Influence of exhaust backpressure on the performance of port-fuel-injected large-bore hydrogen engines with different turbocharger configurations

Abstract

The transition of large-bore internal combustion engines to hydrogen offers a pathway for decarbonizing stationary power generation. However, achieving competitive power densities with port fuel injection requires high charging pressures due to intake air displacement and lean-burn combustion. The combination of high charging requirements and low exhaust gas enthalpies constrains conventional single-stage turbocharging, necessitating alternative concepts such as multi-stage or assisted systems. Because the charging architecture directly influences in-cylinder thermodynamics, this study experimentally quantifies the impacts of exhaust backpressure on a single-cylinder large-bore hydrogen engine by comparing an unrestricted exhaust baseline with configurations emulating the backpressure of single-stage and assisted turbocharging concepts. Results indicate that applying a realistic single-stage turbocharger efficiency decreases the indicated engine efficiency by 3.7 percentage points compared to an unrestricted baseline. Emulating an electrically or mechanically assisted turbocharger setup restricted the stable operating map, reduced the maximum indicated mean effective pressure from 19.7 to 18.7 bar, and caused an indicated efficiency penalty of up to 3.1 percentage points. This highlights the fundamental trade-off: achieving the necessary boost pressure either induces a thermodynamic penalty via high exhaust backpressure or requires additional power to drive the compressor. Regarding emissions, the elevated backpressure substantially reduces nitrogen oxides at medium loads with less lean mixtures compared to the unrestricted baseline due to the increased trapping of residual gas, while causing a slight increase at low loads. At high engine loads, however, both nitrogen oxides and unburned hydrogen emissions remain unaffected by the increased backpressure. These findings demonstrate the necessity of advanced charging architectures, such as multi-stage or externally assisted systems, to optimize the efficiency of stationary hydrogen engines.