Hydrogen Engine Exhaust Aftertreatment - 2022

Since 2021, we have been conducting intensive research at ITnA on the exhaust gas aftertreatment (AGN) of hydrogen engines. Since the H2 engine is basically CO2-free, the elimination of the remaining pollutant emissions makes it a zero-impact engine. These are mainly nitrogen oxides, since the H2 engine is preferably operated with lean combustion. For this reason, AGN is also strongly oriented towards the diesel engine. We conducted our research mainly on the test bench, on passenger car and commercial vehicle engines.

It has been shown that selective catalytic reduction (SCR) with ammonia (NH3) as the reducing agent also works excellently on the hydrogen engine. The conversion rates correspond to those known from the diesel engine. In some cases, the unburned hydrogen present in the exhaust gas can inhibit the SCR reaction. However, this is not evident in all SCR technologies; apart from this, the oxidation of H2 itself is easy. In fact, hydrogen is a very reactive element that can be easily oxidized over platinum. It was shown that smaller and less loaded oxidation catalysts (than those used in diesel engines) are sufficient to convert H2 even at low temperatures.

Since early 2022, we have focused our investigations on transient cycles. We are looking at both the WLTC, WLTP and NRTC statutory cycles (for cars, trucks and non-road) as well as aggressive and passive RDE surrogate cycles. A prerequisite for the investigations was the successful development of a control unit for the transient operation of quality-controlled H2 engines with direct injection at ITnA.

The investigations to date show that the H2 engine in transient operation already achieves a lower level of raw nitrogen oxide emissions than the diesel engine. For example, raw NOx of < 100 mg/km can be achieved in WLTC for a common engine, which is already within the range of the currently valid EU6d limit. Due to the typical NOx characteristics of the H2 engine, there is a stronger dependence of the emissions on the dynamics of the driving cycle than with the diesel engine.

By means of an exhaust gas aftertreatment consisting of oxidation catalyst and NH3-SCR, these already low raw emissions can be converted to very low values. In the cold-started WLTC, emissions of less than 10 mg/km could be demonstrated (see HyDISI). Using an electric heating catalyst, even values below 2 mg/km are feasible. In these investigations, we benefit from our experience with AGN of diesel engines, for example from the RC-LowCAP project.

Publications

Schutting, Eberhard ; Roiser, Sebastian Gerhard ; Eichlseder, Helmut et al / Hydrogen Engine Exhaust Aftertreatment. 43rd International Vienna Motor Symposium 2022. vol. 2 Austrian Association for Automotive Engineering, 2022.

Roiser, Sebastian Gerhard ; Christoforetti, Paul ; Schutting, Eberhard et al. / Emission Behavior and Aftertreatment of Stationary and Transient Operated Hydrogen Engines. Proceedings -Thiesel 2022 Conference on Thermo- and Fluid Dynamics of Clean Propulsion Powerplants. 2022. pp. 178-194