Effects of hydrogen and methane addition on combustion characteristics, emissions, and performance of a CI engine Yasin Karag € oz a,** , _ Ilker Gu ¨ ler b , Tarkan Sandalcı a , Levent Yu ¨ ksek a , Ahmet Selim Dalkılıc ¸ c,* , Somchai Wongwises d a Automotive Division, Department of Mechanical Engineering, Mechanical Engineering Faculty, Yıldız Technical University, Yildiz, Besiktas, Istanbul, 34349, Turkey b Tu ¨ rk Trakt€ or ve Ziraat Makineleri A.S ‚ , Turkey c Heat and Thermodynamics Division, Department of Mechanical Engineering, Mechanical Engineering Faculty, Yildiz Technical University, Yildiz, Besiktas, Istanbul 34349, Turkey d Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab. (FUTURE), Department of Mechanical Engineering, King Mongkut's University of Technology Thonburi, Bangmod, Bangkok 10140, Thailand article info Article history: Received 13 August 2015 Received in revised form 30 October 2015 Accepted 22 November 2015 Available online 24 December 2015 Keywords: Hydrogen Methane Diesel engine NO x THC CO Smoke abstract In this study, while a hydrogen þ methane mixture in the gas phase (30% H 2 þ 70% CH 4 in moles) is injected from an intake port by a gas injector, ignition is supplied with diesel fuel sprayed from a diesel injector. The energy content of the sprayed gas fuel is modified to constitute 0% (only diesel fuel), 15%, 40%, and 75% of the total fuel energy content. All tests are conducted at 1500 rpm stable engine speed and in full-load condition. The effects of energy content modification of hydrogen þ methane gas fuel on engine performance, emissions, and combustion are observed. Both NO x and soot emissions are taken under control with 15% and 40% energy content rates in the gas fuel compared to the diesel-only condition. Although an increase is observed in CO and THC emissions with gas fuel addition compared to the diesel- only condition, an improvement is considered compared to the results obtained for only methane fuel usage with diesel fuel. Moreover, gas fuel mixtures reach a high value (75% energy content) as peak cylinder gas pressure decreases. A single-phase heat release was observed, and the diesel combustion characteristic of the engine was converted into gasoline combustion with the addition of 75% hydrogen þ methane as the energy basis. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Introduction Fast depletion of fossil fuels due to increasing energy de- mand is causing the price of petroleum fuels to increase. Also, stringent emission regulations for energy efficiency and environmental concerns are accelerating the number of studies on alternative fuel. According to a European Union Commission White Paper Report, a 60% decrease is targeted on greenhouse gas emissions generated from transportation * Corresponding author. Tel.: þ90 212 383 2821; fax: þ90 212 383 2765. ** Corresponding author. Tel.: þ90 212 383 2901; fax: þ90 212 383 2765. E-mail addresses: ykaragoz@yildiz.edu.tr (Y. Karag€ oz), dalkilic@yildiz.edu.tr (A.S. Dalkılıc ¸). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 41 (2016) 1313 e1325 http://dx.doi.org/10.1016/j.ijhydene.2015.11.112 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.