Multiphase combustion modeling of ammonia–diesel RCCI engines using RANS,DES,and LES turbulence models

Abstract

This work quantifies how spray atomization and vaporization govern ammonia–diesel RCCI combustion by comparing RANS (RNG k–ε), DES (SST k–ω), and LES (dynamic Smagorinsky). Beyond validation against in-cylinder pressure, HRR, CA50, and ITE, and pollutant emissions, we analyze DV10/DV50/DV90, SMD, parcel count, and penetration to expose turbulence–spray–chemistry couplings. LES Captures fine-scale dynamics, including rapid DV50 reduction (≈28 to ≈11.5 µm), enhanced secondary breakup, and core instabilities, generating >160,000 parcels and accelerating vaporization. These resolved phenomena translate into superior combustion fidelity, closely matching experiment peak pressure (84.2 vs 85 bar), CA50 (10.24° CA), ITE (37.218%), IMEP (≈9.1 bar), while accurately predicting emission (UHC: 0.48 g/kWh vs 0.46 g/kWh, NO: 2.15 g/kWh vs 2.20 g/kWh). DES offers intermediate fidelity, whereas RANS retains oversized droplets, slow vaporization, and underprediction of combustion intensity and The total computational expenditure amounted to approximately 410 CPU-h for RANS, 1240 CPU-h for DES, and 3240 CPU-h for LES, using meshes ranging from 200,000 to 8,000,000 cells.