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Abstract. Th e expansion of production and the use of biofuels are determined by the legal acts of the European Commission and National legal acts encouraging such production and usage. It would be meaningful to use the mixtures of butanol and petrol in Otto engines. It was determined the possibility of producing biobutanol as a biofuel of the second generation from lignocellulose hydrolyzed to C 5 /C 6 carbohydrates. If the 20-30% potential of lignocellulose biomass in Lithuania is used, it would be possible to produce 200-300 thousand t of biobutanol per year. Th e amount of carbon monoxide CO decreases by more than 80% when the engine works using the mixtures of petrol and butanol if compared to the CO amount of the engine working with petrol. When the engine works using the mixture of 30% butanol and petrol, the amount of carbon dioxide CO 2 decreases by 4% on average, and in case it works with the mixture of 50% butanol and petrol -by 14% if compared to the CO 2 amount of the engine working using petrol. When the engine works using the mixture of 30% butanol and petrol, the amount of hydrocarbons HC decreases by 26% on average, and if it works with the mixture of 50% butanol and petrol, the amount increases by some 4% if compared to the HC amount of the engine working using petrol. To generalize the results of the performed experiment, it is possible to state that the optimal mixture would consist of 70% petrol and 30% biobutanol.

This paper presents a study on the energy efficiency and emissions of a converted high-revolution bore 79.5 mm/stroke 95 mm engine with a conventional fuel injection system for operation with dual fuel feed: diesel (D) and natural gas (NG). The part of NG energy increase in the dual fuel is related to a significant deterioration in energy efficiency (ηi), particularly when engine operation is in low load modes and was determined to be below 40% of maximum continuous rating. The effectiveness of the D injection timing optimisation was established in high engine load modes within the range of a co-combustion ratio of NG ≤ 0.4: with an increase in ηi, compared to D, the emissions of NOx+ HC decreased by 15% to 25%, while those of CO2 decreased by 8% to 16%; the six-fold CO emission increase, up to 6 g/kWh, was unregulated. By referencing the indicated process characteristics of the established NG phase elongation in the expansion stroke, the combustion time increase as well as the associated decrease in the cylinder excess air ratio (α) are possible reasons for the increase in the incomplete combustion product emission.

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The global policy solution seeks to reduce the usage of fossil fuels and greenhouse gas (GHG) emissions, and biogas (BG) represents a solutions to these problems. The use of biogas could help cope with increased amounts of waste and reduce usage of fossil fuels. Biogas could be used in compressed natural gas (CNG) engines, but the engine electronic control unit (ECU) needs to be modified. In this research, a spark ignition (SI) engine was tested for mixtures of biogas and hydrogen (volumetric hydrogen concentration of 0, 14, 24, 33, and 43%). In all experiments, two cases of spark timing (ST) were used: the first for an optimal mixture and the second for CNG. The results show that hydrogen increases combustion quality and reduces incomplete combustion products. Because of BG’s lower burning speed, the advanced ST increased brake thermal efficiency (BTE) by 4.3% when the engine was running on biogas. Adding 14 vol% of hydrogen (H2) increases the burning speed of the mixture and enhances BTE by 2.6% at spark timing optimal for CNG (CNG ST) and 0.6% at the optimal mixture ST (mixture ST). Analyses of the rate of heat release (ROHR), temperature, and pressure increase in the cylinder were carried out using utility BURN in AVL BOOST software.