High Efficiency HD Hydrogen Combustion Engines: Improvement Potentials for Future Regulations 2022-01-0477

Hydrogen engines offer the possibility of a carbon neutral transportation - a focal point of current propulsion development activities especially for EU and US future concepts. From today's point of view, hydrogen can play an important role in this regard as it is a carbon-free fuel, no CO₂ emissions are produced during its combustion process. Besides, it can be well used for lean burn combustion leading to very low NO_x emissions, a key benefit in combination with an optimized after-treatment system for future ultra-low NO_x legislations of heavy-duty (HD) engines.

Comprehensive investigations using experimental tests and model-based development approach are performed using a six cylinder HD hydrogen engine featuring PFI (port fuel injection) aiming the definition of a high efficiency hydrogen engine concept. The applied predictive hydrogen combustion model is based on previous works of the authors using single cylinder engine measurement data and is extended in the present work to full engines. The calibration and validation of the full engine model used in terms of model-based development is based on experimental test bench data of the six cylinder H2 engine.

An optimization regarding engine calibration (AFR, EGR rates and optimal combustion phase) is carried out while considering knocking. In a next step, efficiency improvement potentials resulting from the application of variable valve timing (VVA) are investigated and the achievable BSFC improvements quantified. As of the results, the use of early intake valve closing (IVC) in the lower load range shows significant benefits in regard of fuel consumption by means of de-throttling and, thus, reducing the charge exchange losses of the engine. Furthermore, the potentials using Miller cycle in the upper load range is also investigated and the potentials for BSFC-improvement quantified. As last part of the paper, an optimal engine map is implemented based on the findings both of operation parameter optimization and the Miller timing investigations.