Numerical study of combustion and emission characteristics of dual-fuel engines using 3D-CFD models coupled with chemical kinetics Amin Maghbouli a , Rahim Khoshbakhti Saray b,⇑ , Sina Shafee c , Jafar Ghafouri d a Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, Singapore b Mechanical Engineering Faculty, Sahand University of Technology, Tabriz, Iran c Department of Mechanical Engineering, Faculty of Natural and Applied Sciences, Middle East Technical University, Ankara, Turkey d Azad University of Tabriz, Azad University Departments, Tabriz, Iran highlights " Zheng and Yao’s mechanism can capture spray combustion of fuel rich regions. " Cylinder peak pressure is delayed by shifting diesel to dual-fuel combustion mode. " IMEP and ITE are increased by applying higher amount of pilot fuel. " Higher NO x and CO levels are resulted by increasing pilot fuel quantity. article info Article history: Received 23 February 2011 Received in revised form 29 September 2012 Accepted 23 October 2012 Available online 20 November 2012 Keywords: Dual-fuel KIVA Combustion Chemical kinetics Pilot fuel abstract Dual-fuel combustion provides a relatively easy and inexpensive alternative to conventional diesel engine combustion by drastically reducing fuel consumption with comparable performance characteris- tics. Accurate simulation of the dual-fuel combustion requires utilization of a detailed chemistry com- bined with a flow simulation code. In the present study, the combustion process within the diesel and diesel/gas dual-fuel engine is investigated by use of a coupled 3D-CFD/chemical kinetics framework. In this study, methane and n-heptane are used as representatives of the natural gas and diesel fuels. The multi-dimensional KIVA-3V code, with modified combustion and heat transfer models, incorporates a chemical kinetics mechanism for n-heptane and methane oxidation chemistry. The source terms in energy and species conservation equations due to chemical reactions are calculated by integrating the CHEMKIN chemistry solver into the KIVA code. The model is applied to simulation of a medium duty dual-fuel converted diesel engine. A chemical kinetics mechanism which consists of 42 species and 57 reactions is used for prediction of n-heptane oxidation chemistry. Simulation of dual-fuel combustion is performed using the same mechanism with addition of a series of major methane oxidation pathways. The results show that Zheng and Yao’s n-heptane mechanism which had been previously validated in their work, can model the diesel and dual-fuel combustion, where fuel-rich zones are present. The pre- dictive model of this study is validated using available published experimental data. Results show that pressure and ignition delay predictions are in good agreement with experiments. Based on constant total mixture input energy in dual-fuel combustion, increasing pilot fuel amount leads to shorter ignition delay and peak pressure increment. It is found that concentrations of NO x and CO emissions tend to increase at higher pilot fuel injection quantities. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Although cutting edge studies on alternative power generation units and technologies such as fuel-cells and hybrid-automobiles are carrying significant amount of research projects, they do not seem to completely take the role of internal combustion engines in the near future. Therefore a considerable deal of research is concen- trated on optimization of conventional engines. Based on ongoing numerical calculations and recent achievements in practical appli- cations, dual-fuel compression ignition engines are nominated to meet requirements of the strict emission regulations. In practice, the dual-fuel engines are conversion of conventional diesel engines while NG provides majority of chemical energy. Injection of diesel as pilot fuel is used here to ignite NG and air mixture [1,2]. 0016-2361/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2012.10.055 ⇑ Corresponding author. Tel./fax: +98 412 3459065. E-mail addresses: mpeaminm@nus.edu.sg (A. Maghbouli), khoshbakhti@sut.ac.ir (R.K. Saray), sina.shafee@metu.edu.tr (S. Shafee), gh_jafar@yahoo.com (J. Ghafouri). Fuel 106 (2013) 98–105 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel