Energy efficient piston configuration for effective air motion – A CFD study Antony Raj Gnana Sagaya Raj, Jawali Maharudrappa Mallikarjuna, Venkitachalam Ganesan ⇑ Internal Combustion Engines Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India highlights " All piston crown show similar flow pattern for experimental and simulated studies. " Piston position plays a predominant role in the air pattern inside the cylinder. " The flat bowl piston shows higher TKE compared to all other piston crown shape. " The turbulence intensity and length scale are higher for flat bowl piston. " The quantitative error between the CFD and PIV analysis is about 5%. article info Article history: Received 25 November 2011 Received in revised form 30 May 2012 Accepted 19 July 2012 Available online 15 September 2012 Keywords: Diesel engine CFD Piston configuration PIV In-cylinder air motion abstract Air motion inside the cylinder is very important from the point of view of energy efficiency. In this direc- tion, piston configuration plays a very crucial role. This study is concerned with the CFD analysis of in- cylinder air motion coupled with the comparison of predicted results with the experimental results avail- able in the literature. Four configurations viz., flat, inclined, centre bowl and inclined offset bowl pistons have been studied. For numerical analysis STAR-CD CFD software has been used. Experimental results available in the literature for comparison are obtained by PIV measurements. From this study, it is con- cluded that a centre bowl on flat piston is found to be the best from the point of view of tumble ratio, turbulent kinetic energy, turbulent intensity and turbulent length scale which play very important role in imparting proper air motion, there by increasing the energy efficiency of the engine. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Development of a fuel efficient and less polluting engine is an important goal of researchers worldwide in automotive industry. Due to the concerns of global warming and to cut down the emis- sion of green house gases, there is an urgent need to achieve sub- stantial improvements in fuel economy of the internal combustion engines. In this direction, in-cylinder fluid dynamics plays a crucial role in the energy efficient combustion especially in compression ignition direct injection (CIDI) engines. The fluid motion inside the engine cylinder is inherently unsteady, turbulent and three dimensional. The gas motion is unstable during the intake and compression processes and breaks down into three dimensional turbulent motions. Therefore, proper understanding of in-cylinder air motion and also the effect of bowl shape are required to im- prove performance and reduce emissions without compromising fuel economy. Nowadays, a number of cold and hot flow CFD simulation stud- ies have been carried out to understand the in-cylinder flow field, combustion and emission processes in IC engines [1–4]. Investiga- tions have shown that the complex flow structure like swirl, vortic- ity, tumble and turbulence exist inside the engine cylinder even after the closure of the intake valve [5]. Nordgren et al. [6] studied the in-cylinder air motion through experimental and theoretical methods viz., PIV and CFD and have reported that the peak value of swirl occurs at about 50 CAD before TDC and the maximum va- lue of vorticity and turbulence exist during the later stage of com- pression stroke. Huang et al. [7] diagnosed the evolution processes of in-cylinder tumble and swirl flows on a motored two valve, sin- gle cylinder, four-stroke engines through PIV technique and con- cluded that the strength of the tumble motion is maximum between 120 CAD and 180 CAD before BDC. The vortex structures created during the intake stroke has a major effect on the turbu- lence during the end stage of compression process, since turbu- lence is directly proportional to the rate of decay of the tumble. Faure et al. [8] applied two experimental techniques (LDA and PIV) on direct injection gasoline engine to study the in-cylinder tumbling flow structure and reported that the flow structure 0306-2619/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2012.07.022 ⇑ Corresponding author. Tel.: +91 44 22574657; fax: +91 44 22574652. E-mail address: vganesan@iitm.ac.in (V. Ganesan). Applied Energy 102 (2013) 347–354 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy