Turbocharger Design - ICE Supercharging Units - Heading

Contents

INTRODUCTION

1. Design of pressurizing unit

1.1. Turbocharger design requirements

1.2. Trends of turbocharger development and improvement

2. Construction of engine HSV and selection of design mode of operation

3. Gas dynamic calculation of turbocharger

3.1. Calculation of required pressurization pressure and section of turbine casing

3.2. Gas dynamic calculation of compressor

3.3.Gazodynamic calculation of the turbine

4. Development of joint characteristics of compressor and engine

5. Device of turbocharger and its units

5.1.Compressor stage

5.2.Turbine stage

5.3 Bearing Assembly

5.4.TKR seals

CONCLUSION

List of literature:

Appendix 1. Results of calculation of required pressurization pressure and turbine casing section

Appendix 2. Gas dynamic calculation of compressor with blade-free diffuser

Appendix 3. Gas dynamic calculation of turbine with airless guide vanes

Introduction

As a result of the increase in the share of goods transported by trucks, the requirements for specific capacity indicators of diesel engines increased. The share of diesel engines among cars, including cars, is also growing. In recent years, due to the gradual deterioration of the environment, more and more attention has been paid to reducing harmful emissions from internal combustion engines.

The introduction of gas turbine pressurization has a positive effect on improving the specific capacity, economic and environmental performance of the engine. For pressurization, usually vane compressor machines are currently used, due to their compactness and relatively simple design. The supercharged engine has a number of drawbacks, such as the worst acceptance, the difficulty in providing the excess air coefficient necessary for environmental indicators in the low engine speed zone.

During the course project the following tasks are solved:

1. Gas dynamic calculation of compressor and turbine stages.

2. Selection of type of turbocharger and justification of its structural scheme, arrangement of turbocharger elements.

3. Construction of the joint characteristic of the engine and compressor.

4. Analysis of engine and compressor joint operation for the specified engine operation mode.

1. Design of pressurizing unit

1.1. Turbocharger design requirements.

Due to the variety of conditions under which the turbocharger of an automobile engine must operate, it must meet the following requirements:

• turbocharger shall provide the required quantity

air for fuel combustion at all engine operation modes, including acceleration ones, to fulfill the specified standards for economy and ecology. At the same time, its efficiency should be maximum possible, but not less than 50%, and the moment of inertia of the rotor should be minimum;

• the turbocharger shall operate reliably in any conditions of operation of the transport engine, and its service life shall not be less than the service life of the engine itself;

• turbocharger must have a certain margin for rotor speed in order to maintain operability in extreme engine operating conditions, such as "spacing," operation in high mountain conditions. Bearings shall ensure reliable operation of TCR up to the limit speed of rotation;

• turbocharger, its parts and assemblies shall function normally under conditions of pulsating flow and cyclically changing gas temperature characteristic of piston engines and creating mechanical and thermal loads of variable nature;

• turbocompressor must withstand multiple engine starts when oil supply to bearings is delayed, as well as abrupt stops after high-speed and load engine operation modes;

• The turbocharger shall be operated on the same oil as the engine without requiring additional cleaning. The turbocompressor shall have reliable seals to prevent oil ingress into the compressor and turbine ducts as well as air and gas into the engine crankcase;

• During the entire service life, the turbocharger should not require maintenance, its design should ensure easy installation of the turbocharger on engines of various layout schemes, have good weight and size;

• The cost of the pressurizing system shall not exceed the cost of increasing the engine power by increasing its working volume;

• The turbocharger shall be operable and shall be repaired at minimal cost and shall not require complex machine tools.

Such complex, diverse and contradictory requirements are met by the TCR layout scheme with a centrifugal wheel and a centripetal turbine cantilever located on both sides of the bearings.

5.1.Compressor stage.

Compressor stage of turbocompressor includes impeller, diffuser, housing (air collector) with inlet device and outlet branch pipe.

In compressor stages, mainly two-tier

wheels (blades at the wheel inlet are shortened through one) with rearward bent blades, which provide higher efficiency compared to wheels having radial blades. The use of rearward bent blades became possible after the development and mastery of the technology of casting wheels according to plastic models into gypsum molds. In addition to the fundamental possibility of manufacturing wheels with curved blades, this technology allows significantly improving the cleanliness of the surface of the blade channels. The channels in the wheel are specially shaped in order to ensure an irreversible flow with minimal losses. In order to ensure sufficient vibration resistance, the wheel blades have a variable radius thickness estimated by the widening angle γ. The value of efficiency is influenced by the gap between the contours of the wheel and the housing, which for the made structures is 0.50.6 mm. The compressor wheel is put on the shaft by transition fit, so when the rotor is assembled and disassembled, it is usually heated to 150200 ° C. In order to ensure sufficient vibration resistance, the wheel blades have a variable radius thickness estimated by the widening angle .

The inlet portion of the housing is generally in the form of a confuser. It

allows a smooth transition from the engine intake line, where, as a rule, the air speed is not more than 30 m/s. Of the remaining elements, note the dimensions of the compressor wheel sleeve, which should ensure metal removal during balancing. Its relative size is within (0.20.25) and its length is within (0.040.08) of the outer diameter of the wheel.

For conversion of kinetic energy of flow after wheel to

static pressure uses a diffuser and a snail-type housing. Automotive ICE compressors use mainly blade-free diffusers. The width of the slit of the blade-free diffuser is typically 1.52 times the width of the wheel at the outlet to provide some "compression" of the flow and alignment of the speed range. Outer diameter of blade-free diffuser makes 1.31.6 of wheel diameter. The rear wall of the diffuser in some structures is made in a cover detachable from the bearing housing. There may be no sealing elements between the housing and the cover. Body outlet branch pipe is made expanding and connected with engine inlet manifolds or supercharging air cooler.

The maximum adiabatic efficiency of compressor stages of modern designs reaches values ​ ​ of 0.82 and has a certain tendency to decrease with a decrease in wheel diameter. For example, for the HOLSET NVV TCR with a wheel diameter of 108 mm, the maximum efficiency is 0.825, and for the MITSUBISHI TD04 TCR with a diameter of 49 mm - 0.73.

5.2.Turbine stage.

The turbine stage by the nature of the work can be of two types: impulse and isobaric. The pulse turbine operates in a pulse gas stream when the gas parameters change over time and the isobar turbine operates in a gas stream with constant gas parameters. For supercharging of piston ICE, in which almost all processes are cyclic, mainly pulse turbines are used.

Turbine stage includes impeller and turbine housing with guide vanes. In modern TCR of the autotractor type, in most cases, blade-free guide vanes are used in combination with an open or semi-open type turbine wheel. The open-type turbine wheel has practically no disk, the semi-open wheel has a ratio of the diameter of the disk to the diameter of the turbine wheel in the range of 0.490.78. In order to reduce the moment of inertia, the wheels try to make the diameter of the hub as small as possible. The turbine wheel with radial blades is made by casting using smelted models from heat-resistant nickel alloy of INKO713S, ANV-300 type and the like. It is connected to the shaft by friction welding. Blades of turbine wheel to provide strength have own frequency of oscillations not less than 8-9 kHz, which is achieved by making blade with variable thickness along radius. Recently, many foreign companies have been engaged in intensive development of ceramic turbine wheels and some of them are already ready to start their mass production.

The casings of isobar turbines are used as an exception and can have a different shape of the section of the snail: round, trapezoidal, pear-shaped, Pulse turbines are made with casings having two adjacent snails separated by a partition. The channel of the turbine housing with the inlet guide vanes is specially shaped to provide the necessary gas speeds at the inlet to the wheel.

The body is made of heat resistant cast iron. Clearance between wheel and turbine casing strokes does not exceed 1 mm. The turbine housing is fixed to the bearing housing in most cases with bolts, various "non-stick" pastes are used. The terminal connection remained only with isobaric turbines, in which the housing can be made relatively narrow.

Achieved efficiency of modern turbines

turbocompressors are: 0.60.7 depending on wheel diameter.

5.3.The bearing assembly.

Turbocompressor bearing assembly consists of rotor, bearing housing with bearing bushings installed in it. Rotor represents shaft welded with turbine wheel and compressor wheel fitted thereon and parts of thrust bearing and seals. The parts of the rotor are tightened by a nut with a torque of about 40 N m (4 kgm), which can be stopped from being unscrewed by sealant or other methods.

In turbocompressors of the autotractor type, "flexible" rotors are used, in which both critical speeds are within the operating speed range. Diameter of rotor shaft makes 0.150.25 from outer diameter of compressor wheel, distance between middle of bearings is three five diameters of shaft. Very high requirements are placed on the accuracy and cleanliness of the working surfaces of the bearings and the rotor shaft. Ellipsicity, cutting, taper and other deviations from round and rectilinear shape are practically not allowed on the rotor necks. Roughness of rotor working surfaces must be not more than Ra 0.4. The rotor is dynamically balanced separately: the turbine wheel with the shaft and the compressor wheel, each in two planes perpendicular to the axis of rotation. The accuracy of dynamic balancing is (0.10.15) 104N m (0, l0.1 5 gsm).

Axial movement of the rotor is limited by thrust bearing, which perceives axial forces arising during TCR operation on the engine. The axial play of the rotor is about 0.1 mm.

Modern TKR uses sliding bearings of the "floating" type, which differ from ordinary sliding bearings by the presence of a second oil layer between the bushing and the housing. This outer oil layer is designed to dampen vibrations that occur when the rotor rotates at a high frequency. The bearing sleeve rotates at a high speed, reaching 1/3 of the shaft speed in some structures. However, the rotation of the sleeve has a negative side. when insufficiently purified oil enters bearings under the action of centrifugal effect, particles of contamination enter mainly into the outer gap, intensifying wear of conjugated surfaces of bushing and bearing housing. However, the vast majority of foreign companies use floating rotating bushings (BP) as bearings.

Ratio of outer diameter of rotating bushing to inner diameter is within 1.51.65. Lubrication is supplied to bushings and thrust bearing via drilled channels, fine oil cleaning for such bearings is set to not more than 20 mcm. Turbocompressors are produced, in which the bushings are combined into a single shaft, which, while maintaining a "floating" effect, is kept from rotation by a stop pin or a spring bracket. Such a structure is designed to reduce wear of mating surfaces forming an outer gap. Clearance between shaft and bushing is 0.040.06, between bushing and housing - 0.090.15 mm.

Such a bearing assembly has been folded for many years and with proper reliability of the lubrication system and high-quality filtration provides sufficient durability for at least 10 thousand hours. The main parameter, which constantly and gradually increases, is the thickness of the floating sleeve or the ratio of the outer diameter of the sleeve to the diameter of the shaft. Currently, this value has stabilized at 1.6 in almost all TCR models. This led to a significant decrease in the speed of rotation of the sleeve, and in some modes and to its complete stop.

5.4.TKR seals.

The variety of seal assembly designs, especially on the compressor side, indicates a continuous search for a seal that satisfies the operating conditions of the TCR on the transport engine. Seals of modern TCR are a combination of oil reflectors, protective shields and sealing rings. It is especially important to avoid oil penetration into the compressor cavity, as this is facilitated by the presence of a vacuum in front of the compressor, which can reach values ​ ​ of 700 mm of water. Art., and sometimes more. The efficiency of the seal depends on many factors: the diameter of the O-rings, the quality of the manufacturing of the parts, the volume of the drain cavities, the flow of oil through the bearings, the design of the screen and other elements. Examples of domestic and foreign designs show the possibility of preventing oil leaks even at very high

vacuum upstream the compressor.

Leaks through the turbine seal occur only with very worn out parts, since it is constantly, even at engine idle speed, under the pressure pressure of the exhaust gases. A large amount of gas can pass through the leaking seals into the crankcase cavity of the engine, increasing the pressure in it above the permissible limits.

Conclusion

In the course of this course work, the compressor and turbine stages of the turbocharger were calculated, the main sizes of these stages were determined, graphs of changes in full, static parameters and absolute gas flow rate along the sections of the turbocharger were built.

A turbocharger was also designed in the project, its design features were described, and it was compared with existing turbocharger designs. A joint characteristic of the engine and compressor was built, the possibility of joint operation of the turbocharger and engine was analyzed. Modern trends of turbochargers development are considered