Manipulating Frictional Performance of Wet Clutch Engagement through Material Properties and Operating Conditions

Wet clutch engagement is mainly influenced by the frictional behaviors between the friction pad and steel plate as well as the lubrication behaviors. A positive μ–V friction coefficient of the wet clutch pad is the most preferable characteristic for improving antishudder behavior. In this study, a wet clutch engagement mechanism is theoretically divided into two major frictional behaviors, namely, direct asperity contact of interacting surfaces and hydrodynamic lubrication, for positive μ–V friction performance. These two behaviors are investigated with regard to both material characteristics of the friction pad–steel plate interactions and hydrodynamic lubrication mechanism. Frictional interactions of the friction pad are analyzed according to the material properties of the friction pad, such as elasticity, permeability, and roughness. Hydrodynamic lubrication, by which the initial period of the engagement is dominantly governed by the waviness of surface shape, is investigated to increase the frictional resistance in the initial stage of engagement relative to that in the final stage of engagement for realizing a positive μ–V friction coefficient. Computational simulations of wet clutch engagement behaviors are performed and compared with each other to obtain positive μ–V friction characteristics of the friction pad

Internal Damper Characteristics of Rotor System with Submerged ER Fluid Journal Bearing

Electro-Rheological (ER) fluid behavior is similar to Bingham fluid’s. Only when the shear stress magnitude of ER fluid exceeds the yield stress, Newtonian flow results. Continuous shear strain rate equation about shear stress which simulates Bingham-like fluid shows viscosity variations. Shear yield stress is controlled by electric fields. Electric fields in circumferential direction around the journal are also changeable because of gap distance. These values make changes of spring and damping coefficients of journal bearings compared to Newtonian flow case. Implicit viscosity variation effects according to shear strain rates of fluid are included in generalized Reynolds' equation for submerged journal bearing. Fluid film pressure and perturbation pressures are solved using switch function of Elord's algorithm for cavitation boundary condition. Spring and damping coefficients are obtained for several parameters that determine the characteristics of ER fluids under a certain electric field. From these values stability region for simple rotor-bearing system is computed. It is found that there are no big differences in load capacities with the selected electric field parameters at low eccentric region and higher electric field can support more load with stability at low eccentric region

Nitric Oxide Emission Reduction in Reheating Furnaces through Burner and Furnace Air-Staged Combustions

In this study, a series of experiments were conducted on a testing facility and a real-scale furnace, for analyzing the nitric oxide (NO) emission reduction. The effects of the temperature, oxygen concentration, and amount of secondary combustion air were investigated in a single-burner combustion system. Additionally, the NO-reduction rate before and after combustion modifications in both the burner and furnace air-staged combustion were evaluated for a real-scale reheating furnace. The air-to-fuel equivalence ratio (λ) of individual combustion zones for the furnace was optimized for NO reduction without any incomplete combustion. The results indicated that the NO emission for controlling the λ of a single-zone decreased linearly with a decrease in the λ values in the individual firing tests (top-heat, bottom-heat, and bottom-soak zones). Moreover, the multi-zone control of the λ values for individual combustion zones was optimized at 1.13 (top-preheat), 1.0 (bottom-preheat), 1.0 (top-heat), 0.97 (bottom-heat), 1.0 (top-soak), and 0.97 (bottom-soak). In this firing condition, the modifications reduced the NO emissions by approximately 23%, as indicated by a comparison of the data obtained before and after the modifications. Thus, the combined application of burner and furnace air-staged combustions facilitated NO-emission reduction