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.

Engine manufacturers are considering the implementation of thermodynamic cycles for Waste Heat Recovery (WHR) in order to increase Internal Combustion Engine (ICE) system thermal efficiency. For these secondary cycles, the literature illustrates the preference of Organic Rankine Cycles (ORC's) due to its simplicity and efficient recovery of the medium grade waste heat found in engine exhaust. This paper simulates the heat recovery capacity of eight dry fluids (butane, pentane, hexane, cyclopentane, benzene, toluene, R245fa, and R123) for an ORC based on the exhaust from a single-cylinder diesel engine-generator operating under five different loading conditions. The model, developed using REFPROP and the Matlab Optimization Toolbox, represents the physical components using isentropic pump and expander efficiencies, along with two-zone heat exchangers. All fluids present cycle efficiencies between 10-15%, with the heaviest hydrocarbons generating the largest amount of work. Of these fluids, pentane is the ideal candidate for an ORC. This fluid illustrates an approximate 10% improvement to the engine-generator efficiency across all conditions. Moreover, the simulation predicts low peak pressures and expansion ratios that are compatible with available displacement expanders. In addition, this effort compares evaporator flow configurations (counter vs. parallel), along with condenser air flow rates. For the evaporator, results illustrate that a parallel flow evaporator arrangement can transfer more heat in phase change applications by setting the high temperature difference in the area of low heat transfer coefficients. Different air flow rates across the condenser show little variation in cycle efficiency with the consumption of fan power at high rates reducing the overall power generated.

Researchers developing pervious pavements over the past few decades have commendably demonstrated long-term run-off reduction using a diverse collection of materials. Today, pervious pavements are widely recognized as a low impact development technique and a type of green infrastructure, and installations are proliferating throughout the United States and worldwide. The entire field of pervious pavements though, is being profoundly stunted by three persistent problems: conflicting nomenclature, flawed testing standards, and the absence of a holistic green design framework. This study examines each problem and proposes novel solutions. On nomenclature, a multi-channeled study of the terms “pervious”, “permeable”, and “porous” considers each word’s etymology and usage in the academic literature, in ASTM International standards, and by (U.S.-based) governmental entities. Support is found for using pervious pavements (i.e., “through” the “road”) as the over-arching category of all water passable pavements, branching down into porous pavements (i.e., “full of pores”, including porous asphalt and porous concrete) and permeable pavements (i.e., “containing passages”, often between paver units). ASTM International standards are shown to insufficiently account for the impact of paver unit size on infiltration rate, warranting the development of a more reliable testing method featuring variable infiltration ring size, shape, and placement. Finally, a ten-part holistic green design framework is elucidated for use in assessing candidate pavements and engineering new pavements, contextualizing the latest pervious pavement research and illuminating a brighter path forward.

This survey examines how mechanical engineers are being prepared to be responsible stewards of the environment by offering a multi-channeled look at a diverse collection of twelve US colleges and universities, with connections to the larger global context. This study enumerates the external influences of professional organizations, those responsible for program accreditation (Accreditation Board for Engineering and Technology (ABET)), professional conduct (American Society of Mechanical Engineers), and licensure (National Council of Examiners for Engineering and Surveying, National Society of Professional Engineers). At the curricular level, this study presents current mechanical engineering curricula via core courses (required at most institutions) and non-core courses (required at a minority of institutions or elective courses). The curriculum study identifies fifteen core courses and uses the Open Syllabus Project and online bookstores to identify a representative textbook and classify the environmental content therein. Immediate results show the environment receiving sparse treatment in core course textbooks, institutions having zero environment-focused degree requirements, and a tendency towards offering electives that are narrowly focused on green technologies. Elective offerings mirror ABET’s recent move away from emphasizing the “broad education necessary to understand the impact” of engineering solutions to instead “consider the impact of” engineering solutions in an environmental context. Overall, the environmental education mechanical engineers are receiving is insufficient in amount and lacking in scientific and ethical foundation. Ideally, every mechanical engineering program should include coordinated environmental content throughout the curriculum and require at least one course that teaches both environmental design principles and the importance of environmental stewardship. A novel approach eschews the typical artes mechanicae course structure to teach environmental stewardship in the artes liberales educational tradition, emphasizing multi-dimensional thinking by employing great books style discussions of seminal scientific, ethical, and technological works.