Locomotive Turbocharger Research Articles

Design of herringbone grooved thrust bearing for locomotive turbocharger rotor

The herringbone texture exhibited excellent tribological performance to minimize friction and wear. However, the application of this texture in the development of grooved thrust bearings is limited. Therefore, in this study, an attempt was made to design an oil-lubricated herringbone grooved thrust bearing for high-speed locomotive turbochargers. The designed bearing accommodates the axial load generated due to the pressure difference between the turbine and compressor wheel. The bearing design starts with applying Newton’s second law to predict the thrust load acting on the locomotive turbocharger rotor. The thrust load is calculated analytically and is found to be 4.54 kN for a design rotor speed of 1,00,000 rpm. Further, the herringbone grooved thrust bearing has been modeled numerically using non-linear Reynolds equation. The modified Reynolds equation is discretized using the finite volume method (FVM) and solved by successive over-relaxation (SOR) methodology to determine the static characteristics over the bearing surface. The developed HGTB is found to have a suitable load-carrying capacity of 4.6 kN, frictional torque of 0.25 N.m, and power loss of 2.98 kW. Further, a parametric analysis has been carried out to study the influence of design parameters such as the number of grooves, helix angle, angular groove width, groove depth, and speed on load-carrying capacity, frictional torque, and power loss.

A method for modeling and analyzing the rotor dynamics of a locomotive turbocharger

The rotor of the locomotive turbocharger is prone to malfunction of the turbocharger, and it is also the most important part of the turbocharger. The reasonable establishment of rotor dynamics model is very important in the study. It determines the accuracy of analysis. The influence of the shaft quality on the turbine and impeller was not considered in the process of analyzing the dynamic model in the passed research. But the quality of locomotive turbocharger rotor shaft is relatively large, it cannot be ignored because it will have a large bending moment in the model simplified. So the rotor dynamic equation was deduced in the case of considered the quality of the rotor axis. The rotor of the turbocharger rotor was simplified firstly, the various parts of the simplified rotor were analyzed, and the dynamic model of the rotor was established. And the dynamic model was verified by the hammer experiment. The factors considered in the dynamic model were more comprehensive, so the model would be more practical for the future research.

Failure Analysis of the Related Components of a Locomotive Turbocharger

A locomotive turbocharger assembly suffered from destruction during a trial operating for 120 h. The damaged components include worm-housing, impeller blades and impeller-cover, main-shaft, bearing-sleeve, and main-shaft bolts. Fracture, deformation, and wear to varying degrees occurred on the components. The damage and fractography features on the failed components were investigated to identify the troublemaker in this incident and the root cause of turbocharger destruction. The investigation indicates that thread stripping on the wall of bolt holes on the flange at the inlet end of worm-housing induced the destruction of the whole turbocharger assembly. The specified material of worm-housing is gray cast iron (HT 250) and the specified low limit of tensile strength is 250 MPa. Unexpectedly, the tensile strength of the failed worm-housing material is about 70% of the specified low limit. The low strength of worm-housing material is mainly responsible for thread stripping of the bolt holes on the flange. The carbon content of worm-housing material exceeds the specified upper limit. Excessive graphite and long and thick graphite flakes in the worm-housing material resulting from high carbon content or maybe from unsuitable foundry practices led to low hardness and low strength of worm-housing material.

Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve

A failure investigation was conducted on a locomotive turbocharger main shaft and a bearing sleeve which had been assembled with the main shaft. The fracture of the main shaft took place at a sharp edged groove between two journals with different cross-sectional areas. The dominant failure mechanism of the main shaft was low-cycle and rotation-bending fatigue. Wear failure occurred on the bearing sleeve through a mixed mode of abrasive and adhesive wear. Detailed metallurgical analysis indicated that the bearing sleeve and the journal surface assembled with the sleeve had been subjected to abnormally high temperatures which led to increased friction between the bearing sleeve and the bearing bush, the sleeve, and the journal surface. In addition, the abnormally high temperature softened the induction-hardening case on the journal surface and decreased the fatigue strength. Fatigue crack initiation occurred at the root fillet of the groove because of the stress concentration in that area.

Failure Investigation on Inducer Blades of Locomotive Turbocharger

Damage to varying degrees including fracture, cracking, and scraping occurred on inducer blades used in a locomotive turbocharger which had run for 3626 km. The blade fracture was formed by the propagation of axial and radial cracks forming an L-shape. Fractography investigation indicates that the axial fracture mode of the blade was by fatigue. The radial fracture was formed by one instantaneous crack. A strike dent was present on the leading edge of the fractured blade and this dent became the initiation site of fatigue crack. Failure of other blades was subsequent to the original fracture.

Damage Features of Bolts Connecting Main-Shaft with Turbo-Disk Used in a Locomotive Turbocharger

The connection between the turbo-disk and the main-shaft was found to be loose when performing a regular inspection on a locomotive turbocharger. When the bolts connecting main-shaft with the turbo-disk were disassembled, it was found that smeared threads and contact pressing deformation, etc., severe plastic deformation took place on the three connecting bolts. Metallurgical examinations indicate that the core microstructure is composed of the banded ferrite and pearlite along the axial other than the sorbite by the standard toughening process (quenching and tempering). Abnormal microstructure leads to low the hardness and strength so that various damages appeared on the flanks when twisting bolts with nuts (loosening or tightening). The plastic deformation took place on the bolts under the axial load due to low hardness, which resulted in loosening of the connection between the turbo-disk and the main-shaft. Not standardized fabrication process of the bolts is responsible for the failure of the bolts.

Failure analysis on connection components of turbo-disk and main-shaft used in a locomotive turbocharger

Three bolts, three pins connecting turbo-disk and main-shaft and the navel of turbo-disk fractured during servicing, which were used in a locomotive turbocharger. Examination and analysis results show that one of location pins was not riveted into the pin hole on the plate of the main-shaft due to dislocation. The pin encountered greater hammering force and resistance to moving downward when being riveted into the hole, so corresponding impact tensile load was exerted on opposite bolt and the navel. The cracks initiated at the last engaged thread root of the bolt and the root fillet of navel and propagated in fatigue mode under the action of alternative loads. The bolt and the navel fractured first. Other components fractured in succession. Defective operation of riveting is responsible for the fracture of connection components.

Failure analysis of a locomotive turbocharger main-shaft

A failure investigation has been conducted on a locomotive turbocharger main-shaft. The fracture position is located at a sharp edged groove between two journals with different cross-sectional area. Fractography investigation indicates that the rotating bending fatigue is the dominant failure mechanism of the main-shaft. Detailed metallurgical analysis indicates the root fillet region of the groove had subjected to abnormal high-temperature resulting from the intense friction between the bearing-sleeve and the assisted pushing bearing, which makes the fatigue strength of the root fillet region of the groove decrease. Over-small root fillet radius of the groove by which stress concentration is created facilitates the fatigue cracks to initiate in the root fillet region.

Failure investigation on failed inducer blades used in locomotive turbocharger

Inducer blades used in a locomotive turbocharger were found damaged to varying extents servicing for 1000 km. The damages were in the form of fracture, crack and scrape. The fractures show L-shape, which were formed by propagation of axial crack and radial crack. Fractography investigation indicates the multiple origins fatigue is the main failure mechanism of the fractured and cracked blades. Fatigue crack origins are at the blade root with the coarse axial machining marks. The blade root thickness is over-small, which makes the average stress lever at blade root increase. Presence of the coarse axial machining marks at the blade root and over-small thickness of the blade root are responsible for the fatigue failure of the blades. Blades opposite the fractured blades were touched by the worm-shell outside the inducer due to swinging eccentrically of the inducer and the friction between them was operated so that the serious circumferential scrape took place at the edges of the blade-tips.

Failure Investigation on Failed Blades Used in a Locomotive Turbocharger

A failure investigation has been conducted on the turboblades used in a locomotive turbocharger. These blades are made from as-cast K418 nickel-base (Ni-base) superalloy. Fracture occurred at the mid-airfoil and tip locations. In the mid-airfoil regions, a high density of intergranular cracks and dent marks are present. The microstructure at the mid-airfoil is typical of overheat damage, such as melting of the boundary or interdendritic region and degraded interdendritic carbides and remelting of eutectic phases (γ + γ′). The fracture surfaces of the failed blades have a dendritic appearance without evidence of fatigue features. It is suggested that these fractures were formed instantaneously. Overheat damage made the strength in interdendritic region decrease so that microcracking occurred preferentially in the interdendritic region. Under the action of bending stress and the spin centrifugal tensile stress, the microcracks propagated within the interdendritic region and converged so that the transverse fracture occurred at the mid-airfoil location where the maximum stress acted. The fragments from previously fractured blades hit neighboring blades, ultimately causing damage to all the turboblades.