Zafer Dursunkaya

An integrated model of ring pack performance

This paper describes an integrated model developed for the detailed characterization and simulation of piston ring pack behavior in internal combustion engines and the prediction of ring pack performance. The model includes comprehensive and coupled treatments of (1) ring-liner hydrodynamic and boundary lubrication and friction; (2) ring axial, radial, and (toroidal) twist dynamics; (3) inter-ring gas dynamics and blowby. The physics of each of these highly inter-related phenomena are represented by submodels, which are intimately coupled to form a design-oriented predictive tool aimed at the calculation of ring film thicknesses, ring motions, land pressures, engine friction, and blowby. The paper also describes the results of a series of analytical studies investigating effects of engine speed and load and ring pack design parameters, on ring motions, film thicknesses, and inter-ring pressures, as well as ring friction and blowby.

A Moving Boundary Problem in a Finite Domain

The heat conduction and the moving solid-liquid interface in a finite region is studied numerically. A Fourier series expansion is used in both phases for spatial temperature distribution, and the differential equations are converted to an infinite number of ordinary differential equations in time. These equations are solved iteratively for the interface location as well as for the temperature distribution

Solidification of a Finite Medium Subject to a Periodic Variation of Boundary Temperature

The motion of a solid-liquid interface in a finite one-dimensional medium, subject to a fluctuating boundary temperature, is analyzed. The fluctuations are assumed to be periodic. The solution method involves a semi-analytic approach in which, at any given time, the spatial temperature distributions are represented in infinite series. The effect of the solid, liquid Stefan numbers and the unsteady boundary temperature variation is investigated. The results showed a retrograde motion of the solidification front for large liquid Stefan numbers.

Experimental Thermal Performance Characterization of Flat Grooved Heat Pipes

ABSTRACT The thermal characterization of aluminum flat grooved heat pipes is performed experimentally for different groove dimensions. Three heat pipes with groove widths of 0.2 mm, 0.4 mm, and 1.5 mm are used in the experiments. The effect of the amount of the working fluid is extensively studied for each groove width. The results reveal that, although all three succeed in dissipating the heat input through the phase change of the working fluid by continuous evaporation and condensation, the effectiveness of the heat transfer increases with reduced groove width. Furthermore, it is observed that there exists an optimum operating point, where the temperature difference between the heating and cooling sections is at a minimum, and the magnitude of this temperature difference is a strong function of the groove width. To the best of the authors’ knowledge, the combined effects of groove dimensions and the amount of the working fluid, from fully flooded to dry, is reported for the first time for aluminum flat grooved heat pipes.

Experimental Investigation of Oil Accumulation in Second Land of Internal Combustion Engines

Blowback of engine oil suspended in combustion gases, when the gas flows from the piston second land back into the combustion chamber, is believed to contribute to oil consumption and hydrocarbon emissions in internal combustion engines. Oil accumulation in the region between top and second compression rings is a factor that influences this phenomenon. The effects of individual parameters, such as oil film thickness and viscosity, however, have still not been understood. The present study was aimed at constructing an experimental setup to study the effect of oil film thickness on oil accumulation in the second land of internal combustion engines. Due to the inherent difficulties of experimentation on production engines, a modeled piston-cylinder assembly was constructed. Total oil accumulation in the modeled second land after a single piston stroke was measured and compared to oil consumption in operating engines.

Three-dimensional grain design optimization of solid rocket motors

This study investigates the ballistic design optimization of three-dimensional grains of solid rocket motors (SRMs). The geometric modeling and burnback analysis of grains are performed analytically by using basic geometries like cylinder, cone, prism, sphere, ellipsoid, and torus. For the internal ballistic analysis, a quasi-steady zero-dimensional flow solver is used. Three different optimization methods are considered: real-coded genetic algorithm (GA), binary genetic algorithm and complex method. The optimization methods are applied to the problems of finding the parameters of grain geometry satisfying an objective thrust versus time profile and maximizing the parameter of total impulse satisfying the constraints of chamber pressure and propellant mass.

An Interferometric Technique for Measuring Micron Level Clearances Filled With a Lubricant

The aim of this study is to develop an interferometric technique to measure micron level clearances occurring in small piston-cylinder arrangements; such as hermetically sealed compressors. A Cartesian model of the piston cylinder arrangement is manufactured and lateral and vertical motions are generated via a step motor, and micrometers, respectively, to simulate the piston motion and the change of clearance during the motion. Experiments are conducted in air and a lubricant. Measurements show the important effect of surface waviness of the mirror and the effect of the motion of the carriage at micron level measurements.Copyright

Development of an Interferometric Technique to be Used in Measuring Micron Level Clearances Filled With a Lubricant

The aim of this study is to develop an interferometric technique to measure micron level clearances occurring in small piston-cylinder arrangements; such as hermetically sealed compressors. A Cartesian model of the piston cylinder arrangement is manufactured and lateral and vertical motions are generated via a step motor, and micrometers, respectively, to simulate the piston motion and the change of clearance during the motion. Experiments are conducted in air and a lubricant. Measurements show the important effect of surface waviness of the mirror and the effect of the motion of the carriage at micron level measurements.Copyright