Effect of reformed biogas as a low reactivity fuel on performance and emissions of a RCCI engine with reformed biogas/diesel dual-fuel combustion Reza Mahmoodi a,** , Mortaza Yari b,* , Jafar Ghafouri a , Kamran Poorghasemi c a Faculty of Mechanical Engineering, Islamic Azad University, Tabriz Branch, Tabriz, Iran b Faculty of Mechanical Engineering, University of Tabriz, Tabriz, Iran c Department of Mechanical Engineering, Islamic Azad University, Shabestar Branch, Shabestar, Iran highlights  A novel investigation of impact of actual syngas on RCCI engine is performed.  Thermodynamic models are analysed for each type of syngas.  Reduction of NOx and increase of other emissions for actual syngas are proven.  Using R.BG in a RCCI engine causes a reduction in the mean combustion temperature.  large reduction in NOx emission by enhancing the R.BG substitution ratio. article info Article history: Received 31 May 2020 Received in revised form 25 August 2020 Accepted 22 September 2020 Available online xxx Keywords: RCCI engine Combustion Biogas Emissions Reformed biogas abstract Biogas can be used as a less expensive continuance renewable fuel in internal combustion engines. However, variety in raw materials and process of biogas production results in different components and percentages of various elements, including methane. These differences make it difficult to control the combustion, effectively, in internal combustion engines. In this research, under cleaning and reforming process, biogas components were fixed. Then the effect of reformed biogas (R.BG) was investigated, numerically, on the combustion behavior, performance and emissions characteristics of a RCCI engine. A 3D- computational modeling has been performed to validate a single-cylinder compression ignition engine in conventional diesel and dual-fuel operations at 9 bar IMEP, 1300 rpm. Then, the combustion model of the RCCI engine was simulated by replacing diesel fuel with 20%, 40% and 60% of R.BG as a low reactivity fuel while remaining constant input total fuel energy per cycle. The results demonstrated that when the R.BG substitution ratio in- creases with a constant equivalence ratio of 0.43, the mean combustion temperature de- creases to 1354 K, 1312 K, 1292 K which are about 3.5%, 6.6%, 7.9% lower than the conventional diesel combustion, respectively. The maximum in-cylinder pressure in- creases up to 22.63%. Instead, it results in 2.3%, 7.9%, and 14.5% engine power output losses, respectively. Also, the NOx emission, against CO, is decreased by 50%. Soot and UHC emissions were found to be slightly decreased while was used R.BG more than 40%. © 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. * Corresponding author. should be addressed Faculty of Mechanical Engineering, University of Tabriz, Tabriz, Iran. ** Corresponding author. Faculty of Mechanical Engineering, Islamic Azad university, Tabriz Branch, Tabriz, Iran. E-mail addresses: stu.r.mahmoodi@iaut.ac.ir (R. Mahmoodi), myari@tabrizu.ac.ir (M. Yari), jafarghafouri@iaut.ac.ir (J. Ghafouri), Kamran.poorghasemi@gmail.com (K. Poorghasemi). 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.2020.09.183 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Mahmoodi R et al., Effect of reformed biogas as a low reactivity fuel on performance and emissions of a RCCI engine with reformed biogas/diesel dual-fuel combustion, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2020.09.183