Investigating the combustion, NO emissions and cyclic variability (CCV) in SI engine fueled with ammonia-hydrogen blends by two-zone quasi-dimensional model with two CCV governing mechanisms

The cyclic variability (CCV) of performance, combustion, and nitric oxide (NO) emissions in spark-ignition (SI) engine fueled with various ammonia-hydrogen blends is investigated, employing previously validated, in-house, quasi-dimensional turbulent-combustion model tracking the flame-front propagation in engine-cylinder, expanded herein to treat ammonia-hydrogen blends. The model is validated successfully at steady-state against experimental data and then enhanced to study behavior of same attributes under CCV conditions comparing against experimental data, considering influence of two governing mechanisms, flame-kernel turbulence and fuel-air ratio variations. The steady-state numerical results included cylinder-pressure (CP), indicated mean effective pressure (IMEP), combustion-stages duration and NO emissions, using for CCV investigation mean-values, coefficients of variation, frequency-distributions and scatter-plot diagrams. The model allows computation of e.g. turbulent-intensity, integral-length and flame-speed, which afford elucidating the effects of ammonia enrichment with hydrogen. The COV of CP and IMEP decrease with hydrogen addition, peak temperatures COV are ∼1 % and for NO up to 40 %.