## 1 Introduction  
Liquid alternative fuels are substances used to replace traditional fuels such as gasoline and diesel, usually to reduce greenhouse gas emissions and dependence on fossil fuels. Biofuels are often classified by generation, which refers to how the raw materials are produced and the production processes. There are typically three main generations of biofuels [1, 2]. First-generation biofuels are produced from readily available plant feedstocks, such as corn, sugar cane, rapeseed, or palm oil. The production process for first-generation biofuels is relatively simple and usually involves fermentation or extraction of vegetable oil. However, their production can compete with food production, leading to land-use conflicts [3, 4, 5]. Second-generation biofuels are produced from non-food feedstocks, such as plant residues, stems, leaves, straw, or organic waste. Second-generation biofuel production processes are more technologically advanced and typically involve chemical, thermal, or biological processes, such as biomass thermochemical conversion or cellulose fermentation. Second-generation biofuels may have less impact on food production and may be more environmentally sustainable [6, 7, 8, 9]. Third-generation biofuels include biofuels produced from algae, bacteria, or other microorganisms. These microorganisms can be grown in special reactors and used to produce biofuels such as biodiesel or biomethane. Third-generationbiofuels have higher production potential than crops and can be produced on land unsuitable for traditional agriculture. However, third-generation biofuel production technologies are still in the development and commercialization phases [10; 11; 12].  
As technology advances, more emphasis is being placed on developing second and third-generation biofuels due to their potential to reduce greenhouse gas emissions and have less impact on food production [1; 13; 14; 15]. Such fuels include hydrotreated diesel. HVO fuel is a biofuel produced from vegetable oils or animal fats using hydrovet. This process involves subjecting the oil or fat to high temperatures and pressures in the presence of hydrogen and a catalyst, leading to hydrotreating, which removes oxygen from the oil or fat molecules [16; 17; 18; 19]. HVO fuel is considered a clean fuel because its production eliminates impurities such as sulfur, nitrogen, and aromatic compounds in traditional diesel fuels [20; 21]. As a result, HVO can potentially reduce emissions of atmospheric pollutants and greenhouse gases compared to conventional diesel. In addition, HVO fuel complies with diesel fuel quality standards, which means it can be used without modifying engines or infrastructure [22; 23; 24; 25]. The main motivation for performing empirical tests on an engine dynamometer using HVO fuel was the search for alternative power sources for internal combustion engines. Because HVO fuel is often promoted as a more sustainable alternative to traditional fuels, the authors of this article decided to look more closely into the subject of this fuel. This was the first research of its kind using HVO fuel conducted at the Warsaw University of Technology. HVO fuel is becoming increasingly popular in many countries, including some in Europe, due to its environmental benefits and ability to replace traditional diesel fuel in various sectors, including road, marine, and air transport.