Carbon-free internal combustion engine fueled by hydrogen and hydrogen-carrier fuels

The stringent international policies governing the future rise in global temperature trigger the need for sustainable clean energy sources that meet the demands for quality of life and economic growth, while avoiding emitting greenhouse gases (such as carbon dioxide) into the atmosphere. Hydrogen (H2) can help tackling various critical energy challenges, including the mobility sector. The use of H2 as an energy carrier in mobility applications is, thus, expected to increase significantly in the foreseeable future. One of the challenges associated with the use of H2 is its low density in gaseous form, which makes it challenging to store and transport it effectively in large quantities. Ammonia (NH3) is a feasible H2-carrier, as NH3 can be stored and transported in liquid form if pressurized to 11 bar only. Compared to H2, however, NH3 has significantly inferior combustion characteristics, in terms of the flame speed and heating value. NH3 thus needs to be cracked to blends of hydrogen and nitrogen (H2/N2) to release the H2 prior to combustion. The combustion application can be fueled by an H2/N2 blend or pure H2, depending on the design and characteristics of combustion system. Fueling mobile transport applications with NH3 thus calls for designing an onboard cracking system; this project aims at developing novel catalyst materials for onboard NH3 cracking, targeting the reduction of the activation energy and temperature needed for cracking, while increasing the H2/N2 throughput and adapting to the variable load conditions of the vehicle engine. Hydrogen has challenging combustion characteristics, especially if used as fuel in existing internal combustion engines (ICEs). Some of these challenges include low ignition energy, which increases the risks of flashback and premature ignition (despite the advantage of enabling lean operation), as well as small quenching distance, which increases the thermal stresses on combustion-chamber walls. The low density of H2 also makes it displace air inside the intake manifold and/or cylinders of the engine, which reduces the power output. Furthermore, H2 combustion occurs at higher temperature, compared to hydrocarbon fuels at the same equivalence ratio, which promotes NOx formation. Having an ICE optimized for H2 operation at one given set of operating conditions is not difficult, but smooth operation over a range of conditions is the challenge. In this project, an ICE will be retrofitted to run effectively and safely on different blends of H2/N2 as well as pure H2. Experiments will be performed trying to find solutions to overcome the challenges associated with H2 combustion in ICEs and also to evaluate the engine performance, emissions (NOx), operability, and safety. Thermal efficiency and power output will be evaluated for different H2/N2 blends and for pure H2 over wide ranges of engine load and equivalence ratio. All data will be compared to the baseline case of natural-gas (CH4) fuel. Detailed numerical simulations will also be performed to characterize the combustion process in detail.