Steady State Engine Test Demonstration of Performance Improvement With an Advanced Turbocharger

Heavy EGR required on diesel engines for future emission regulation compliance has posed a big challenge to conventional turbocharger technology for high efficiency and wide operation range. This study, as part of the U.S. Department of Energy sponsored research program, is focused on advanced turbocharger technologies that can improve turbocharger efficiency on customer driving cycles while extending the operation range significantly, compared to a production turbocharger. The production turbocharger for a medium-duty truck application was selected as a donor turbo. Design optimizations were focused on the compressor impeller and turbine wheel. On the compressor side, advanced impeller design with arbitrary surface can improve the efficiency and surge margin at low end while extending the flow capacity, while a so-called active casing treatment can provide additional operation range extension without compromising compressor efficiency. On the turbine side, mixed flow turbine technology was revisited with renewed interest due to its performance characteristics, i.e. high efficiency at low-speed ratio, relative to the base conventional radial flow turbine, which is relevant to heavy EGR operation for future diesel applications. The engine dynamometer test shows that the advanced turbocharger technology enables over 3% BSFC improvement at part-load as well as full-load condition, in addition to an increase in rated power. The performance improvement demonstrated on engine dynamometer seems to be more than what would typically be translated from the turbocharger flow bench data, indicating that mixed flow turbine may provide additional performance benefits under pulsed exhaust flow on an internal combustion engine and in the low-speed ratio areas that are typically not covered by steady state flow bench tests.

Optimization of a Centrifugal Compressor Impeller Design for Robustness to Manufacturing Uncertainties

Compressor impellers for mass-market turbochargers are die-casted and machined with an aim to achieve high dimensional accuracy and acquire specific performance. However, manufacturing uncertainties result in dimensional deviations causing incompatible operational performance and assembly errors. Process capability limitations of the manufacturer can cause an increase in part rejections, resulting in high production cost. This paper presents a study on a centrifugal impeller with focus on the conceptual design phase to obtain a turbomachine that is robust to manufacturing uncertainties. The impeller has been parameterized and evaluated using a commercial computational fluid dynamics (CFD) solver. Considering the computational cost of CFD, a surrogate model has been prepared for the impeller by response surface methodology (RSM) using space-filling Latin hypercube designs. A sensitivity analysis has been performed initially to identify the critical geometric parameters which influence the performance mainly. Sensitivity analysis is followed by the uncertainty propagation and quantification using the surrogate model based Monte Carlo simulation. Finally a robust design optimization has been carried out using a stochastic optimization algorithm leading to a robust impeller design for which the performance is relatively insensitive to variability in geometry without reducing the sources of inherent variation i.e. the manufacturing noise.

A Comparative Assessment of Dry Gas Turbine Cycles for Marine Applications

This paper presents a comparative assessment of different gas turbine open ‘dry’ cycle configurations as potential prime movers for marine commercial applications. The analyses will focus on optimising a three-spool gas turbine —featuring intercooling, reheating, and/or recuperation— for maximum thermal efficiency at design point, under the premise that targeted marine applications spend most of the time at cruising, hence part-load performance of the power plant will not play a huge role. The most promising configuration will be identified, and a whole methodology of systematic design-space exploration will be established, as the first necessary steps in the context of a much broader project, with the final aim of applying the same methodology to a wider range of candidate gas-turbine based power plants and performing multi-disciplinary optimisation of these candidates to fully assess the capabilities of the gas turbines to enter the market of the large cargo ships.

Evaluation of Axial Compressor Characteristics Under Overspray Condition

An axial compressor was developed for an industrial gas turbine equipped with a water atomization cooling (WAC) system, which is a kind of inlet fogging technique with overspray. The compressor performance was evaluated using a 40MW-class test facility for the advanced humid air turbine system. A prediction method to estimate the effect of WAC was developed for the design of the compressor. The method was based on a streamline curvature (SLC) method implementing a droplet evaporation model. Four test runs with WAC have been conducted since February 2012. The maximum water mass flow rate was 1.2% of the inlet mass flow rate at the 4th test run, while the design value was 2.0%. The results showed that the WAC decreased the inlet and outlet temperatures compared with the DRY (no fogging) case. These decreases changed the matching point of the gas turbine, and increased the mass flow rate and the pressure ratio by 1.8% and 1.1%, respectively. Since prediction results agreed with the results of the test run qualitatively, the compressor performance improvement by WAC was confirmed both experimentally and analytically. The test run with the design water mass flow rate is going to be conducted in the near future.

Conversion of the AE 1107C From the V-22 Osprey Application to Marine Service

This paper presents a study on the conversion of the Rolls-Royce AE 1107C V-22 Osprey gas turbine engine into the MT7 Ship-to-Shore Connector (SSC) marine gas turbine engine. The US Navy led SSC design requires a propulsion and lift gas turbine rated at 5,230 shaft horsepower, which the AE 1107C variant MT7 is capable of providing with margin on power and specific fuel consumption. The MT7 leverages the AE family of engines to provide a propulsion and lift engine solution for the SSC craft. Extensive testing and analysis completed during the AE 1107C development program aided in the robust gas turbine design required to meet the needs of the SSC program. Requirements not met by the AE 1107C configuration were achieved with designs based on the AE family of engines and marine grade sub-system designs. Despite the fact that system integration and testing remain as key activities for integrating the MT7 with the SSC craft, conversion of the AE 1107C FAA certified engine into an American Bureau of Shipping Naval Vessel Rules Type Approved MT7 engine provides a low technical risk alternative for the demanding requirements of the SSC application.

Extreme Temperature Coatings for Future Gas Turbine Engines

The National Energy Technology Laboratory-Regional University Alliance (NETL-RUA) has been developing extreme temperature coating systems that consist of a diffusion barrier coating (DBC), a low-cost wet slurry bond coat, a commercial yttria stabilized zirconia (YSZ) thermal barrier coating (TBC), and an extreme temperature external coating that are deposited along the surface of nickel-based superalloys and single crystal metal substrates. Thermal cyclic testing of these multi-layer coatings was conducted in steam-containing environments at temperatures ranging between 1100–1550°C. This paper discusses the response of these materials during bench-scale testing, and their potential use in advanced H- and J-class land-based gas turbine engines.

Siemens SGT-800 Industrial Gas Turbine Enhanced to 50 MW: Turbine Design Modifications, Validation and Operation Experience

Siemens Oil & Gas introduced an enhanced SGT-800 gas turbine during 2010. The new power rating is 50.5 MW with a 38.3 % electrical efficiency (ISO) in simple cycle and the best in class combined-cycle performance of more than 55 %. The increased power and improved efficiency from the existing 47 MW rating are mainly obtained by improved compressor airfoil profiles and improved turbine aerodynamics and cooling air layout. The upgrade components in the gas turbine are interchangeable from the existing rating. The current paper is focused on the design modifications of the turbine parts and their validation and operation experience. For the turbine section, the main design modifications include the redesigned stage 1 with better aerodynamic and cooling performance, modified stage 3 for increased outlet area, etc. However, the turbine inlet temperature is not increased compared to the existing 47 MW rating. Comprehensive validation measures have been taken to make sure that the modifications meet the design targets, at both the component level and the system level. The results from the validation tests have confirmed the turbine performance in terms of aerodynamics, cooling, life time, etc. In addition, these results have given a strong basis for future upgrade, e.g., potential cooling air saving has been identified on several areas. The first SGT-800 with 50.5 MW rating was successfully operated and tested during the spring 2010 and the expected performance figures were confirmed. Up to January 2013, the fleet of this new rating has accumulated >40 000 Equivalent Operation hours (EOH), while the fleet leader has accumulated >16 000 EOH. A planned follow up inspection was made after 10 000 EOH by using borescope for the hot section, and it showed that all the turbine parts were in good condition.

Electrochemical Behaviours of Titanium Nitride (TiN) and Chromium Nitride (CrN) Based PVD Coating Systems

Hard coatings applied to steel components prevent corrosion attacks while at the same time mitigate erosion attack. However, the presence of process related through-coating defects such as pin holes, voids and growth defects, provides accesses for corrosive media to metal substrates, initializing pitting corrosion and eventually resulting in coating failure. This research studies the corrosion behavior of PVD TiN and CrN (CrSiCN) coated steels in 3.5 wt. % NaCl aqueous solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results revealed that in a coating-substrate system, effective diffusion coefficient and diffusion layer thickness control the corrosion resistance; both factors are found to be related to coating microstructure. A denser and thicker coating structure are shown to have lower effective diffusion coefficients and greater effective diffusion layer thicknesses and consequently provided a high resistance to electrochemical corrosion.

Effect of Water Temperature on the Performance of Gas Turbine Inlet Air-Fogging Systems

With more than 1000 fogging systems installed worldwide on a wide range of gas turbines of different types, gas turbine inlet air fogging systems have become a well-established technology used to increase gas turbines power output. The major benefit of spraying fog droplets in the inlet airflow of the gas turbines is to increase the density of the air entering the gas turbine by evaporative cooling in the inlet air stream. Significant amount of research has been carried out to improve the efficiency of fogging systems. However, the effect of water temperature on the overall efficiency of a fogging system has yet to be addressed. In this paper, a detailed analysis of this effect will be presented, both from an experimental and a theoretical view point. Due to the small size of the droplets used in this application, the temperature of the droplet converges quickly to the wet bulb temperature, regardless of the initial water temperature. The rapidity at which this convergence occurs depends on the initial droplet size, the water temperature, the air mass flow to mass of injected water ratio, and the ambient psychrometric conditions of the surrounding air. The present study was carried out using water temperatures between 1 °C and 60 °C. Results showed that the water temperature has no significant effect on the droplet size. However, within the range of droplet sizes atomized from nozzles installed in the fogging system, using cold water provides a marginal benefit on the cooling efficiency; using hot water, on the other hand, slightly increases the evaporation efficiency.

Evaluation of Commercial and Next Generation Alumina-Forming Austenitic Foil for Advanced Recuperators

Alumina-forming austenitic (AFA) steels represent a new class of corrosion- and creep-resistance austenitic steels to enable higher temperature recuperators. Several commercial batches of the first AFA composition have been produced with different thicknesses and widths over 39cm. This commercial AFA foil was successfully folded by two manufacturers. Creep and laboratory oxidation results at 650°-800°C are presented to compare to conventional recuperator alloy performance. While this initial effort was successful, concerns with cost and ease of production suggested that a leaner AFA composition with a lower final annealing temperature would be more attractive for commercial applications. Therefore, several new AFA compositions are being evaluated in laboratory trials and compared to the initial material for down selection of a better AFA composition for commercialization.