Assessment of Waste Heat Recovery Options in Passenger Car Applications by Various Rankine Cycles

Abstract

In power plant applications it is state of the art to recover waste heat in combined-cycle power plants. Hence, overall efficiencies are increased from 35% to more than 45%. Actually, in marine applications as well as in commercial vehicle applications, similar technologies are developed to recover waste heat. The common basis of all these applications is running only or mostly at steady-state conditions. With passenger cars the operation conditions are completely different, as passenger cars are operated under highly transient conditions. In the work presented, the characteristics of a passenger car-based internal combustion engine are analyzed. From exhaust gas temperatures and exhaust gas mass flows, the characteristic of available waste heat over load and speed is estimated. Based on this characteristic an ideal, a water-based Rankine cycle is designed and compared with different organic Rankine cycles. Finally, the expected waste heat recovery at typical passenger car operation conditions is determined by weighting the waste heat recovery characteristics with the operation conditions of the new European driving cycle (NEDC). Based on NEDC scenario, only about 0.2 kW of power could be recovered. By moving toward range extender conditions, between 2.5 and 4.0 kW would be recoverable.

Assessing fuel consumption reduction in Revercycle, a reversible mobile air conditioning/ Organic Rankine Cycle system

“…The net recovered mechanical power in ORC mode is 0.98 kW. (Heidrich and Krisch, 2014) underlined that evaluating the fuel economy of an ORC on the design point is only half the truth. In real life operation the ORC system will experience transient operation conditions.…”

Simulation analysis of cooling methods of an on-board organic Rankine cycle exhaust heat recovery system

“…The thermal efficiency of engines is approximately 40% . Approximately 30% of the energy input from fuel is contained in the exhaust gas, and the rest of heat energy is released through intake air intercooling and engine coolant. Recovering the exhaust heat is an effective method for achieving the reduction in fuel consumption and emissions .…”

“…New vehicular emission regulations has been introduced in 2014, 1 and the regulations have been implemented for light duty diesel vehicles at ambient temperature of 293 K to 303 K. 2 The thermal efficiency of engines is approximately 40%. 3 Approximately 30% of the energy input from fuel is contained in the exhaust gas, 4 and the rest of heat energy is released through intake air intercooling and engine coolant. Recovering the exhaust heat is an effective method for achieving the reduction in fuel consumption and emissions.…”

Study of particulate matter and gaseous emissions in gasoline direct injection engine using on-board exhaust gas fuel reforming

“…Despite the technical advances in the automotive sector, still between 20-40% of fuel energy is wasted in the engine exhaust [14,15] with a 6% exergy content available [16]. With the aim of improving overall engine's efficiency, different techniques for exhaust energy recovery have been extensively researched in the literature such as thermoelectrical generators [17,18] and Rankine cycles [19,20]. In addition to thermal recovery, catalytic techniques offer the possibility of utilizing products from engine combustion, water and CO 2 .…”

“…In addition, the presence of H 2 promotes the formation of OH radicals, which reduces the soot formation rate [17] and enhances soot oxidation [18]. Hydrogen combustion could also raise the in-cylinder temperature, which can enhance PM oxidation [18] but at the same time can increase NOx emissions [19,20]. Despite these benefits, safety reasons due to abnormal hydrogen combustion (e.g.…”