clean technologies Article Impact of Pyrolysis Oil Addition to Ethanol on Combustion in the Internal Combustion Spark Ignition Engine Magdalena Szwaja 1 , Mariusz Chwist 1 , Stanislaw Szwaja 1, * and Romualdas Jukneleviˇ cius 2   Citation: Szwaja, M.; Chwist, M.; Szwaja, S.; Jukneleviˇ cius, R. Impact of Pyrolysis Oil Addition to Ethanol on Combustion in the Internal Combustion Spark Ignition Engine. Clean Technol. 2021, 3, 450–461. https://doi.org/10.3390/ cleantechnol3020026 Academic Editor: Leonid Tartakovsky Received: 19 March 2021 Accepted: 28 April 2021 Published: 26 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Faculty of Mechanical Engineering and Computer Science, Czestochowa University of Technology, 21 Armii Krajowej St., 42-200 Czestochowa, Poland; magdaszw24@gmail.com (M.S.); mariusz.chwist@op.pl (M.C.) 2 Faculty of Mechanics, Vilnius Gediminas Technical University, J. Basanavicius str. 28, 03224 Vilnius, Lithuania; romualdas.juknelevicius@vgtu.lt * Correspondence: szwaja@imc.pcz.pl; Tel.: +48-885-840-483 Abstract: Thermal processing (torrefaction, pyrolysis, and gasification), as a technology can provide environmentally friendly use of plastic waste. However, it faces a problem with respect to its by- products. Pyrolysis oil obtained using this technology is seen as a substance that is extremely harmful for living creatures and that needs to be neutralized. Due to its relatively high calorific value, it can be considered as a potential fuel for internal combustion spark-ignition engines. In order make the combustion process effective, pyrolysis oil is blended with ethanol, which is commonly used as a fuel for flexible fuel cars. This article presents results from combustion tests conducted on a single-cylinder research engine at full load working at 600 rpm at a compression ratio of 9.5:1, and an equivalence ratio of 1. The analysis showed improvements in combustion and engine performance. It was found that, due to the higher calorific value of the blend, the engine possessed a higher indicated mean effective pressure. It was also found that optimal spark timing for this ethanol-pyrolysis oil blend was improved at a crank angle of 2–3 ◦ at 600 rpm. In summary, ethanol-pyrolysis oil blends at a volumetric ratio of 3:1 (25% pyrolysis oil) can successfully substitute ethanol in spark-ignition engines, particularly for vehicles with flexible fuel type. Keywords: pyrolysis oil; ethanol; combustion; spark ignition engine 1. Introduction Pyrolysis oil (PO) is a black, liquid substance obtained from the thermal processing of organic substances at temperatures of 350–600 ◦ C in the absence of oxygen. This thermal process is known as pyrolysis. It is considered the most effective technology for the subsequent utilization of used tires, as well as other organic compounds. As a result of this process, three products are generated: carbon-rich char, gases, and hydrocarbon vapors, which condense to liquids when cooled to ambient temperatures. The liquids can be treated as alternative fuels; hence, they can be burned in internal combustion engines. Thermal processing technologies—including torrefaction, pyrolysis, and gasification—are commonly used for biomass processing, with a focus on the production of charcoal and syngas, which can be used as alternative fuels. The amount of both producer gas and charcoal depends on the following: the input feedstock, the process temperature, and the retention time of the feedstock inside a pyrolysis reactor. In addition, the physicochemical properties of the liquid fuel obtained from the pyrolysis process also vary depending on the feedstock [1–4]. Furthermore, at various process temperatures (350–600 ◦ C), the ratio of char, oil and syngas also vary. Table 1 shows the percentage of gaseous, liquid, and solid products from pyrolysis in plants presented in papers [5–8]. The quality of the pyrolysis oil depends on its further processing. To that end, dis- tillation is applied to obtain physical and chemical properties like those of diesel fuel [9]. Vihar et al. [9] found that their pyrolysis oil was more viscous than diesel fuel. As stated Clean Technol. 2021, 3, 450–461. https://doi.org/10.3390/cleantechnol3020026 https://www.mdpi.com/journal/cleantechnol