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Currently, one of the major trends in the research of contemporary combustion engines involves the potential use of alternative fuels. Considerable attention has been devoted to methane, which is the main component of Natural Gas (NG) and can also be obtained by purification of biogas. In compression-ignition engines fired with methane or Compressed Natural Gas (CNG), it is necessary to apply a dual-fuel feeding system. This paper presents the effect of the proportion of CNG in a fuel dose on the process of combustion. The recorded time series of pressure in a combustion chamber was used to determine the repeatability of the combustion process and the change of fuel compression-ignition delay in the combustion chamber. It has been showed that NG does not burn completely in a dual-fuel engine. The best conditions for combustion are ensured with higher concentrations of gaseous fuel. NG ignition does not take place simultaneously with diesel oil ignition. Moreover, if a divided dose of diesel is injected, NG ignition probably takes place at two points, as diesel oil.

The pursuit of reduced greenhouse gas emissions, as well as the increased share of renewable fuels in the overall energy balance has led to a search for alternative energy sources. One of the fuels on which great hopes are set as fuel for engines is biomethane or biogas, whose main component is methane. Biogas can be obtained from different products by using different technologies, so that it has potential as a widelyavailable fuel, which is quite easy to produce. The percentage of methane in biogas depends on the technology for obtaining biogas and ranges from 35% to around 75%. The largest biogas sources can be animal farms, where it is obtained from animal excrement. Another source is sewage treatment plants and rubbish dumps, where substantial quantities of biogas are obtained as a result of natural processes occurring in waste dumping sites or sewage. Biogas can also be acquired from waste obtained from fruit and vegetable processing as well as waste from meat plants. This paper examines the possibility of using biogas as a fuel for diesel engines. In these engines, the combustion of biogas (methane) requires the application of a dual-fuel supply system in which liquid fuel initiating gas fuel selfignition will be injected into the combustion chamber along with methane. The paper also contains example results showing the effect of the methane dose on the course of the combustion process in diesel engines.

Protection of the environment and counteracting global warming require finding alternative sources of energy. One of the methods of generating energy from environmentally friendly sources is increasing the share of gaseous fuels in the total energy balance. The use of these fuels in compression-ignition (CI) engines is difficult due to their relatively high autoignition temperature. One solution for using these fuels in CI engines is operating in a dualfuel mode, where the air and gas mixture is ignited with a liquid fuel dose. In this method, a series of relatively complex chemical processes occur in the engine's combustion chamber, related to the combustion of individual fuel fractions that interact with one another. Analysis of combustion of specific fuels in this type of fuel injection to the engine is difficult due to the fact that combustion of both fuel fractions takes place simultaneously. Simulation experiments can be used to analyse the impact of diesel fuel combustion on gaseous fuel combustion. In this paper, we discuss the results of simulation tests of combustion, based on the proprietary multiphase model of a dual-fuel engine. The results obtained from the simulation allow for analysis of the combustion process of individual fuels separately, which expands the knowledge obtained from experimental tests on the engine.