Exergetic analysis of reactive systems for polygeneration

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This subproject designs process concepts for the use of fuel-rich HCCI engines for the polygeneration of work, heat, and useful chemicals and evaluates them thermodynamically and exergoeconomically. As before, the focus with regard to useful chemicals will be on synthesis gas and higher-value hydrocarbons such as ethyne and ethene. Due to the slow auto-ignition of methane/air mixtures, additives and preheating of the fresh gas by means of exhaust gas recirculation or recuperation plays an important role. In the preceding project period, the positive effects of reactive additives such as n-heptane and dimethyl ether were demonstrated. These are mainly due to the reduction of the inlet temperature required for methane ignition in HCCI engines. However, a substantial part of the energy and carbon is introduced by the additive. Therefore, alternative additives, such as ozone, are interesting, that are active at much lower concentration. These will now be investigated in the proposed project period. In preliminary studies it was exemplarily shown that very small amounts of ozone enable ignition at reduced temperature even in the fuel-rich range.Therefore, it is now aimed to quantify the engine kinetics and thermodynamics of methane and ethanol mixtures with ozone in the fuel-rich range by means of simulations. On the one hand, it is necessary to uncover correlations between ozone quantity, reactive intermediates and end products for the fuel-rich range in compression-expansion cycles. On the other hand, the aim is to find realistic parameter ranges for engine polygeneration also with regard to pressure rise rates and combustion phasing. Finally, the quality of the engine process, also in cooperation with the experimental subprojects, is to be evaluated by means of the exergy concept, in order to reduce irreversibilities.Since the engine process can only be regarded as a subsystem, conclusions about its thermodynamic quality are important, but must also be considered together with upstream and downstream process steps, both applying thermodynamic and economic considerations. Whether engine polygeneration will be used, depends ultimately on the total costs and the value of the energy and chemical products compared to competing conversion methods. The exergo-economic consideration of the costs of exergy destruction and the investment costs provides important information about possibilities for improvement. So far, it has been established that the engine-based polygeneration process is also thermodynamically and economically advantageous as an overall system, but weak points have also been uncovered. The aim of this project is to develop process concepts including material separation and energy integration for promising motor conditions with ozone addition and to evaluate them in comparison to alternative concepts.