Quantum chemical insights into ammonia/diesel dual fuel combustion in CO2/O2 atmospheres: Model and experiment

To investigate the influence of CO2 on ammonia (NH3)/diesel dual-fuel combustion in a CO2/O2 atmosphere, a quantum chemical (QC) model is developed that incorporates reactions between CO2 and primary thermal decomposition products of NH3/diesel. Reactant and transition-state structures are optimized using B2PLYP and CCSD(T), and four new pathways (NH + CO2 → HNO + CO, NH2 + CO2 → HNCOOH, NH2 + CO2 → HNCO + OH, NH2 + CO2 → CO + H2NO) are added to a simplified NH3/diesel (n-C7H16) mechanism, yielding a QC-based kinetic model. A visual rapid compressor platform is constructed to take measurements at an initial pressure of 1.01 MPa and an initial temperature of 333 K for various NH3/diesel energy ratios (1:9, 2:8, 3:7, and 4:6) and CO2/O2 mixtures (35% CO2/65% O2, 39% CO2/61% O2, 43% CO2/57% O2, and 47% CO2/53% O2) at an equivalence ratio of 1.5. Potential energy surfaces, ignition delay, sensitivity, and reaction pathways are analyzed with the QC model and experiments. The model reproduces ignition delay times with a maximum error of 8.26%. Owing to its low barrier (15.06 kcal/mol) and high stability, pathway R1 dominates NH3/diesel combustion. Increasing NH3 strengthens competition with OH via NH3 → NH2 → NH → HNCO, suppressing chain-branching, while higher CO2 dilutes reactive intermediates, decreases n-heptane formation, and weakens combustion intensity.