The increasing stringency of environmental legislation is encouraging the development of combustion concepts with minimal impact on environment and very low emissions. One of the main strategies to achieve this is the recirculation of combustion products. In addition to reduction of oxygen content within the oxidant and increase in specific heat capacity of the mixture, the recirculation of combustion products introduces also trace amounts of active compounds into the process, including NO2. The aim of this thesis is to experimentally investigate the influence of NO2 presence on the combustion of natural gas. The measurements were carried out in a spark-ignition engine with a homogeneous mixture at engine speed of 1500 min-1, torque of 25 Nm and 100 Nm and normalized air-fuel ratios of 1,4; 1 and 0,85. In each operating point, primary combustion air was doped with four different concentrations of NO2, ranging from 30 ppm to over 400 ppm. Based on the exhaust gas composition measurements, a sensitivity analysis of the combustion process to NO2 addition was performed and the kinetic effects of NO2 were analysed. It turns out that NO2 can act as an ignition promoter under lower temperature conditions due to the faster formation of OH radicals, leading to an acceleration of oxidation reaction rates and thus a faster attainment of the equilibrium state, while also affecting the composition of the exhaust gases.
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