Achieving high-efficiency and clean combustion across the full-load range in an ammonia/diesel dual-fuel direct-injection engine: ICCI strategy and mode transition

As a hydrogen carrier, ammonia is a promising zero-carbon alternative fuel for internal combustion engines (ICEs). However, existing ammonia/diesel dual-fuel (ADDF) research is mostly limited to partial-load optimization and steady-state tests, lacking a full-range combustion framework and transient mode transition verification, which hinders lab-to-engineering translation. This work performs systematic experiments on an ADDF direct-injection (ADDF-DI) engine covering an indicated mean effective pressure (IMEP) range of 2–19 bar. An optimized intelligent charge compression ignition (ICCI) strategy with ammonia energy ratio (AER) over 80% is proposed, and transient mode transition characteristics are investigated. Results show that the ICCI strategy extends the stable operating limit to IMEP of 19 bar, with a peak indicated thermal efficiency (ITE) of 53.1% and the combustion efficiency over 99%. The inherent ITE–NO x trade-off is overcome, while unburned ammonia, N 2 O and NO x are controlled below 2, 0.03 and 5 g/kWh at high loads, respectively, achieving nearly 80% carbon reduction versus conventional diesel combustion (CDC). The forward CDC–ICCI transition is completed within 3 cycles at IMEP of 6 bar, and the reverse transition stabilizes in 1 cycle, with the coefficient of variation of IMEP below 2% at the optimal AER of 45%. Excellent load-following performance is validated via bidirectional load step transitions between 6 and 8 bar. This study establishes a full-range ICCI control framework for ADDF-DI engines, providing theoretical and technical support for the application of the ICCI mode.