The article presents the results of experimental studies of possible partial replacement of traditional diesel fuel by biofuel. The term biofuel refers to a mixture of diesel fuel with vegetable oils such as palm or peanut oils. The optimal supply of vegetable oils is determining under conditions of preservation or deterioration of diesel engine performance in the range of 5 … 8%. The experiments suppose a diesel engine operation without any interfering within design or regulation of the diesel engine and its fuel equipment. Hydrogen peroxide or kerosene is used to improve the physicochemical properties of vegetable oils. It has been found that under these constraints, the optimal supply of palm oil is 20%. In case of peanut oil, experimentally found that its volume part in biofuel can be increased up to 40%. To provide an equal density and viscosity of the biofuel and the base diesel fuel 30% of diesel fuel were replaced by kerosene. In the range of low and medium engine loads, an emission of main toxic components of nitrogen oxides NOx, emission of solid carbon particles with exhaust gas C, carbon oxides changes insignificantly, and even decreases. The concentration of unburned hydrocarbons is significantly reduced. At engine loads above 50% for peanut oil and 75% for palm oil biofuels, presumably due to worse mixture formation, there is a sharp decrease in nitrogen oxide emissions and an increase in carbon monoxide concentrations.

The high requirements for limiting the toxic components of exhaust gases of modern internal combustion engines require significant expenditures both for the improvement of existing engines and for the development and implementation of new types of engines. Some European organizations are raising the issue of limiting the use of diesel engines and even a possible cessation of their production in the next 5-10 years. This article reflects the results of studies on the formation of one of the most toxic components of exhaust gases - nitrogen oxides. The calculations were carried out according to the thermodynamic cycle model, which makes it possible to estimate the main characteristics of the operating cycle as the fuel-air charge burns out. Calculations are carried out with regards to a gas-diesel modification of an air-cooled engine with a dimension of 120 x 120 mm, which assumes the supply of the main gas-air charge through the inlet pipeline and a limited dose of diesel fuel injected into the cylinder to ignite the charge. The model shows the conditions for the burnout of the charge and the formation of nitrogen oxides in 10 equal in mass and successively burnout zones of the charge in the diesel cylinder. Calculations show that the formation of nitrogen oxides can be significantly reduced by 50 … 80% by adjusting the charge stratification scheme, that is, by changing the fuel concentration in the burnt-out portions, due to the mutual regulation of diesel and gas fuel supplies. The results of experimental verification of the calculations are presented below, which confirms the adequacy of the model. The effect in the total reduction of NOx emissions can be significantly improved by using partial charge throttling and using exhaust gas recirculation. The data obtained confirm the feasibility of further fine-tuning the working process of gas-diesel engine modifications and meeting the requirements of toxicity standards.

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The authors showed that the European Union norms for the toxicity of exhaust gases (Euro 1 – Euro 5) contributed to the reduction of main harmful components emissions by several times. In foreign countries, Stage and Tier regulations applied to tractor equipment, which also limited the content of toxic components at the legislative level.(Research purpose) To reduce the content of nitrogen oxides in exhaust gases by more efficient regulation of the fuel charge distribution in the gas-diesel engine cylinder, changes in the concentration of diesel and gas fuel in certain zones, as well as the use of exhaust gas recirculation.(Materials and methods) The authors analyzed the results of modeling the formation of nitrogen oxides by controlling the workflow in the gas-diesel modification of the diesel engine. In the calculations, the geometric parameters of the D-120 engine, operating at 2000 revolutions per minute, with a filling of 0.6-0.9 volume, were used. The average excess air ratio for the charge was 1.2-3.0, and the excess air ratios for the gas-air mixtures did not exceed 1.2-2.5.(Results and discussion) Using the computational model, the authors estimated the parameters at different pressures at the engine inlet within 0.05-0.09 megapascals, as well as with an increase in the residual gas coefficient in the range of 5-15 percent with a decrease in the concentration of nitrogen oxides from 2500 to 1100 parts per million. Experiments showed that when the power changed from 100 to 20 percent, the nitrogen oxides concentration decreased from 1940 to 800 parts per million.(Conclusions) The authors confirmed the adequacy of the calculation model. They determined that a 40-50 percent reduction in the nitrogen oxide concentration in exhaust gases was achieved with various layering schemes in the combustion chamber. They found that the standards for carbon monoxide, hydrocarbons and nitrogen oxides would require mixed engine regulation. It was proved that recirculation of 15 percent of exhaust gases could reduce nitrogen oxide emissions by another 50 percent.