Hydrogen energy share enhancement in a heavy duty diesel engine under RCCI combustion fueled with natural gas and diesel oil Hadi Mabadi Rahimi a , Seyed Ali Jazayeri b,* , Mojtaba Ebrahimi a a Department of Mechanical Engineering, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran b Faculty of Mechanical Engineering, K. N. Toosi University of Technology, Tehran, Iran highlights graphical abstract  Reduction in fuel consumption by enhancing hydrogen energy share.  No exposure to diesel knocks.  Achieving the gross indicated effi- ciency over 50%.  No significant engine power losses.  Satisfying EURO VI level for CO and UHC, and EPA level for Formaldehyde. article info Article history: Received 28 January 2020 Received in revised form 16 April 2020 Accepted 29 April 2020 Available online xxx Keywords: RCCI Combustion Natural gas Diesel engine Hydrogen Syngas abstract The aim of this study is to enhance hydrogen energy share in a RCCI engine. The engine under consideration is fueled with diesel oil and natural gas enriched with hydrogen or syngas and is set to operate at 9.4 bar gross indicated mean effective pressure (Mid- Load). The syngas used in this study consists of hydrogen and carbon monoxide which are mixed together on a volumetric ratio of 80:20. A fixed amount of diesel oil is injected per cycle into the combustion chamber of the RCCI engine. Based on two different strategies, hydrogen or syngas mixed with exhaust gas recirculation are admitted gradually along with natural gas while ensuring that always the low temperature combustion concept is fulfilled. The RCCI engine operation is simulated through commercial software coupled with chemical ki- netics solver. The simulation results show that without any engine diesel knock occur- rence, by adding hydrogen to natural gas, the share of hydrogen energy could be increased up to 40.43% while the engine power output is reduced only by about 1%. Also, syngas addition to natural gas causes that the share of hydrogen energy could be increased up to 27.05% while improves the engine power more than 4%. At the same time, by considering two mentioned strategies, the overall hydrocarbon fuel consumption per cycle can be reduced by up to 46.60% and 33.86%, respectively. Moreover, having the gross indicated * Corresponding author. E-mail address: JAZAYERI@kntu.ac.ir (S.A. Jazayeri). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2020.04.263 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Mabadi Rahimi H et al., Hydrogen energy share enhancement in a heavy duty diesel engine under RCCI combustion fueled with natural gas and diesel oil, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2020.04.263