Lubrication System Diesel Engines

An internal combustion engine would not run for even a few minutes if the moving parts were allowed to make metal-to-metal contact. The heat generated due to the tremendous amounts of friction would melt the metals, leading to the destruction of the engine. To prevent this, all moving parts ride on a thin film of oil that is pumped between all the moving parts of the engine.

Once between the moving parts, the oil serves two purposes. One purpose is to lubricate the bearing surfaces. The other purpose is to cool the bearings by absorbing the friction generated heat. The flow of oil to the moving parts is accomplished by the engine's internal lubricating system.

Oil is accumulated and stored in the engine's oil pan where one or more oil pumps take a suction and pump the oil through one or more oil filters as shown in Figure 12. The filters clean the oil and remove any metal that the oil has picked up due to wear. The cleaned oil then flows up into the engine's oil galleries. A pressure relief valve(s) maintains oil pressure in the galleries and returns oil to the oil pan upon high pressure. The oil galleries distribute the oil to all the bearing surfaces in the engine.

Once the oil has cooled and lubricated the bearing surfaces, it flows out of the bearing and gravity-flows back into the oil pan. In medium to large diesel engines, the oil is also cooled before being distributed into the block. This is accomplished by either an internal or external oil cooler. The lubrication system also supplies oil to the engine's governor.

Pistons & Rings

• Premium quality pressure die cast Aluminum Pistons and Cast as well as forged rings
• manufactured under stringent supervision.
• In house production of Centrifugally cast Ni resistant Rings.
• Material Standard LM 13 for Pistons and S G Iron and stainless steel Rings
• Material analysis, Pressure test, Tensile and Fatigue tests, Hardness, Thermal shock and expansion and profile tests are carried out for pistons and Rings.
• Piston Pins are manufactured with 20 Mn Cr5 material with hardening process to achieve the case hardness of 52-58 Hrc
• Wide Range available and development capacity of any Pistons and Rings upon samples.
• Capacity of supplying 25000 pistons and Ring sets per month

Diesel Engine Cylinder Liner

Diesel Engine Cylinder Liner

1. Function of cylinder liner
1) Formed cylinder working space with cylinder cover and piston.
2) Cylinder liner of trunk piston diesel withstands side thrust of piston, so it becomes lead of piston reciprocating action.
3) Transmit heat of piston assembly and self-heat to cooling water to keep its proper working temperature.
4) Cylinder liner of two stoke diesel engine is equipped with vent; it is hoisted by piston to achieve air distribution.
2. Working condition
Inside cylinder liner is directly affected by high-temperature and high-pressure gas, and always produce high-speed slide friction with piston rings and piston skirts. While its outer touch with cooling water, producing serious thermal stress under big difference in temperature and corroded by cooling water. Side thrust from piston not only acerbates inside friction of cylinder liner, but also makes it bent. When side thrust changes its direction, piston will strike cylinder. Besides, it has to withstand high installation preload.
Gas pressure make cylinder face produce tangential tensile stress and radial compressive stress, which is maximal inside, this kind of stress is radio frequency pulsating stress.
Serious thermal stress produced by difference in temperature between inside and outside of cylinder face, so, under normal temperature, inside wall produces compressive stress while cooling face produces tensile stress. But under extremely high temperature, metal of inside wall will be distorted and form residual stress when cooling. This low frequency caused by engine starting and stopping will make the material tired.
3. Requirements
Diesel engine cylinder liner should be with high strength, hardness, heat-resisting and abrasion-proof property. Smooth lubrication and cooling should be available during working.
Cylinder liner usual uses wear-resisting cast iron alloy including phosphor or boron as its material, such as HT25-47、HP-CuCrMo, etc. Inside cylinder liner sometimes is in process of chrome plating (spongy chromium plating, oil stored chromium plating), nitrogen and phosphorization to improve wear-resisting performance. Inside temper must be bigger than HB200 and fit well with piston ring temper; proper roughness with oil storing ability and running-in characteristic; with enough roundness and cylindricity precision to assure position accuracy between installing bearing face and central inner hole.

Crankshaft

Due to its nature of operation, there are several types of forces which come to act upon the crankshaft of engines used in marine propulsion. You will get a better idea about these forces if you take a close look at the image shown below which shows the various twisting and bending forces.

As can be seen from the figure, these forces are due to a variety of factors including but not limited to the weight of the pistons, combustion loads, the axial load from the propeller which is immersed in the sea, compressive loads of webs on journals and so forth.

Most of these forces have alternating patterns which gives rise to fatigue and the materials used for construction need to have substantial Ultimate Tensile Strength. Apart from that the other properties required in the material of a crankshaft are wear resistance, tensile strength, and ductility.

The material for construction also depends on the speed on the engine and slow speed marine diesel engines have crankshafts fabricated out of plain carbon steel with a percentage of carbon lying between 0.2 & 0.4%, while the alloy steels are used for engines having a relatively higher speed.

Fabrication of Crankshaft

Crankshaft manufacture is a complex and elaborate process and the exact procedure would vary with the type and size of the crankshaft under consideration but a few things would be good to know

• Fully-built Crankshafts are those in which all the various components are shrink-fitted after separate fabrication

• Semi-built Crankshafts are those in which several parts such as crank-throw and pins are case out of a single piece.

• Welded Crankshafts are those in which the crank-shaft is made by welding case web crank pins and half journal units.

• Flanged Coupling Crankshafts are made out in two pieces joined together by flanged couplings

There is a lot more to learn about marine diesel engine crankshafts which we will study in the next article such as taking crankshaft deflections.

References

Image of Forces on Crankshaft - Marine Engineering Knowledge by Brian

Image of Stresses on Crankshaft - Sanyal, D.K. (1998) Principles & Practice of Marine Diesel Engines. Mumbai: Bhandarkar Publications.

Engine Bed Plate

Introduction

A solid foundation is necessary for any structure, be it on the ground or meant for the sea. No doubt this axiom applies equally well to marine diesel engines which are huge and gigantic structures and have a lot of forces apart from their weight, such as the reactive forces when the huge piston rush up and down through the cylinders. It goes without saying that a very strong base is required to support such load and forces and the bedplate of the engine servers as the structural base of the engine. It acts as housing for the huge crankshaft while it also supports the cylinder block. In this article we will see about the role and functions of the bedplate and learn about its usefulness and purpose.

The Bedplate

If you want to get an idea about the magnitude of weight which is being supported by the bedplate as well as have a general idea about the size of a marine engine just take a look at the picture below. You will notice a red coloured circle with a pointer and that is meant to highlight a human being standing next to the engine. This will surely give you an idea about the size and magnitude of the marine engine.