Changing regulations on emissions from propulsion sources used in transportation and closed-loop resource management are intensifying the search for substitute fuels especially for compression-ignition engines. In the study, three fuels were tested for comparison: conventional diesel fuel (DF), hydrotreated vegetable oil (HVO), and a mixture of HVO with waste pyrolytic oils from polypropylene (PPO) and polypropylene (PSO) in 60/20/20 weight ratios (HVO+WPPO). Tests were conducted on a specialized platform with an AVL 5402 engine, analyzing their combustion and operating stability under two different load and speed conditions. The results showed that HVO and the HVO+WPPO mixture exhibit similar or even better combustion performance compared to DF. Some differences were found in cylinder pressure traces, indicated mean effective pressure and heat release. Statistical analyses, including ANOVA and Levene's tests, confirmed significant differences between the fuels, indicating the potential of the HVO+WPPO mixture as an environmentally friendly alternative. The determined coefficients of variation allowed an assessment of the stability of engine operation. In conclusion, the research suggests that both HVO and its mixture with PPO and PSO can be effective and environmentally friendly solutions for diesel engines, with the possibility of wide application in the future.