Waste Energy Recovery and Valorization in Internal Combustion Engines for Transportation

Abstract

Internal Combustion Engines (ICE) are experiencing a transition era in which research and innovation are mainly pushed by environmental issues: emission reduction and fuel saving are indispensable requirements of the new technologies, otherwise the end of ICE is proposed in Europe. Modifications, in reality, are under discussion by 2026 but the environmental issues are anyway welcomed. In the transportation sector, today dominated by ICEs, it appears that the reduction in the propulsion power, hybridization at various degrees, and exhaust post-treatment improvements will guarantee technological solutions able to support the transition in the next couple of decades toward full electric propulsion. Waste Heat Recovery (WHR) is a very interesting opportunity since almost two-thirds of fuel energy is not converted into mechanically useful energy. Moreover, the integration with other thermal streams on board (cooling and lubricating mediums, EGR cooling) can add further value to the recovery opportunity as well as the concept of managing the engine thermal management which can produce a sensible contribution that is appreciated mainly during urban driving. A huge scientific effort is underway, and a great expectation is perceptible. More generally, the technological options that can achieve a reduction in overall fuel consumption and, thus, the improvement of global engine efficiency, are the most valuable when they can be introduced without massive changes to the engine layout. This happens in all the energy applications in which ICEs are involved since the recovery unit can be introduced in the exhaust line. The mechanical energy recovered can be easily transformed into electrical energy, so represents an interesting integration with the hybrid propulsion powertrains. In this paper, a review of the most important technologies referred to the WHR is presented, outlining advantages and drawbacks, and setting up the presently available technologies referred to the transportation sector.

A New Generation of Hydrogen-Fueled Hybrid Propulsion Systems for the Urban Mobility of the Future

“…Figure 11 shows the resulting values, which range from 10 to 25 bar, almost linearly with the exhaust temperature. It is just a point to notice that the maximum pressure achieved is not so far from the critical point of the R245fa fluid and also represents a technical limitation for safety and technology of the components and materials [57].…”

“…Figure 11 shows the resulting values, which range from 10 to 25 bar, almost linearly with the exhaust temperature. It is just a point to notice that the maximum pressure achieved is not so far from the critical point of the R245fa fluid and also represents a technical limitation for safety and technology of the components and materials [57]. The evaporating pressure is also the parameter that sets the ORC efficiency since the condensing pressure is almost fixed at the value of 4 bar, related to the environmental conditions of the cold sink onboard.…”

Energy Analysis of Waste Heat Recovery Using Supercritical CO2 Brayton Cycle for Series Hybrid Electric Vehicles

“…The average frequency of stops and starts is (60-70) stop/h, with an average duration of (15-50) min, which represents an average downtime of (25-40)% [12]. Thus, the fuel consumption of Diesel hybrid vehicles can be lower by about (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)% than that of conventional standard Diesel vehicles [13].…”

Turbocompound energy recovery option on a turbocharged diesel engine

“…Heavy-duty vehicles would particularly benefit from these recovery units since emission consumption reduction is more significantly associated with the reduction of transport costs [10,11]. WHR units can be divided into direct and indirect, depending if the working fluid producing power is the exhaust gas itself or a secondary fluid that is thermally coupled to the exhaust gas [12].…”