RECENT TRENDS IN BIOPLASTICS Computational analysis of turbulence enhancement in a compression ignition engine with modified inlet design Nandakumar Chinnamuthu 1 & Saravanan Chidambaram Ganapathy 2 & Vikneswaran Malaiperumal 2 & Edwin Geo Varuvel 3 & Vallinayagam Raman 4 & Poonguzhali Boologarajan 5 & Ashok Kannan 6 Received: 30 April 2020 /Accepted: 15 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract This study aims to enhance the turbulence of direct injection (DI) diesel engine by modifying the inlet manifold design with an inclined nozzle-like provision angles of 30°, 60°, and 90° along with its regular intake system. Numerical analysis was carried out using the computational fluid dynamics package (STAR-CD libraries of es-ice) to study the flow field and combustion charac- teristic with the modified intake manifold geometries. The computational investigation was carried out for both single and double pass conditions at 1500 rpm under high-load operating condition (5.2 kW). The computational results showed that the velocity magnitude of modified single pass intake manifold increases by about 10% that results in higher turbulence even near the point of fuel injection. Through the modification in the inlet manifold, the combustion parameters such as in-cylinder pressure and in- cylinder temperature are increased as compared to the standard manifold for the same quantity of fuel injected per cycle. In summary, the 60° modified manifold with a single pass shows better combustion and emission characteristics compared to that of regular inflow manifolds due to the improvement in turbulence levels. Keywords Diesel engine . Inlet manifold . In-cylinder flow . CFD . NOx . Soot Abbreviations CFD Computational fluid dynamics DI Direct injection CI Compression ignition TKE Turbulent kinetic energy ECFM Extended coherent flame model MARS Monotone advection and reconstruction TDC Top dead centre aTDC After top dead centre bTDC Before top dead centre CO Carbon monoxide HC Hydrocarbon CO 2 Carbon dioxide NOx Oxides of nitrogen Introduction In compression ignition (CI) engines, the air-fuel mixing pro- cess and the subsequent combustion process are governed by the in-cylinder flow field, fuel spray pattern, air/fuel mixing, and other such characteristics (Heywood 1998). The processes such as spray break-up, droplet evaporation, and air-fuel in- teraction are mainly controlled by the local flow field charac- teristics in the neighborhood of the fuel droplets formed. The in-cylinder airflow process strongly influences the diesel com- bustion process right from the auto-ignition to fuel oxidation Responsible Editor: Philippe Garrigues * Edwin Geo Varuvel vedwingeo@gmail.com 1 Department of Production Technology, Madras Institute of Technology, Anna University, MIT campus, Chennai, Tamilnadu, India 2 Department of Mechanical Engineering, Annamalai University, Annamalainagar, Tamilnadu, India 3 Green Vehicle Technology Research Centre, Department of Automobile Engineering, SRM Institute of Science and Technology, Kattankulathur, Tamilnadu 603203, India 4 Clean Combustion Research Centre, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia 5 Mechanical Department, Government Polytechnic College, Madurai, Tamilnadu, India 6 Department of Mechanical Engineering, Pondicherry Engineering College, Puducherry, India Environmental Science and Pollution Research https://doi.org/10.1007/s11356-020-10157-9