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J. Eng. Gas Turbines Power. 2019;141(7):071001-071001-10. doi:10.1115/1.4042131.

The IMO tier III legislation, applicable to vessels with a keel laying date from Jan. 1, 2016, has compelled engine builders to apply new technologies for NOx abatement. One of the most promising technologies for tier III compliance is the selective catalytic reduction (SCR) of nitrogen oxides (NOx). Despite that SCR technology has been applied in powerplants and heavy duty truck engines for years, there are challenges that stem from its applications in large two-stroke marine diesel engines. In this paper, an SCR model applicable to large two-stroke marine diesel engines is introduced. The goal of the model is to predict the thermal response of a marine SCR aftertreatment system when the engine undergoes transient loading. The model has been developed and validated using testbed measured data from a large two-stroke marine diesel engine. The output of the model is the SCR outlet temperature. It is shown that the model can accurately predict the transient inertial response of the SCR during engine acceleration, deceleration, and low load operation.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2019;141(7):071002-071002-10. doi:10.1115/1.4042286.

This work investigated the damage severity of an unmanned aerial vehicle (UAV) ingestion into fan models of a midsized business jet engine. The ingestion of the quadcopter UAV model into the fan was carried out in ls-dyna. The material models used for the quadcopter and the fan were previously validated, and the fan's durability was simulated through simulated bird ingestions. The results of this work show that UAVs will cause significantly more damage than birds due mostly to the hard components typically used in motors, batteries, and cameras. Particular parameters of the ingestion studied include the phase of flight of the plane, impact location and orientation, and fan blade thickness.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2019;141(7):071003-071003-12. doi:10.1115/1.4042167.

The compressor surge is a phenomenon which has to be avoided since it implies the deterioration of performance and leads to mechanical damage to the compressor and system components. As a consequence, compression system models have a crucial role in predicting the phenomena which can occur in the compressor and pipelines during operation. In this paper, a dynamic model, developed in the matlab/simulink environment, is further implemented to allow the study of surge events caused by rapid transients, such as emergency shutdown events (ESD). The aim is to validate the model using the experimental data obtained in a single-stage centrifugal compressor installed in the test facility at Southwest Research Institute. The test facility consists of a closed loop system and is characterized by a recycling circuit, and thus a recycling valve, which is opened in case of surge or driver shutdown. Simulations were carried out at 17,800 and 19,800 rpm; the comparison with experimental data showed the accuracy of the model in simulating different opening rates and different sizes of the recycle valve, at both low and high suction pressure (HSP). Moreover, different actions for recovering/preventing surge were simulated by controlling different valves along the piping system and by adding a check valve immediately downstream the compressor. The results demonstrated the fidelity of the model and its capability of simulating piping systems with different configurations and components, also showing, qualitatively, the different effects of some alternative actions which can be taken after surge onset.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2019;141(7):071004-071004-15. doi:10.1115/1.4042311.

In order to further study the effects of the target channel shape on the cooling performance of the double swirl cooling (DSC), five double swirl channels formed by two overlapping elliptic cylinders with different length ratio between the vertical semi-axis and the horizontal semi-axis are applied. Numerical studies are carried out under three Reynolds numbers. The flow characteristics and heat transfer performance of five DSC cases are compared with the benchmark impingement cooling case. The flow losses, cross-flow development, generated vortices, and velocity distributions inside target channels are illustrated, analyzed, and compared. The spanwise averaged Nusselt number, Nusselt number distributions, and thermal performance are discussed and compared. Results indicate that the largest length ratio between the vertical semi-axis and the horizontal semi-axis of the target channel yields the lowest flow loss, largest overall averaged Nusselt number, and best thermal performance. With the decrease in the length ratio, the heat transfer distribution on the target surface becomes more uniform. The maximum enhancement of overall averaged Nusselt number and thermal performance in DSC is about 30% and 33%, respectively.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2019;141(7):071005-071005-13. doi:10.1115/1.4042010.

This paper describes results from an experimental study on influences of liquid fuel properties on lean blowout (LBO) limits in an aero-type combustor. In particular, this work aimed to elucidate the roles of fuel chemical and physical properties on LBO. Fuel chemical properties stem from the fuel chemical structure, thus governing chemical kinetic behaviors of oxidation characteristics (e.g., ignition or extinction time scales) and others (e.g., fuel thermal stability or sooting tendencies). Fuel physical properties affect the spray characteristics (e.g., atomization and evaporation rates). Eighteen different fuels, with a wide range of physical and chemical fuel properties, were tested. Several of these fuels were custom blends, developed to break intercorrelations between various physical and chemical properties. Fuel physical and chemical property effects were further separated by measuring blowout boundaries at three air inlet temperatures between 300 and 550 K, enabling variation in vaporization rates. The condition at 300 K corresponds to a temperature that is less than the flash point for most of the studied fuels and, therefore, forming a flammable mixture was challenging in this regime. The opposite scenario occurred at 550 K, where fuel droplets evaporate quickly, and the temperature actually exceeds the auto-ignition temperatures of some of the fuels. At 300 K, the data suggest that blowout is controlled by fuel physical properties, as a correlation is found between the blowout boundaries and the fuel vaporization temperature. At 450 and 550 K, the blowout boundaries correlated well with the derived cetane number (DCN), related to the global chemical kinetic reactivity.

Commentary by Dr. Valentin Fuster
J. Eng. Gas Turbines Power. 2019;141(7):071006-071006-9. doi:10.1115/1.4042396.

The present study concerns the leakage predictions in pressure annular centered seals operating in a two-phase (gas–liquid) smooth stratified flow pattern. In such systems, the liquid experiences centrifugal forces typically 3–4 orders of magnitude larger than the standard earth gravity. Consequently, it is reasonable to assume the liquid is centrifuged toward the stator, leaving the rotor in contact only with the gas. This specific flow configuration is difficult to investigate experimentally, being the rotor–stator clearance of the order of 100 μm. For this reason, a new bulk model based on a two-phase smooth-stratified flow is proposed for leakage predictions. The (external) liquid flow and the (internal) gas one are assumed in laminar and turbulent regime, respectively. The results show that for convenient values of the inlet and outlet pressure loss coefficients, the stratified model predicts mass flow rates in better agreement with experimental data than a standard homogeneous multiphase bulk model.

Commentary by Dr. Valentin Fuster

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