SINERGI Vol. 27, No. 2, June 2023: 171-178 http://publikasi.mercubuana.ac.id/index.php/sinergi http://doi.org/10.22441/sinergi.2023.2.004 A. Martin et al., Utilizing waste heat gasoline engine in the design and fabrication of a fin … 171 Utilizing waste heat gasoline engine in the design and fabrication of a fin and tube evaporator for the Organic Rankine Cycle (ORC) Awaludin Martin*, Rudi Hartono, Reza Asrian Department of Mechanical Engineering, Faculty of Engineering, Riau University, Indonesia Abstract The excessive consumption of fossil fuels is causing environmental problems, which can be addressed by utilizing renewable energy sources such as hydro energy, biomass, solar heat, geothermal, and waste heat. In particular, the exhaust gas from gasoline engines presents an opportunity for energy recovery, as only 25% of the energy is utilized while the remaining 75% is wasted. A fin and tube type evaporator was designed, manufactured, and tested to utilize this exhaust gas in an Organic Rankine Cycle (ORC) system. The evaporator was designed with an outer tube diameter of 9.525 mm and a total tube length of 41.4 m, featuring 90 tubes and 135 fins with a total area of 14,325 m2. It achieved an average effectiveness of 94.33%. The results showed that the waste heat from the exhaust gas of a gasoline engine could be used as a source of energy in an ORC system with an efficiency of 2.13%. It results in 7.02 kJ/s of energy absorbed by the evaporator and a net power generated of 0.15 kJ/s. This research demonstrates the potential for utilizing waste heat from gasoline engines as an energy source to generate electricity. This is an open access article under the CC BY-SA license Keywords: Evaporator; Organic Rankine Cycle; Waste Heat; Article History: Received: May 25, 2022 Revised: October 14, 2022 Accepted: October 23, 2022 Published: June 2, 2023 Corresponding Author: Awaludin Martin Department of Mechanical Engineering, Faculty of Engineering, Riau University, Indonesia Email: awaludinmartin01@gmail.com INTRODUCTION Electricity demand is rising, driven by several factors, such as population growth, economic development, and technological progress [1][2]. In Indonesia, the population has increased from 238 million in 2010 to 268 million in 2019, which is expected to further increase the per capita demand for electricity [3]. Projections from the National Energy Council indicate that the demand for electricity per capita is expected to reach 2,030 kWh/capita in 2025 and 6,723 kWh/capita in 2050. These projections are still within the targets the National Energy Policy set, which aims for 2,500 kWh/capita in 2025 and 7,500 kWh/capita in 2050 [4]. Indonesia's national energy consumption for electricity generation in 2018 was primarily sourced from fossil fuels, with petroleum, coal, and natural gas accounting for 7.13%, 48.65%, and 29.15% of the total consumption, respectively, totalling 84.93% [5]. However, using these fuels has led to various environmental problems, such as air pollution, ozone layer depletion, acid rain, and global warming. These problems seriously affect human health, leading to respiratory illnesses, inflammation, heart diseases, and cancer. Additionally, the consumption of fossil fuels is unsustainable due to their limited availability [6, 7, 8]. As global energy demand continues to rise, finding sustainable solutions that reduce reliance on fossil fuels is becoming increasingly important. One promising approach is to increase the utilization of renewable energy sources, such as hydropower, ocean power, wind energy, biomass, solar power, and waste management [ 9][10]. Recent years have seen significant research efforts directed towards converting low- temperature and high-pressure heat into usable energy. Waste heat recovery has emerged as a promising technology among these approaches. Waste heat can be derived from various thermal