Browse Publications Technical Papers 2019-01-0964
2019-04-02

Reforming-Controlled Compression Ignition – a method combining benefits of ‎Reactivity-Controlled Compression Ignition and High-Pressure Thermochemical ‎Recuperation 2019-01-0964

This work investigates a new method enabling full HCCI engine control based on a ‎combination of Reactivity-Controlled Compression Ignition and High-Pressure ‎Thermochemical Recuperation, while the engine is fed with a single primary fuel. ‎ Basically, the primary fuel and water flow through a heat exchanger and a reformer ‎heated with the exhaust gases, where they evaporate and then react for creating a ‎hydrogen-rich reformate. The reformate composition depends on the primary fuel and ‎the reformer design (catalyst, geometry, etc.), and contains some other species in ‎addition to hydrogen. Various primary fuels are suitable for the suggested concept. In ‎the reported study, the primary fuel is dimethyl ether (DME), and the reformer is ‎designed to produce mainly hydrogen, carbon dioxide, carbon monoxide, and water. The ‎applied reforming process is steam reforming of DME supported by a bi-functional ‎‎(metal and acid) catalyst. Both DME (high-reactivity fuel) and the ‎reformate (low-‎reactivity fuel) are injected directly but separately into the cylinder. Combustion control ‎is achieved by changing the reactivity/composition of the total fuel supplied into the ‎cylinder. This method enables adequate combustion control in the entire range of ‎operating modes, including transients, due to the separate DME and reformate injection.‎ This work presents results of 1D and 3D CFD simulations. The 1D model includes the ‎whole engine-reformer system and is mainly intended for energy balance and reformer ‎reaction rate calculations. The 3D model is aimed at the combustion process prediction. ‎A reduced chemistry mechanism is applied. The prediction results show system ‎efficiency improvement up to six percentage points as compared to HCCI engine ‎without High-Pressure Thermochemical Recuperation, while the improvement is higher ‎in naturally low-efficiency regimes. At all considered operating modes a shortage in ‎available enthalpy for the reforming is not observed. Suitability of different injection ‎methods to decrease ringing intensity, and hence to expand the high-load operation ‎limit, is investigated.‎

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