Session: 19-01: Turbines and Energy recovery.

Submission Number: 177999

Design and Analysis of Small-Scale ORC Turbines for Waste Heat Conversion From an Heavy- Duty Internal Combustion Engine 

Organic Rankine bottoming cycles are an efficient option to maximize the fuel energy conversion into mechanical power with thermal engines. Within a research project aiming at optimizing the performance of an ethanol-fuelled spark ignition engine, the authors are carrying out studies for the optimal selection of the characteristics of an ORC expander for the final conversion of the residual heat contents in the exhausts. The engine being of the heavy-duty type with a total displacement of 9l, the expander is characterized by design data that fall inside the allowable range of high-speed radial inflow turbines. Furthermore, the engine - ORC turbine matching leads not only to performance optimization but also to high flexibility when complying with variable energy demands from final users.

In this paper, the authors develop a particular design strategy whose purpose is both the definition of optimal geometrical and operating features of the turbine and the identification of the more appropriate organic fluid for this particular application. The authors’ method mainly founds on an extension of similarity criteria, which allows geometrically similar stator-rotor systems to be considered by using an appropriate scaling factor according to the working fluid. More specifically, the typical turbomachinery similarity indices, say specific speed and diameter and flow and load coefficients as well, do not provide enough information to transfer the design concepts from a baseline fluid to a different one. For this reason, based on the current scientific literature in this topic, the authors have integrated the optimal search of the turbine features with two additional parameters i.e., the inflow / outflow density ratio and the isentropic Mach number. The first one, if matched, allows the same typical flow area ratios to be preserved, while the second one suggests the use of either subsonic or transonic stationary and rotating passages.

The above assumptions are checked, in this paper, by CFD based test cases with different organic fluids that differ one from each other in terms of maximum allowable temperature, molecular weight and structure. The numerical workflow includes an automatic mesh adaptation of the computational domain for the estimation of the unsteady stator – rotor interaction. The results are therefore analyzed not only in terms of overall turbine performance and typical flow distributions, but also with the purpose of identifying flow and pressure fluctuations that may result in time-dependent stresses and aerodynamic noise.

Presenting Author: Roberta De Robbio University of Naples Federico II

Presenting Author Biography: Master’s degree in Mechanical Engineering for Energy and Environment and PhD in Industrial Engineering at University of Naples “Federico II”.
Previously Fellow Researcher at the Institute of Science and Technology in Energy and Sustainable Mobility (STEMS) of the National Council of Research (CNR).
Currently, Assistant Professor at University of Naples “Federico II”.

Studies CFD analysis in internal combustion engines and gas turbines, alternative fuels and renewable energy sources.

Authors:

Roberta De Robbio University of Naples Federico II
Raffaele Tuccillo University of Naples Federico II
Maria Cristina Cameretti University of Naples Federico II