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Aerodynamic Optimization of the High Pressure Turbine and Interstage Duct in a Two-Stage Air System for a Heavy-Duty Diesel Engine

[+] Author and Article Information
Uswah B. Khairuddin

Department of Mechanical Engineering Imperial College London South Kensington Campus London SW7 2AZ United Kingdom
u.khairuddin13@imperial.ac.uk

Aaron W. Costall

Department of Mechanical Engineering Imperial College London South Kensington Campus London SW7 2AZ United Kingdom
a.costall@imperial.ac.uk

1Corresponding author.

ASME doi:10.1115/1.4038024 History: Received June 30, 2017; Revised August 05, 2017

Abstract

Turbochargers reduce fuel consumption and CO2 emissions from heavy-duty internal combustion engines by enabling downsizing and downspeeding through greater power density. This in turn raises turbine expansion ratio levels, leading to air systems with multiple stages and a need for interconnecting ducting, all subject to tight packaging constraints. This paper considers the aerodynamic optimization of the exhaust side of a two-stage air system for a Caterpillar 4.4-litre heavy-duty diesel engine, focusing on the high pressure turbine wheel and interstage duct. Using current production designs as a baseline, a genetic algorithm-based aerodynamic optimization process was carried out separately for the wheel and duct components in order to minimize the computational effort required to evaluate seven key operating points. While efficiency was a clear choice of cost function for turbine wheel optimization, different objectives were explored for interstage duct optimization to assess their impact. Optimization designs depended strongly on the engine operating point and so each case was evaluated at every other engine operating point, to determine the most appropriate designs to carry forward. Prototypes of the best compromise high pressure turbine wheel and interstage duct designs were manufactured and tested against baseline designs to validate CFD predictions. The best performing high pressure turbine design was predicted to show an efficiency improvement of 2.15 percentage points, for on-design operation. Meanwhile, the optimized interstage duct contributed a 0.2 and 0.5 percentage-point efficiency increase for the high and low pressure turbines, respectively.

Copyright (c) 2017 by ASME
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