Increased durability of the piston group of the UTD-20 diesel engine - heading

Contents

Introduction

1. Analysis of the existing design of the diesel piston group UTD-

1.1 Purpose and operating conditions of piston group of UTD- diesel engine

1.2 Working Conditions

1.3 Requirements................................................................................................. 5-

1.4 Arrangement of the piston group of the UTD-20 diesel engine, materials and technologies used..................................................................................................................................................................................................... 6-

1.5 Basic design parameters

1.6 Assessment of a design of piston group of the UTD-engine

2. Calculation of oil cooling nozzles............................................................................................................................. 9-

3. Evaluation of the designed design

Conclusion

List of literature

INTRODUCTION

The growth of forcing of modern diesel engines is largely limited by the operability of the piston group, and above all by the acceptable level of temperatures and stresses in the engine piston.

Undoubtedly, the piston is the most loaded part of the engine. Combined mechanical and thermal loads are applied to the piston during engine operation. It is impossible to separate them, since any material changes its properties with an increase in temperature. A piston that easily withstands existing loads at engine operating temperature will be destroyed under the influence of unchanged mechanical loads in case of engine overheating.

Mechanical loads on the piston

During the operation of the engine, significant mechanical loads are exerted on the piston, constantly changing both in direction and in magnitude. Even while the vehicle is moving quietly, evenly on a normal road, the engine crankshaft rotates at approximately 1500 rpm, hence within one minute the piston must accelerate to a high speed, stop and again accelerate in the opposite direction 2,000 times per minute, or 50 times per second. If we assume that the average piston stroke of a modern short-stroke engine is 80 mm, in one minute the piston will pass 480 meters, that is, the average piston speed in the cylinder is 28.8 km/h.

One can imagine what large inertial loads affect the piston, even if one simply assumes that the crankshaft of the engine rotates from an external energy source. But the piston is also affected by the compressible gas force on the compression stroke and by the particularly beneficial action of the expandable gases on the stroke stroke. The maximum pressure in the combustion chamber of a high-speed engine reaches 80-100 atmospheres, the pressure in the combustion chamber of a conventional car 55-60 atmospheres. And if we assume that the diameter of the piston of the middle car is 92 mm, at the moment of maximum pressure, the piston experiences a force of 5.3 to 6.6 tons. So it can be said that the piston of the car, like other parts of the crank mechanism, experiences huge mechanical loads. But the trouble does not come alone, except for significant mechanical loads, the piston is also exposed to very high temperatures.

Thermal loads on the piston

Where does the heat that affects the piston come from? The first, but not the main, source of this friction. During engine operation, the piston moves at high speed, while it constantly rushes against the cylinder walls. The geometry of the crank mechanism is such that part of the force applied to the piston is used to press the piston against the cylinder walls. And despite the high-quality treatment of surfaces, both the cylinder and the piston, even if there is a lubricant, a sufficiently large friction force occurs.

Where does the heat that affects the piston come from? The first, but not the main, source of this friction. During engine operation, the piston moves at high speed, while it constantly rushes against the cylinder walls. The geometry of the crank mechanism is such that part of the force applied to the piston is used to press the piston against the cylinder walls. And despite the high-quality treatment of surfaces, both the cylinder and the piston, even if there is a lubricant, a sufficiently large friction force occurs.

But basically, the heat acting on the piston appears when the fuel-air mixture burns in the engine cylinder. The temperature of gases burned in the cylinder can reach 2000-2500C. Under the influence of such high temperatures, all structural materials from which the parts of modern internal combustion engines are made are destroyed. Therefore, it is necessary to remove heat from the most heat-loaded parts of the engine and, of course, from the pistons.

Increasing the average effective pressure by only 0.1 MPa leads to an increase in piston temperature by 11140 С, ring temperature by 360 С, and with an increase in diesel crankshaft speed by 100 min-1, the piston temperature increases by 360 С. Under these conditions, the use of oil cooling of pistons is the most effective way to increase the operability of the cylinder-piston diesel group. Based on this problem, in my course design, I decided to improve the design of the piston group of the UTD20 diesel engine used on BMP2 by using jet cooling on the internal surface of the piston on this engine.

The total amount of heat generated during operation of the engine depends on the amount of fuel burned in the cylinders of the engine per unit time. And this indicator, in turn, depends on the volume of the cylinders and on the speed of rotation of the engine. The engine turns into useful mechanical work only a small part of the energy of the burned fuel. Some heat is removed from the engine with hot exhaust gases and the rest of the heat must be dissipated in the surrounding space.

If the two bodies have different temperatures, but the heat from the more heated body moves to the less heated body until the temperature of both bodies is equal.

In an automobile, the coldest body capable of absorbing a large amount of heat is ambient air, therefore, it is necessary to find a method for removing heat from heated engine parts to ambient air. Since the entire globe still cannot warm, it can be considered that the environment is able to absorb any amount of heat.

The hottest part of the piston is its bottom, since it directly contacts the hot working gases. Then heat spreads from piston bottom towards skirt.

Heat is removed from the piston in three ways:

The main part of the heat is transferred by the piston rings and the piston skirt to the cylinder walls and then withdrawn by the engine cooling system.

Part of heat is removed by internal cavity of piston and through piston pin and connecting rod, as well as by oil circulating in engine lubrication system.

Part of heat is removed from piston by cold fuel-air mixture supplied to engine cylinders.

I had to:

- analyze the existing design of the piston group of the UTD-20 diesel engine

- calculate and design special fixed oil cooling nozzles

- evaluate the developed design of the piston group.

1. Analysis of the existing design of the piston group of the UTD-20 diesel engine

1.1 Purpose and operating conditions of the piston group of the UTD-20 diesel engine

The connecting rod-piston group together with the crankshaft are the main working mechanism of the piston internal combustion engine. The purpose of the piston group is to:

1) perceive gas pressures and transfer these pressures to the engine crankshaft through the connecting rod;

2) seal the above-piston cavity of the cylinder both from gas break into the crankcase and from excessive penetration of lubricating oil into it.

1.2 Working Conditions

The piston group operates under difficult temperature conditions with cyclic abrupt loads with limited lubrication and insufficient heat removal due to cooling difficulties. During engine operation the following forces apply to parts of piston group:

- gas pressure forces

- translational inertia force

- inertia force of rotating masses

- total forces and moments

- force resulting in torque.

1.3 Requirements

Since the piston group is one of the most important operating mechanisms of the piston internal combustion engine, the following requirements apply to it:

- high thermal conductivity and wear resistance of parts

- piston design shall ensure its free movement in the cylinder

- sufficient tightness to prevent gas break from combustion chamber into crankcase and oil ingress from crankcase side into cylinder working space

- corrosion resistance of working surfaces

- high wear resistance

- high strength and rigidity of piston group parts

- processability and low cost

- minimum weight and dimensions.

1.4 Device of the piston group of the UTD20 diesel engine, materials and technologies used:

• piston

• piston pin

• piston rings

• blankings

Piston

The piston is stamped and made of aluminium alloy.

Piston pin

Piston pin of floating type, steel, cemented on external surface, hollow inside.

Piston rings

5 rings.

2 rings sealing, steel, trapezoidal cross-section along the generatrix are covered with porous chromium.

2 combined rings, along with gas burst seal, serve to remove excess oil from the cylinder liner mirror, are made of special cast iron, and are covered with a thin layer of solid chromium.

1, an oil discharge ring made of special cast iron is subject to tinning.

Caps

Made of bronze.

1.5 Basic design parameters

Piston

The calculation of the piston is reduced to the definition:

- dimensions of piston bottom and walls by bending stresses

- piston guide part

- thickness of the first ring jumper

- piston side surface profile

- piston swinging forces

Piston pin

The calculation of the piston pin is based on the determination of bending, cutting and ovalization stresses of the finger.

Piston rings

As a rule, only compression rings are calculated. Calculation is performed for bending of piston ring (Ϭ).

1.6 Design assessment of engine piston group UTD-20

In addition to the heat that the piston receives from the gases, part of the friction heat of the piston group passes into it, and the friction of the piston group is from 45 to 65% of the total friction of the diesel engine, its operation is accompanied by an intensive supply of heat to the piston and unfavorable conditions for removing heat from the piston to the cylinder walls, since the piston is separated from the walls by layers of grease and coke. When the temperature of the piston increases, the mechanical strength of its material decreases, and thermal stresses caused by uneven heating of individual zones of the piston are added to the mechanical loads arising from the pressures of gases and inertia forces.

After analyzing the existing design of the piston group of the UTD20 diesel engine, I came to the conclusion that the cooling of the pistons on this engine is carried out only by spraying oil. Therefore, to increase the heat outflow from the diesel pistons, I decided to introduce special oil nozzles into the engine design, which will provide additional cooling of the internal surface of the piston by oil spraying. Taking into account the correct arrangement of these nozzles, 7580% of the total volume of injected oil will fall into the internal cavity of the piston and as a result - a decrease in the temperature of the piston bottom - 30-350 С, a decrease in the temperature of the zone of the first ring 20250 С.

Conclusion

Installing oil nozzles in the engine for additional cooling of the pistons is far from the only way to increase the service life of the engines. There are still a large number of different upgrades. The result of these upgrades leads to a significant improvement in the consumer and operational qualities of diesel engines, a number of design weaknesses will be eliminated, which lead to a frequent failure of diesel engines.

Ведомость курсового проекта _ ОАБИИ 04. 14 КП 06 ПЗ.cdw

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