Evaluation of the biological methane potential of various feedstock for the production of biogas to supply agricultural tractors

Highlights: • Biochemical methane potential for mixtures of whey, manures and silages was tested. • High impact of feedstock type on composition and yield of biogas was observed. • Simple mathematical model of methanogenic fermentation was proposed. • Exhaust emissions from dual fuel (biogas and diesel oil) engine were investigated. • Using biogas in engine reduces particulate matter and nitrogen oxides emissions. - Abstract: This work is divided into three parts. The first one presents results of biological methane potential of agriculture raw materials available in Poland. In the second part the simple mathematical model of methanogenic fermentation is proposed. The data for this model were obtained from experimental digestion process of chosen mixtures. Last part includes the results of research of exhaust emissions generated by dual dual-fuel engine of agricultural tractor powered by mixture of model biogas (60% and 70% of methane) and diesel oil. The obtained results revealed that there was a significant difference in chemical composition and yield of biogas between considered feedstock types. The highest biogas and methane production was obtained for mixtures in ratio of 6:4 for swine manure/maize silage and whey/grass silage. Due to agriculture conditions in Poland and obtain results, the maize silage and swine manure were chosen to development of mathematical model of fermentation process. It showed a satisfactory match to the experimental results. Results of emission tests on dual-fuel tractor engine supplied with biogas and diesel oil showed the higher concentrations of hydrocarbons and carbon oxide and lower concentrations of particulate matter in exhaust gases. Level of emission of particular components depends on the biogas composition.