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The H2ICE project aims at the development of an innovative hybrid powertrain for urban buses, based on a hydrogen fueled Internal Combustion Engine (ICE), capable of providing a zero CO2 and near zero criteria pollutant emissions solution, with a significant cost saving (up to one order of magnitude at time of writing) if compared with other zero emissions powertrains, such as Fuel Cell Electric Vehicles (FCEVs). The project will focus on the development of a new generation of hydrogen fueled ICEs, designed to be operated with ultra-lean mixtures, thus achieving extremely low NOx emissions (below 0.05 g/kWh), along with unprecedented efficiency values (above 42%). These figures make these new engines extremely promising candidates for urban buses applications, for which a quite limited range is typically requested, and tank refueling is not an issue, since it is possible for captive fleets to centralize the fuel stations in a single hub. Moreover, these already outstanding efficiency values could be further enhanced by the synergic combination with hybrid propulsion technologies, that are particularly suitable for urban buses applications, for which series hybrid could significantly benefit from energy recovery through regenerative braking, as well as from a substantial downsizing of the ICE, since vehicle acceleration performance can be decoupled from engine power output. However, the full exploitation of the potential of such a hybrid powertrain requires a substantial enhancement of the state of the art, since several challenging issues have to be addressed. In particular, the control of the fuel injection and of the combustion process is extremely challenging, due to the high risk of backfire in case of port fuel injection and to the complexity of managing mixture formation through the supersonic flow of the gaseous fuel in case of direct injection, as well as to the need of identifying a “sweet spot” in the ultra-lean combustion region which could allow extremely low NOx emissions along with high combustion efficiencies. Specifically designed combustion diagnostic techniques will therefore be developed, for knock and misfire detection. Moreover, to further enhance the engine efficiency, different Waste Heat Recovery (WHR) systems will be carefully scrutinized, including both Organic Rankine Cycle (ORC)-based recovery units as well as electric turbo-compounding. Finally, a Selective Catalytic Reduction (SCR) aftertreatment system will be developed to bring already low engine-out NOx to near-zero emissions levels. At powertrain level, advanced energy management strategies, fully exploiting V2X communication, will be developed. In conclusion the performance of the whole hybrid hydrogen fueled propulsion system will be assessed on a virtual test rig over several Real Driving Emission (RDE) tests, targeting to achieve a hydrogen fuel consumption of about 0.1 kg/km, which can successfully compete with a FCEV at a much lower cost.