures for internal combustion engine waste heat recovery

The dual-loop organic Rankine cycle (DORC) is a promising technology for internal combustion engine waste heat recovery. Zeotropic mixtures can improve temperature matches with heat source and sink in the phase change process for its non-isothermal phase change characteristic. Thus, zeotropic mixtures are adopted for high-temperature loop (HTL) and low-temperature loop (LTL) of DORC. Cyclopentane/cyclohexane and benzene/toluene mixtures are used for HTL, whereas isobutane/isopentane (R600a/R601a) mixtures are selected as working fluids for LTL. The mole fraction effects of mixtures on net power output, exergy efficiency, exergy destruction rate (HTL evaporator, condenser/evaporator, LTL preheater, and condenser), and heat utilization ratio of waste heat are analyzed. The influences of engine exhaust gas temperature on net power output and exergy destruction rate are also discussed. Results show that the use of mixtures for the two loops can reduce the exergy destruction rate of HTL evaporator and LTL condenser compared to that of pure working fluids system and the exergy destruction rate of condenser/evaporator compared to that of mixtures using only one loop system. Furthermore, these mixtures increase the heat utilization ratio of waste heat, net power output, and exergy efficiency compared to those of a pure working fluid system. When cyclopentane/cyclohexane or benzene/toluene mixtures are used for HTL and R600a/R601a mixtures are used for LTL, the system net power output relative increment rates of mixture systems are 2.5–9.0% and 1.4–4.3%, respectively, compared to those of corresponding pure working fluids system with 573.15–623.15 K engine exhaust gas temperature.

A Combined Organic Rankine Cycle With Double Modes Used for Internal Combustion Engine Waste Heat Recovery

A combined organic Rankine cycle (ORC) was proposed for both engine coolant energy recovery (CER) and exhaust energy recovery (EER), and it was applied to a gasoline direct injection (GDI) engine to verify its waste heat recovery (WHR) potential. After several kinds of organic working medium were compared, R123 was selected as the working fluid of this ORC. Two cycle modes, low-temperature cycle and high-temperature cycle, were designed according to the evaporation way of working fluid. The working fluid is evaporated by coolant heat in low-temperature cycle but by exhaust heat in high-temperature cycle. The influence factors of cycle performance and recovery potential of engine waste heat energy were investigated by cycle simulation and parametric analysis. The results show that recovery efficiency of waste heat energy is influenced by both engine operating conditions and cycle parameters. At 2000 r/min, the maximum recovery efficiency of waste heat energy is 7.3% under 0.2 MPa brake mean effective pressure (BMEP) but 10.7% under 1.4 MPa BMEP. With the combined ORC employed, the fuel efficiency improvement of engine comes up to 4.7% points under the operations of 2000 r/min and 0.2 MPa BMEP, while it further increases to 5.8% points under the operations of 2000 r/min and 1.4 MPa BMEP. All these indicate that the combined ORC is suitable for internal combustion (IC) engine WHR.

A Commander–Tracker–Executor based energy management framework for an engine waste heat recovery system

Energy management for an internal combustion engine waste heat recovery system presents a complex problem. There are the coupling issues of energy recovery and energy utilization. In addition, there are the problems arising from the large thermal inertia of the energy network. A Commander–Tracker–Executor energy manager framework is proposed as the management solution. Under this approach the Commander is designed to optimally split the engine’s exhaust energy among the different energy devices of the energy network at the lowest fuel cost. A disturbance estimation-based receding horizon controller is designed as a Tracker to follow the Commander’s commands in real time. The Commander’s decisions are made in real time based on each energy device’s efficiency model, the torque demand given by the driver, and the corresponding heat rejection requirement of the whole system. The Tracker works as a trajectory follower to transform the Commander’s decisions into the actuators’ control objectives. The Executor ensures that the energy management goals are achieved in line with the actuators’ control objectives. An energy network constructed of <Engine>- <Power Turbine>- <Organic Rankine Cycle System>- <Electric Cooling system>- <Battery>- <Integrated starter and Generator> has been taken as an example for the simulation study. The simulation results indicate that: the manager exhibited fairly good fuel-saving potentiality along a whole driving cycle; the proposed Commander showed effective exhaust energy splitting performance; and the Tracker scheme demonstrated good tracking capability and robustness.

Technology competition in the internal combustion engine waste heat recovery: a patent landscape analysis

Fuel prices and tightening emission standards have challenged the dominance of internal combustion engines. As a response to this changed business context, the automotive industry has shown active interest in waste heat recovery technologies, which have seen rapid development in recent years. This paper uses a literature review and patent landscape analysis to study key emerging technologies in the field, namely, thermoelectric generators, and Rankine cycle and organic Rankine cycle systems. The state-of-the-art review highlights the challenges, advantages and future prospects of the selected technologies. The patent analysis reveals the leading countries, principal technological development indicators and most important actors active in the field. The results indicate a growing trend of patenting in all selected technologies. The United States and Japan are by far the most dominant countries in the waste heat recovery area, although their relative share of patent applications is declining. By applying a patent landscape approach, the study offers a quantitative perspective on current developments in waste heat recovery technology, provides indicators of future trends, and contributes to debate about technological competition in the automotive industry. Based on the conducted analyses, thermoelectric generators seems to be the most developed of the alternatives and closest to commercial application. Rankine cycle-based technologies, although less well developed, potentially offer greater environmental gains and better efficiency than thermoelectric generators. The study provides valuable information for stakeholders interested in waste heat recovery technologies and gives policymakers perspectives regarding different technological options in development of cleaner engine solutions.