This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. Automotive Experiences 507 Automotive Experiences Vol. 5 No. 3 (2022) pp. 507-527 p-ISSN: 2615-6202 e-ISSN: 2615-6636 Combustion and Emission Characteristics of CNG-Diesel Dual Fuel Engine with Variation of Air Fuel Ratio Dori Yuvenda 1,2 , Bambang Sudarmanta 3 , Jamaludin 3 , Oki Muraza 4 , Randi Purnama Putra 1,2 , Remon Lapisa 1,2 , Krismadinata 1,5 , Rahadian Zainul 1,6 , Asnil 1,5 , Muji Setiyo 7,8 , Sri Rizki Putri Primandari 1,2 1 Centre For Energy and Power Electronics Research (CEPER), Universitas Negeri Padang, 25131, Indonesia 2 Department of Mechanical Engineering, Universitas Negeri Padang, 25131, Indonesia 3 Department of Mechanical Engineering, Institut Teknologi Sepuluh Nopember, 60111, Indonesia 4 Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, 31261, Saudi Arabia 5 Department Electrical Engineering, Universitas Negeri Padang, 25131, Indonesia 6 Department Chemical, Universitas Negeri Padang, 25131, Indonesia 7 Department of Automotive Engineering, Universitas Muhammadiyah Magelang, 56126, Indonesia 8 Center of Energy for Society and Industry (CESI), Universitas Muhammadiyah Magelang, Indonesia doriyuvenda@ft.unp.ac.id https://doi.org/10.31603/ae.7807 Published by Automotive Laboratory of Universitas Muhammadiyah Magelang collaboration with Association of Indonesian Vocational Educators (AIVE) Abstract Article Info Submitted: 05/09/2022 Revised: 03/12/2022 Accepted: 05/12/2022 Online first: 18/12/2022 Compressed natural gas (CNG) is a popular alternative fuel because of its more environmentally friendly properties than fossil fuels , including applications in diesel engines. However, supplying too much compressed natural gas fuel causes poor engine performance and emissions due to a decrease in the air-fuel ratio on the dual-fuel engine. The addition of air using electric superchargers was done to return the air-fuel ratio to ideal conditions. Lambda value (λ) was variation under low load (1.52 to 2.71), medium load (1.18 to 2.17), and high load (0.94 to 2.17) on a CNG-diesel dual fuel engine. The addition of pure air in each load can increase combustion stability in certain lambda, which was indicated by an increase in thermal efficiency, heat release rate, and a decrease in ignition delay, combustion duration, hydrocarbon, and carbon monoxide emissions. Keywords: CNG, Engine performance; Emission; Air fuel ratio; Thermal efficiency 1. Introduction Anxiety about global warming gets special attention in every country, especially Indonesia. One of the biggest sources of increasing world temperature was exhaust gas from an internal combustion engine [1]. Also, it has impact on the greenhouse effect, emissions were also harmful to human health [2], and the environment [3], especially nitrogen oxide (NOx), hydrocarbon (HC), carbon monoxide (CO), and sulfur oxide (SOx) gases [4]. Thus, strict regulation was needed on exhaust gases produced by an internal combustion engine. The diesel engine was one of the internal combustion engine (ICE) that produce very high nitrogen oxide (NOx) and particulate matter (PM) emissions [5]–[10]. Various efforts have been made by automotive researchers to reduce NOx and PM emissions on diesel engines, such as exhaust gas recirculation (EGR) [11], [12], direct water injection [13] and dual fuel systems [14]– [18]. Currently, dual fuel system technology in a diesel engine was more developed, because it was more effective in reducing NOx and particulate matter emissions, while also reducing fossil fuel consumption by substituting alternative fuels. An alternative fuel that was widely used in dual fuel systems was natural gas [19], [20]. The reason for utilizing natural gas was its availability which was quite large, especially in Indonesia [21]–[23].