Characterization of the low temperature chemistry of large hydrocarbons for model development in motor control

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Low-temperature combustion (NTV) can increase the efficiency of engines while reducing their emissions. In NTV a fuel-air mixture that is as homogeneous as possible is produced and burned after self-ignition. The FOR2401 develops approaches for the control of NTV processes that allow engines to be operated transiently and stably in a wide characteristic field. A particular challenge in the control of NTV processes are the cyclic fluctuations across scales caused by the convolution of reaction-kinetic and fluid mechanical effects. Consequently, the concept of the FOR2401 is to develop a multi-scale control. NTV processes can be controlled through controlled multiple injections, intermediate compression, exhaust gas recirculation and water injection. Since ignition and pollutant formation processes are determined by the kinetics of the substances and reactions involved in the process under the conditions set by the control interventions, kinetic questions arise concerning the reaction sequences during the conversion of partially combusted mixture with additional fuel, during ignition and during the formation of pollutants.To investigate these open questions, the conversion of fuel-air mixtures in a flow reactor and a well-stirred reactor is analyzed by mass spectrometry and gas chromatography. By varying the pressure, the reaction temperature, the residence time and the equivalence ratio, data sets are obtained from which conclusions on the reaction pathways can be drawn. Experimentally, pressures of up to 20 bar are realized, in particular to investigate the conditions of intermediate compressions or multiple injections. The work systematically addresses the reaction kinetics of the n-alkanes from n-heptane to n-dodecane, i-octane, toluene and methylcyclohexane, which are surrogate components of diesel or gasoline. Within the FOR2401, the data will be used to improve the reaction mechanism that predicts the reactivity under engine conditions and thus integrates the kinetic principles into the control strategies.In addition, the relationship between ion formation during combustion and the thermodynamic state of the combusted gas mixture will be investigated to determine how the ion current signal, which is comparatively easy to measure in the engine, can be used in combination with the cylinder pressure as a control parameter. For this purpose, low-pressure flames in which the formation of ions is relatively well known are examined first. The investigations are then extended to the NTV parameter range in the high-pressure reactor in order to find formation reactions at these temperatures. The ion formation is ideally captured in as few formation reactions as possible even at low temperatures and moderate pressures and can then be incorporated in to the control strategies in the form of very small reaction mechanisms.