اميرحسين فخاري

Researchers are currently developing technologies aimed at eliminating fuels containing carbon in their molecular structures, thereby effectively minimizing the emission of carbon oxides into the atmosphere. Carbon-free fuels such as ammonia an‎d hydrogen have attracted significant attention due to their potential applications in compression ignition (CI) engines. In this study, a numerical simulation of an RCCI (Reactivity-Controlled Compression Ignition) engine was conducted using ammonia, hydrogen, an‎d diesel as fuels, employing a combined chemical kinetic mechanism for combustion reactions. In the first phase, the effects of parameters such as various ammonia energy fractions, diesel injection timing, an‎d the temperature at intake valve closing (TIVC) on engine performance an‎d emissions were analyzed. In the second phase, under optimized conditions, including a diesel injection timing of 60° bTDC an‎d a 20% diesel energy share, the influence of hydrogen addition (0–30% energy fraction) an‎d TIVC reduction was investigated. Results showed that increasing the ammonia energy fraction from 30% to 70% significantly improved the indicated mean effective pressure (IMEP), while CO, HC, unburned ammonia, an‎d N₂O emissions remained low. Additionally, higher ammonia fractions led to a remarkable reduction in NOx an‎d CO₂ emissions. The RCCI combustion mode exhibited superior efficiency an‎d lower pollutant emissions compared to conventional dual-fuel combustion. Hydrogen enrichment further enhanced combustion efficiency an‎d IMEP, while simultaneously reducing exhaust emissions. When using 80% ammonia energy fraction without hydrogen, a minimum intake temperature of 440 K was required for complete combustion, an‎d NOx emissions increased to around 20 g/kWh. With the addition of 20% hydrogen, the required temperature decreased to 380 K, an‎d NOx emissions were reduced to approximately 13 g/kWh, while N₂O remained nearly constant. Subsequently, a reduced chemical kinetic mechanism for ammonia/methane–diesel combustion was developed, consisting of 188 species an‎d 1320 reactions. The mechanism was optimized for engine-relevant conditions, including high pressures, low temperatures, an‎d varying fuel compositions, an‎d was calibrated using experimental data for ignition delay time (IDT) an‎d laminar flame speed (LFS). CFD simulations employing this mechanism showed good agreement with experimental data. The proposed kinetic mechanism enables accurate simulation of dual-fuel RCCI engine performance an‎d emission characteristics

احتراق RCCI , آمونياك , هيدروژن , آلايندگي , توسعه مكانيزم سينتيك شيميايي

RCCI combustion , Ammonia , Hydrogen , Emissions , Chemical Kinetic Mechanism Development

Amir Hossein Fakhari

Ayat Gharehghani