Stoichiometric H2ICE with water injection and exhaust and coolant heat recovery through organic Rankine cycles

High power density, stoichiometric, turbocharged, directly injected engines with water injection and a three way catalytic converter after treatment have been proposed as one of the most promising H2ICE [1]. These throttle controlled engines have top brake efficiencies exceeding 40%, but large penalties in efficiency reducing the load with 1 bar BMEP values approaching 10%. Recovery of the large amount of fuel energy lost in the coolant especially at low loads as well as the fuel energy lost in the exhaust that is significant at high loads and speeds may push not only the top brake efficiencies to exceed the 45% mark, but also to dramatically increase the low load efficiency compromised by the throttling. In this paper, recovery of the waste heat from the exhaust gases and the coolant in a H2ICE is performed with Organic Rankine Cycles (ORC). The engine without ORC has a maximum efficiency of 42% and an average efficiency over the map points of 32.7%. With the exhaust ORC, neglecting the possible back pressure increase due to the heat exchanger downstream of the catalytic converter the maximum efficiency increases to 45.6%, and the average efficiency rises to 35.3%. With the coolant ORC, neglecting the reduced mechanical efficiency for the coolant back pressure increment, the maximum efficiency increases to 43.4% and the average efficiency increases to 34.6%. Finally, combining the two ORC with same assumptions, the maximum efficiency increases to 46.9% and the average efficiency to 38%.

► ORC may be used in stoichiometric H2ICE to increase efficiency over the full load range. ► The exhaust ORC increases the maximum efficiency of 3.6% and the average efficiency of 2.6%. ► The coolant ORC increases the maximum efficiency of 1.4% and the average efficiency of 1.9%. ► Combining the two ORC the maximum efficiency increases of 4.9% and the average of 5.3%.