Emission characteristics of using HCNG in the internal combustion engine with minimum pilot diesel injection for greater fuel economy Kasidet Pichayapat * , Sukruedee Sukchai, Sahataya Thongsan, Anan Pongtornkulpanich School of Renewable Energy Technology, Naresuan University, Phitsanulok 65000, Thailand article info Article history: Received 13 December 2013 Received in revised form 29 May 2014 Accepted 1 June 2014 Available online 1 July 2014 Keywords: HCNG Emissions Diesel dual fuel HCNG blended Internal combustion engine Electrolyzer abstract Hydrogen and Compressed Natural Gas are great alternatives to the pure fossil fuels. Many researches confirm the advantages of using hydrogen and natural gas blended together for the internal combustion engine in both areas of improving performances and reducing emission levels. In a short to medium range terms, the air pollution throughout the globe could be significantly reduced by using HCNG in the internal combustion engine and in many other applications with the substitution of using HCNG as a main source of fuel or as a secondary source of fuel such as the dual fuel operation system in the diesel vehicle. This paper investigates the emission characteristics of using HCNG as a secondary source of fuels on a EURO 4 diesel vehicle with four cylinders of 2494 cc displacement D4D commonrail direct injection diesel engine comparing to the original diesel operation with diesel and HCNG blended dual fuel operation. The experiments were conducted with minimum pilot diesel injection into the engine and maximum additional HCNG into the engine with using H 2 electrolyzer for hydrogen supplies. In this experiment, the pilot diesel and HCNG blended were operated with special designed closed loop stepping motor diesel to CNG dual fuel system and hydrogen electrolyzer for the internal combustion engine. The results indicated that the average CO emission decreased by 12.97%, HC emission decreased by 15.84%, NO x emission decreased by 1.16% and PM emission decreased by 9.14% with the diesel HCNG dual fuel mode comparing to the pure diesel operation from low RPM (800) to highest RPM (4000). Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction With constantly increasing in energy needs in the trans- portation sector, fossil fuels will not be enough for sustainable world economy. Along with much higher pollution levels as comparing to the past, more cooperation from the local levels up to the international levels have been formed with the aim of imposing more stringent emission legislation to control the emission levels globally. Through the international coopera- tion, international environmental policies have been formed with regulations concerning the air pollutions and other environmental issues. * Corresponding author. Tel./fax: þ66 55 963182. E-mail addresses: kasidet_p@hotmail.com, kasidet@straightnine.com (K. Pichayapat). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 39 (2014) 12182 e12186 http://dx.doi.org/10.1016/j.ijhydene.2014.06.004 0360-3199/Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.