**1. Introduction**

Presently, increasing world energy demand is causing an increase in the consumption of fossil fuels, which also causes a negative impact on global warming and the overall environment. Moreover, fossil fuel resources continue to deplete every year due to their non-renewable nature [1,2]. This has prompted researchers to investigate alternative fuels both from waste materials and renewable feedstock to reduce dependence on fossil fuel and ensuing air pollution. Some of the renewable energy sources that have been widely explored include biofuel [3], wind [4], solar [5], geothermal [4], and nuclear energy. Each type of energy sources possesses some advantages and drawbacks. For example, solar and wind energy suffer difficulties in energy storage since they are unstable and available only at

certain times [6]. This can be addressed by appropriate energy storage material that can save a large amount of energy, such as phase-change materials that can replace current batteries [7]. On the other hand, energy coming from agricultural waste, or tropical biodiversity of non-edible origin, is still one of the best choices in developing countries, such as Indonesia and Malaysia, as they directly address the issue of energy sustainability [8,9].

Plastic has been widely produced and used since the early 20th century. The use of plastic has risen rapidly and it is presently used in almost every economic sector for packaging products, as it is an easy material to procure as well as to form into an end product. At present, the use of plastic materials in western European countries has reached 60 kg/person/year and 80 kg/person/year in the USA, while in India it is only 2 kg/person/year [10]. High plastic waste is related to population and waste management. Around 80% of plastic waste comes from the mainland. In 2019, waste in Indonesia reached 68 million tons, with 14% of this being plastic waste, at 9.52 million tons. With an estimated 0.7 kg/day of garbage produced by each person, the average daily amount of rubbish dumped in metropolitan cities is approximately 1300 tons/day (the population is more than 1 million) [11]. Furthermore, Indonesia is second highest dumper of plastic waste into world's oceans, after China, depositing approximately 1.29 million tons per year, compared to China's 3.53 million tons per year [11,12]. Managing plastic waste has always been a big problem. Besides being non-biodegradable and difficult to manage, plastic waste can also pollute soil. Standard plastic bags generally made from poly-ethylene are not biodegradable. However, photodegradation can occur in plastics. When exposed to ultraviolet rays from sunlight, the structure becomes fragile and breaks into pieces, which takes a long time. Experts estimate that at least 500 to 1000 years are needed for this decomposition to take place [11]. The negative effects of trash in the ocean has resulted in many marine biota experiencing metabolic disorders, irritation of the digestive system, and death resulting from plastic consumption. According to the Australian Coral Reef Research Center (ACRRC), reefs exposed to plastic waste have about an 89% chance of being affected by diseases, compared to just 4% for reefs not affected by plastic waste. Coral reefs most exposed to plastic wastes appear in Indonesia, which is approximately 26 parts per 100 square meters [13]. Waste management with the theme "3R" (Rescue, Reduce, Recycle) has been considered ineffective.

Several types of plastics commonly used as raw materials are poly-ethylene terephthalate (PET), High-Density Poly-Ethylene (HDPE), Polyvinyl Chloride (PVC), Low-Density Poly-Ethylene (LDPE), Poly Propylene (PP), etc. Among these, PET with the chemical formula (C10H8O4)n, is widely available at landfills as it is used as a raw material for mineral-water bottles. It is also very difficult to decompose. One of the advantages of PET plastic waste is that it can be recycled into various types of goods that have economic value such as clothing, bags, furniture, and carpet. Another use of PET plastic is to convert it to fuel oil via pyrolysis [14]. It has been reported in the literature that PET has moderate to high conversion compared to other plastic wastes such as LDPE and HDPE [14,15]. PET plastic possesses a high calorific value, which makes the conversion process using pyrolysis very effective [16].

Based on the literature, it is necessary to find a technique that reduces the amount of plastic waste, by converting plastic waste into an alternative fuel. Many researchers have investigated techniques that would reduce plastic waste in a short time, which is to convert plastic waste into fuel oil via pyrolysis [17], specifically by heating the polymer material without or using only a little oxygen [18,19]. Pyrolysis is the process of thermo-chemical decomposition of organic compounds through the heating process without or in the presence of only a small amount of oxygen and other chemical reagents [20]. Pyrolysis thermally decomposes long-chain polymer molecules into less complex molecules [21]. Pyrolysis has been chosen by many researchers due to its ability to produce a high oil yield of up to 80 wt.% at a temperature of about 500 ◦C. In many industrial applications, pyrolysis is carried out at atmospheric pressure and operating temperatures above 430 ◦C. Figure 1 shows the chemical reaction of the pyrolysis process. Pyrolysis is divided into three types: hydrocracking, thermal cracking, and catalytic cracking. According to Cleetus et al. [22], PET undergoes pyrolysis that produces different gases i.e., CO2 and CO, and other miscellaneous hydrocarbons. Furthermore, condensation occurring

in the heat-exchange process produces plastic oil with the chemical formula C13.8H23.56 [23]. There are three major products produced during pyrolysis. These are oil, gas, and char, which is valuable for industries, especially production and refineries [24–26].

**Figure 1.** The chemical formula of the pyrolysis process.

Previous research on the pyrolysis of waste plastic oil as has been reported by Ramadhan and Ali [27]. They produced pyrolysis oil from waste LDPE and HDPE at temperatures of 250 ◦C to 420 ◦C and found that oil characteristics are similar to that of diesel fuel. Sarker et al. [28] studied the thermal cracking of waste LDPE under temperatures of 150 ◦C to 420 ◦C without a catalyst and found that the produced oil properties are similar to those of kerosene.

In Indonesia, the fuel vendorship is distributed by state-owned enterprises (Pertamina) throughout the country. Indonesia has several grades for both diesel and gasoline. Gasoline and diesel fuel standards were updated in 2013. Government regulations stipulate that gasoline fuel should maintain the Euro 2 sulfur limit for RON 88, eliminating lead in the fuel. For diesel fuel, the minimum limit for a cetane number of 48 is mandated in government regulations. There are four types of gasoline grades sold in Indonesia, namely Premium (RON88), Pertalite (RON90), Pertamax (RON91), and Pertamax Plus (RON95) [29]. The Ministry of Energy has since 2008 mandated a minimum limit of biofuel volume to be blended into gasoline and diesel fuels [3,30]. This regulation has undergone several updates. The most recent one, released in 2015, set the bioethanol blend in gasoline to be 5% in 2016 and 10% in 2020. In addition, the biodiesel percentage in diesel for the transportation sector was set to be 20% in 2016 and 30% in 2020.

Previous studies have investigated the use of plastic oil as fuel in gasoline engines. One of them was done by Khan et al. Related to the characteristics of WPO–diesel blends, the study obtained a maximum yield of 77.03% within 2 h. Cleetus et al. [22] studied engine performance using WPO–gasoline blends. However, the type of engine used had a low engine speed of about 1500 rpm. It is important to mention that the effect of WPO–gasoline blends on SI engine performance parameters such as engine power, specific fuel consumption (SFC), and thermal efficiency have not been elucidated properly in previous studies. Thus, the objective of this study is to examine the engine performance of two low-RON gasoline (RON 88 and RON90) blended with WPO at varying engine speeds. In doing so, this study also examines the suitability of gasoline–WPO blend fuel for an SI engine as a potential renewable fuel source for future energy supply.

#### **2. Materials and Methods**

#### *2.1. Materials*

Plastic waste was collected from the final disposal site on the coast of Banda Aceh, Indonesia. Then, plastic waste was washed several times and dried under sunlight. After that, the waste was cut into small pieces. The experiments were carried out in the Laboratory of Fuel Engines and Propulsion Systems, Department of Mechanical Engineering, Faculty of Engineering, Syiah Kuala University.

#### *2.2. Production of WPO via Pyrolysis*

Before the beginning of pyrolysis process, it was ensured that the raw materials were washed thoroughly, cut into pieces, and dried under sunlight. The PET pieces were then weighed up to 1 kg. Figure 2 shows a schematic diagram of the pyrolysis process for plastic waste. The main component consists of a reactor chamber and condenser. The condenser was connected to a reactor chamber by an iron pipe exchanger submerged in cold water so that the condensation process ran smoothly. Digital thermocouples Type K, Length 30cm and diameter 5 mm was directly connected to the reactor chamber to monitor the temperature of the plastic waste gas from the pyrolysis process. The preparation was finalized by installing an iron pipe with heat insulation cladding between the reactor and condenser. The pyrolysis process used Liquefied Petroleum Gas (LPG) as a provider of thermal energy. The produced gas flowed into the reservoir through the heat exchanger pipe using a condensation process as a liquid oil. The pyrolysis process began by turning on a reactor that was set at 300 ◦C in a vacuum condition. At the same time, the condenser cooler was supplied. The temperature of the reactor was maintained at 300 ◦C [31] for 2 h 30 min. As the product gases flowed into the condenser, some compounds were condensed. The parts that did not condense remained in the gas phase. The pyrolyzed oil was collected and weighed for analysis. The oil from the plastic waste can be seen in Figure 3. The oil yield from waste plastic through the pyrolysis process at a temperature of 300 ◦C produced a 53.8% (*w*/*w*) yield of WPO. Sample testing was carried out to determine the chemical content of WPO. The yield, i.e., conversion of plastic to oil, was determined using the following equation [32]:

**Figure 2.** Schematic diagram for converting plastic waste to oil via pyrolysis.

**Figure 3.** Pictorial view of produced WPO.
