Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Combined effects of piston bowl geometry and spray pattern on mixing, combustion and emissions of a diesel engine: A numerical approach Shahanwaz Khan a, ⁎ , Rajsekhar Panua b , Probir Kumar Bose c a Department of Mechanical Engineering, Aliah University, New Town, Kolkata 700156, India b Department of Mechanical Engineering, National Institute of Technology, Agartala 799046, India c NSHM Institute of Engineering and Technology, Durgapur 713212, India ARTICLE INFO Keywords: Bowl geometry Combustion Swirl Spray Pollution ABSTRACT In the present work the combine effects of spray angle and the piston bowl geometry on mixing, combustion and emission characteristics of a direct injection diesel engine have been analyzed numerically. The piston bowl geometry is one of the most important factor that affect the air fuel mixing and combustion and emissions in a direct injection diesel engine. Four spray angles 150°, 155°, 160° and 165° and three different piston bowl geometries namely Toroidal Re-entrant Combustion Chamber (TRCC), Toroidal Combustion Chamber (TCC) and the baseline Hemispherical Combustion Chamber (HCC) have been considered for the same compression ratio of 17.5 and with same chamber volume for all three cases. To simulate the in-cylinder flow and combustion computational fluid dynamics (CFD) modeling based AVL FIRE code was performed and experimental results of the baseline hemispherical bowl were used to validate the numerical model. Simulation results show that spray angle significantly affects the mixing and combustion process for all three bowl geometries and the engine having TRCC type of combustion chamber gives better performance. 1. Introduction The internal combustion (IC) engines play a dominant role in the fields of transportation of goods and passengers, powering agricultural equipment and industrial applications. Diesel engines are preferred for heavy-duty usage as they can develop more power at lesser fuel con- sumption. Although the direct injection diesel engine is a better choice among internal combustion engines as a prime mover considering fuel economy and exhaust emissions. Therefore the efforts are being put to improve them further to meet future stringent demands of fuel economy and pollution. In diesel engines, there is a strong relationship between air fuel mixing process and combustion since both the processes occur simultaneously. The most important phenomena are the fuel atomiza- tion, collision and break-up of fuel droplets, their momentum, energy and mass exchange with the air and the droplet-wall interaction. The fluid dynamics in diesel engine is highly transient accompanied by the piston bowl configuration, which make it one of the most important aspects for designing combustion chamber. Therefore, proper under- standing of the effect of the piston bowl shape on the air fuel mixture and thus how it affects the combustion process is required in order to maintain outstanding engine performance and reduce exhaust emis- sions. The performance and emission characteristics of compression igni- tion (CI) engines mainly depend upon the combustion process. Combustion of fuel in diesel engines depends on the efficient fuel ato- mization, to increase the surface area of the fuel in order to attain improved air-fuel mixing and increased evaporation rates. The reduc- tion in the average droplet diameter increases the heat release rates, facilitates ignition, provides excellent vaporization and thereby im- proves combustion efficiency and reduces the pollutant emissions [1]. When there is swirl in the in-cylinder air, the swirl–squish interaction produces a complex turbulent flow field at the end of compression. This interaction is much more intense in re-entrant combustion chamber geometries [2]. The primary factor, which controls the diesel combus- tion, is formation of mixture. The mixture formation is controlled by the characteristics of the injection system, the nature of air swirl, the tur- bulence in cylinder, and the spray characterization [3]. Venkateswaran et al. [4] investigated the effect of re-entrant bowl geometry on the engine performance and combustion efficiency of a turbocharged en- gine at full load conditions. Their result shows that the swirl and Tur- bulent Kinetic Energy with bowl geometry having more re-entrance which is much higher than baseline bowl and it produces better com- bustion and hence better engine performance is found than the baseline bowl which is effective in lowering ISFC and soot emission. Li et al. [5] https://doi.org/10.1016/j.fuel.2018.03.139 Received 6 December 2017; Received in revised form 16 March 2018; Accepted 20 March 2018 ⁎ Corresponding author. E-mail address: shahanwaz77@gmail.com (S. Khan). Fuel 225 (2018) 203–217 0016-2361/ © 2018 Elsevier Ltd. All rights reserved. T