This paper highlights the results of scientific research on the possibility of increasing the biofuel concentration in the fuel used in diesel engines by introducing bioethanol in multicomponent diesel fuel mixtures containing fossil diesel fuel (D), rapeseed oil methyl esters (RME), and ethanol (E). In the initial stage of the research, we performed an analysis of the physicochemical parameters of fuel and comparative tests of a diesel engine running on pure fossil diesel fuel, rapeseed oil methyl esters (RME), and RME-E mixtures. In engine test:, it has been shown that increasing the ethanol amount in biodiesel fuel up to 40% leads to an increase in indicator index eta(i) of the tested diesel engine 1 A41 by 2.5%. CO and NOx emissions decreased up to 10-12% for every 10% increase of ethanol amount in blend with rapeseed oil methyl esters, The influence of different levels of ethanol on CO and NOx, emissions from fuel and on experimentally defined dynamics of the indicator process can show alternative improvements of the performance characteristics of the diesel engine while working on fuel mixtures.