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Numerical Modelling of the Flow in Micro- Turbine of Organic Rankine Cycle (ORC) on Internal Combustion Engine (ICE) Waste Heat

Both the increase in the cost of energy during the past decades and many environmental problems caused by fossil fuel consumption lead that energy savings have been of great importance. In internal combustion engine (ICE) the chemical energy of the fuel is converted into heat through combustion. By some of the thermodynamic cycles, part of heat energy is converted into useful mechanical work. The remaining heat energy is realised into the environment as the waste heat generated from exhaust gas and cooling water. So, ICE typically has a thermodynamic efficiency in the range of 20 to 50%. On the other hand, there is proven, commercially available technology to convert part of the waste heat into electricity. This is Organic Rankine Cycle (ORC), used since several decades in geothermal power plants. Applications of this technology for waste heat recovery are rather premature. The exhaust gases have a temperature in the range 300 oC – 400 oC and thus are very suitable as heat source for an ORC system. Also the jacket cooling water, with temperatures between 80 oC – 90 oC, also can be integrated in ORC system. On this manner the total efficiency of the combined system (ICE and ORC) can be substantially improved. In this paper, energy analysis with aim to improve the recovery of the waste heat of an ICE with Organic Rankine Bottoming Cycle (ORBC) is presented. Considering characteristics of the waste heat of exhaust gas and cooling water, a combined cycle for waste heat recovery of ICE is proposed. The thermodynamic analysis show that in case biogas ICE of 555 kW power a 9.2% increase in the overall power and 3.7% increase in the overall thermodynamic efficiency can be achieved with respect to the engine with no bottoming with ORC. In this paper, special attention is paid to the design of micro- turbine for ORC. It is the innovative axial, action and multistage turbine of effictive power of 57 kW. By using the analytical method a new (non-standard) profiles for stator and rotor blades are designed. The convex and concave sides of the profiles are designed by a polynomials of the fifth degree. Because of achieving high isentropic efficiency of the turbine, the aerodynamic characteristics of the new designed profiles are improved by optimizing their geometry on the basis of numerical modelling of flow in the stator and rotor cascades.

Numerical Modelling ; Flow ; Micro-Turbine ; Organic Rankine Cycle (ORC) ; Internal Combustion Engine (ICE) ; Waste Heat

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