Automotive Science and Engineering

en Role of Nozzle Hole Diameter in Modulating Spray Dynamics and Enhancing Combustion Performance in Reactivity-Controlled Compression Ignition Engines موتور احتراق داخلی Internal Combustion Engines (ICE, ...) پژوهشي Research This study investigates the influence of nozzle hole diameter (NHD) variations on spray dynamics, combustion efficiency, and emissions in a Reactivity-Controlled Compression Ignition (RCCI) engine using Computational Fluid Dynamics (CFD) simulations with the CONVERGE software. The study systematically examines NHDs ranging from 130 µm to 175 µm and evaluates their impact on key parameters such as injection pressure, droplet formation, Sauter Mean Diameter (SMD), and evaporation rates. The results demonstrate that reducing NHD to 130 µm significantly enhances fuel atomization by reducing SMD to 15.49 µm and increasing droplet number by 24%, which in turn accelerates evaporation and improves fuel-air mixing. These effects shorten ignition delays, accelerate combustion, and increase peak cylinder pressures and temperatures. Optimal NHDs (150–160 µm) achieve the highest combustion efficiency (92.04%) and gross indicated efficiency (38.58%). However, further reduction in NHD below this range causes premature ignition, energy dissipation, and higher NOx emissions (10.08 g/kWh) due to elevated combustion temperatures. Conversely, when the NHD increases to 175 µm, the larger droplets formed result in prolonged ignition delays, slower combustion, and lower peak pressures. These effects negatively impact combustion efficiency and promote incomplete combustion, leading to higher HC (15.27 gr/kWh) and CO (4.22 gr/kWh) emissions. Larger NHDs, however, lower NOx emissions to 2.66 gr/kWh due to reduced peak temperatures. This study clearly identifies an optimal NHD range (150–160 µm) that effectively balances droplet size, evaporation rate, combustion timing, and emission reduction, thereby enhancing both engine performance and environmental sustainability. RCCI Engine, Nozzle Hole Diameter, Spray Dynamics, Combustion Efficiency, Emissions 4472 4495 http://ase.iust.ac.ir/browse.php?a_code=A-10-826-1&slc_lang=en&sid=1 Mehran Nazemian Mehran_nazemian@yahoo.com 180031947532846004752 180031947532846004752 Yes Lecturer in the Mechanical Department, Vahdat institute of Higher Education Mehrdad Nazemian en.mehrdad_nazemian@yahoo.com 180031947532846004753 180031947532846004753 No Mechanical Engineering, Sahand University of Technology Mahdi Hosseini Bohloli mehdi.hosseini.bohluli@gmail.com 180031947532846004754 180031947532846004754 No Lecturer in the Mechanical Department, Vahdat institute of Higher Education Hadi Hosseini Bohloli HadiHosseiniBohluli@gmail.com 180031947532846004755 180031947532846004755 No Torbat-e Jam Higher Educational Complex Mohammad Reza HosseiniTazek tazikmohamadreza@gmail.com 180031947532846004756 180031947532846004756 No Lecturer in the Mechanical Department, Vahdat institute of Higher Education