3- Internal Combustion Engines cooling and lubrication system (automobile engineering)

 in the previous sections we had discuss :

Classification of Internal Combustion Engines and Engine Components (Course)

Internal Combustion Engines Components 2 (Course)

 





In This  section we will discuss :
-Describe and explain the operation of a typical cooling system for an industrial ICE.
-Describe and explain the operation of a typical lubrication system for an industrial ICE.


SECTION 3

Objective 7
Describe and explain the operation of a typical cooling
system for an industrial ICE.


ENGINE COOLING

Small internal combustion engines are often air-cooled. Each cylinder or motor
block is equipped with many thin fins creating an extensive cooling surface. This has the
advantages of being simple and cheap, but the disadvantage of lack of control of the engine
temperature

because the cooling efficiency depends on the weather conditions. For high
compression diesel engines, the combustion temperature can exceed 2000°C, and
only 30 - 35% of the heat is converted to mechanical work, leaving 65 - 70%,
which must be removed. A small part of the heat is removed by radiation but the
bulk of it is removed by cooling water circulating through the water jackets of
the cylinders andthe valves in the cylinder heads. Fig. 25illustrates the
location of the cooling waterjackets to the cylinders for heat removal.


Radiator Cooling Water System

Most engines are water-cooled and use a radiator to cool the water (coolant).
The radiator is an air-cooled heat exchanger, which cools the coolant (a water/glycol mixture)
before it is pumped back through the engine. Fig. 27 shows this type of system. The system is
run at a positive pressure of around 100 kPa. This increases the boiling point of the
coolant, and reduces the likelihood of the coolant boiling. The radiator cap or pressure cap
maintains the pressure on the system. It will open under high pressure and allow air in the
system if a vacuum is present. The engine normally drives the water pump and the fan for the
radiator airflow.

The water temperature is controlled by a thermostat, which is located in the
cylinder head, between the head and the radiator. It opens up and allows more water to flow as
the water temperature increases. When the engine is cold the thermostat is nearly closed.


The cooling water system for a diesel engine, like the one illustrated in
Fig. 26, is shown in Fig.27. It consists of a closed engine water system with circulating pump,
expansion surge tank, and shell-and-tube heat exchanger. Engine coolant flows through the shell
side of the exchanger, while cooling tower water flows through the exchanger tubes. With
this closed system, the coolant can be treated and topped-up with ethylene
glycol for corrosion and frost protection.


To obtain the most even engine cooling, the coolant circulation through the
engine is kept at its maximum flow rate. The coolant temperature is controlled (usually between 60  and 75°C)

by regulating the flow of water from the cooling tower.
An expansion tank, with a makeup valve, allows the engine cooling water to
expand safely.

(Note - to simplify the sketch, the suction and discharge valves for the pumps
have been omitted.)

The engine may drive the engine water pump or it may be electrically driven. The
advantages of a separately driven, electric pump are that it can be kept running after the
engine is shut down to prevent high temperatures, and by delaying the start of the pump, the
oil temperature can be rapidly increased to operating temperature at start-up.

The pistons of large diesel engines cannot dissipate heat rapidly enough without
piston cooling. The piston is oil-cooled, using oil from the lubricating system. The
oil is delivered to the piston through telescopic pipes or swinging elbow pipes, and returned the
same way. A weak point of large slow speed engines is the telescopic and elbow pipes. A
solution to that problem is the crosshead engine. Here the piston cooling oil is circulated from
the crank to the crosshead through a channel in the piston rod to the piston, then back
through a second channel in the piston rod to drain out at the crosshead.

Thermostat
The function of the thermostat is to sense eI1gine temperature and control it by
controlling coolant flow. Coolant flow is divided in the thermostat housing. The coolant may
flow to the radiator for cooling or back to the water pump suction via the bypass tube for
recirculation back to the engine. The purpose of the bypass tube is to reduce warm-up time and
prevent the cylinder head from overheating when the thermostat is closed. Natural convection
currents carry the coolant through the bypass when the engine is shut off and hot. There
are several

types of thermostats:
• the bellows type, which are not common;

• the wax pellet type, which is the most common and has accurate temperature
control.

This type uses copper impregnated wax as an expansion material and is not
sensitive to pressure.

NOTE:
Always install a thermostat with temperature sensor facing towards the engine



Inspection and Service of the Cooling System

Cooling System Problems

Several problems can cause cooling systems to lose their effectiveness.

These are:

• Deposits of mineral scale, which are hard and insoluble. These can collect
on the inside of the cooling system and reduce the system's ability to transfer heat.
The scale acts like an insulator. Scale tends to form in the areas of greatest heat
transfer. Soft slime or gel-like coolant fouling deposits can form in quiet flow areas, such as
the lower sleeve bores. These problems are combated with proper coolant inhibitors.

• Corrosion occurs when the metal combines with oxygen to form rust. This is a
natural process and is reduced by using inhibitors in the coolant. The coolant should
also be checked for its pH value to determine whether it is acidic or alkaline.

• Cavitation is a mechanical or physical problem that causes the erosion of a
material due the repeated collapse of vapour pockets developed by liner expansion and vibration. Cavitation can occur in any type of material and is not limited to
the cooling system. This problem is common on cylinder liners. It is partially
combated by pressurizing the cooling system, inhibitor packages, and by plating the
liners.

• Overheating is caused by a wide variety of conditions. Some of these
conditions are: low coolant, scale build-up, the thermostat not opening or only partially
opening, and lack of circulation due to water pump failure. Cracked heads can result from overheating and in turn cause overheating by pumping air and exhaust into the coolant, which reduces its ability to remove heat.

• Aeration of the coolant can be caused by from the water pump sucking air or by cracked heads. Air in the coolant does not transfer heat very well and causes
hot spots in the engine. Coolant leaks will be obvious if they are on the outside of the
engine and are generally easy to fix. These can be pipe or water pump leaks. Water
pumps are equipped with a weep hole that is located before the pump bearing and which

indicates that a seal is leaking. This keeps the coolant out of the engine oil.
Some leaks are not so obvious and take considerable effort to determine the problem.
This includes cracked heads, liner O-ring leaks, or liner cavitation leaks. Engines
equipped with water-cooled exhaust manifolds and water-cooled turbochargers can develop leaks.


CAUTION

If freeze plugs (safety plugs) were removed during flushing of the coolant
passages new ones should be installed.

Component Inspection

Water Jackets

Water jackets can only be properly cleaned of scale during overhauls. Flushing
the block is beneficial and removes some of the softer deposits.


Thermostats

All thermostats should be tested before installation. This ensures fewer
problems later. Thermostats must be fully closed at room temperature. The temperature is stamped  on the thermostat. Heat the thermostat in a solution and use a thermometer to check the opening and fully open temperatures.



Water Pumps and Drives

The water pump should be rebuilt at every overhaul to ensure that there is less
downtime between overhauls. This includes installation of new mechanical seals and
bearings. The drive mechanism can be belt, chain, or gear and should also be checked, adjusted or repaired at every overhaul.


Coolant

The coolant may require changing or replenishing of additives to ensure that it
will not be harmful to the rest of the system.

Heat Exchangers and Expansion Tanks
These can be cleaned both inside and out to ensure that there is good heat
transfer and no leakage.


Radiator Caps
Pressure caps can be checked for leakage and for the correct pressure. Defective
radiator caps can lead to overheating.


Coolant
Water is a good coolant and absorbs approximately 15% more heat than mixed
glycols. However, water has some shortcomings. It does not provide protection for cold
weather operation and does not inhibit rust or corrosion. Additives can be added to
inhibit rust and corrosion. Water can also be mixed with other materials to resist freezing.
Water has a boiling point that is limited to 100ºC (212 ºF).

There are three coolant products available that will add freeze protection.
Industrial-type glycols are available in some plants. .Be careful: industrial glycols may not
contain inhibitors and must have them added to the solution. Glycols without inhibitors are more
corrosive than water. It is also recommended that glycol be mixed in a 50/50 solution with
water by volume, which provides the best freezing and boiling protection. Glycols that are
formulated for cooling systems have inhibitors added to them.


• Alcohol-Based Coolants
Alcohol-based coolants do not have a very high boiling point, but are easier on
the engine bearings if a liner leak occurs and the coolant gets into the oil.


• Ethylene Glycol Based Coolant
Ethylene glycol is the most commonly used coolant and has been used for many.
years. It has a high boiling point (approximately 3200P unmixed or 2300P in a 50/50
solution) and has a low viscosity at lower temperatures. The disadvantages of ethylene glycol
are that it is toxic and can damage engine bearings when it leaks into the crankcase.
Propylene glycol can be used in place of ethylene glycol.


• Propylene Glycol Based Coolant
Propylene glycol recently came on the market to replace ethylene glycols, which
are more toxic. Propylene glycol has some advantages in reducing cavitation, but causes
some plastics and elastomers to swell at higher temperatures. This could cause
problems with liner a-rings and water pump seals if the materials are not compatible with this
product.





Objective 7

Describe and explain the operation of a typical lubrication system for an
industrial ICE.



LUBRICATING OIL SYSTEMS

The importance of proper lubrication is obvious, as the majority of operating
problems and damage to internal combustion engines are caused by improper lubrication
control. The lube oil forms a film around the shafts, separating the shafts and bearings to
prevent metal-tometalcontact, thus reducing friction and preventing wear of the bearing metal. The heat due

to friction in large bearings can be considerable, and large quantities of oil
have to be circulated through the bearings for temperature control.


Typical lubrication system for a medium sized diesel engine is shown in Fig.
32. It is a forced-feed system of lubrication and uses the oil contained in the bedplate as
a reservoir. A gear type oil pump is driven from the crankshaft. Fig. 33 shows a gear type of
oil pump. The oil enters the pump and is carried around the pump casing by the gear teeth. It
is then discharged. The oil is prevented from returning to the inlet by the meshing of
the gear teeth. Oil is pumped from the bedplate through an oil filter and cooler into the
lubricating oil manifold. A separate pipe supplies oil to the turbocharger. A supply of cooled
oil is critical for the turbocharger to lubricate the high-speed bearings and to carry heat away
from the rotor.

Connections from the pressure manifold go to each of the main, camshaft, and
governor bearings and to the camshaft driving chain. Oil is also sent to the gear
housing, the injection pump, and the gear housing. Oil is also led via the connecting rods to the
small-end bearings.

The pistons also receive some oil for cooling in this design.


The temperature of the oil leaving the cooler is used to control the engine
oil temperature. Fig. 32 also shows a separately driven oil pump. A system with two separately
driven pumps is often used on large engines to give full oil pressure during starting and
stopping. This simplifies the engine because the oil pump and gears are omitted.

The cylinder, or internal, lubrication of medium and large size diesels is
applied at two, three, or four points on each cylinder. Each location is supplied by a small plunger  pump with adjustable stroke, located in a central lubricator, with one to twelve such
pumps operated by cams on a common camshaft.
The cylinder lubrication of smaller engines is generally “splash lubrication”
(Fig.33). The crankshaft rotates partly immersed in oil. Oil is thrown from the crank into the
skirt of the piston, and flows down inside the piston and through holes drilled in the piston
into the groove for the lower piston ring (Fig.30) and seeps in over the top of the
piston ring to the cylinder walls. On the down stroke, the lower piston ring scrapes the cylinder
walls. Excess oil drains through holes just below the ring back to the inside of the piston.


With splash lubrication the same oil is used for bearing and cylinder
lubrication and it is very important that only the oil recommended by the manufacturer be used.

For large engines with separate cylinder lubrication, oils designed for very
high temperatures and designed to withstand combustion products are used and give better
lubrication. The bearing lubrication can also be improved, as oils designed for this use only can
be used. With the splash system, the oil used is a compromise between bearing and cylinder
lubricants. Fig. 34 shows the lubrication system for a six-cylinder diesel engine. It has
a dual type oil filter, and a shell and tube type of oil cooler. The oil cooler uses cooling
water to cool the oil. The oil supply piping to the camshaft and crankshaft can be seen in the figure.



Engine Oil Properties and Selection
The engine oil must be matched to the application and to the engine's operating
conditions; therefore, engine oil selection is very important. Diesel engines must use the
oils specified by the manufacturer. Natural gas and other gaseous fuel engines do not use the same oils as diesels.

Natural gas engines that operate continuously should use SAE 30 or 40 weight
oil. There is a difference in the oils recommended for naturally aspirated engines and for
engines with turbochargers. Most turbocharged engines use oil with an ash content between 0.5
% and 1.0 %. Some oils are recommended for engines that burn sour fuel. Multigrade oils
are usually not recommended unless the engine is in a harsh environment and is not
continuously in operation. .


Inspection and Service of the Lubricating System
Oil Contamination and Change Interval
The oil change interval varies considerably among the wide variety of industrial
engines

available. Following are some of the considerations that affect oil and filter
changes.


• The type of fuel burned and the quality of the fuel.

Engines that burn gaseous fuels such as natural gas and propane sustain much
less oil contamination than engines using liquid fuels. In cases where there is H2S in
the gas, oil changes must be performed much more frequently.


• The environmental conditions in which the engine operates.

If the conditions .are very hot, dusty, or if there are other adverse
conditions, more frequent oil changes are necessary.


• The amount of oil in the sump and the extent of the filtration systems.
Some engines have very large capacity sumps and do not require oil changes
for very long periods of time. Some systems use a centrifuge oil filter and an engine oil
additive package. These additives are added to the oil to replenish additives used or
removed from the oil. When the centrifuge system is used the oil seldom needs to be
changed. An oil sample should be taken at the time of engine shutdown (or just prior) so
that the sediment does not have a chance to settle out before you obtain a sample.
Numerous labs are available for testing oil samples. Oil sample tests can be helpful in predictive
maintenance

NOTE
Lube oil analysis is used to determine the condition of the oil and wear in the
engine. It is recommended that samples for testing be taken at regular, scheduled intervals.

Oil Consumption
Oil consumption is normal in engines. This is due to the oil riding up the
cylinder walls to lubricate the piston rings and cylinder. Some of the oil reaches the valve
guides to lubricate the valve stems and is burned in the combustion chamber or exhaust. The amount  of oil that is consumed for the size of the engine is the main concern. Larger engines have more surface

area on the cylinders, which means that more oil is lost to the combustion
chamber. It is not unusual for an engine with a displacement of 6600 cubic inches to consume 2
gallons of oil in a 24-hour period. Oil consumption is also related to the amount of power
delivered by the engine. Engines under heavy loads consume more oil.

NOTE
The larger the engine the greater the amount of oil consumption expected.

Oil Pressure
Oil pressure is affected by several factors. The main conditions are the
viscosity of the oil, the amount of bearing clearance, and the volume of the oil pump. Any change in these conditions changes the oil pressure.


• Low oil pressure
One of the most common problems with lubrication systems is low oil pressure.

Before you do any repairs, a master oil gauge should be installed on the engine
to see if the gauge is faulty. The main causes include: not enough oil in the
crankcase, loose bearings, oil viscosity that is too low due to high-temperature operation, and
the oil pump relief valve being stuck open or having a broken spring. The viscosity of
the oil can also be changed by fuel or water dilution.


• Oil pressure too high
This is not a common problem. High oil viscosity, the relief valve set too high,
or blockages can cause high oil pressure in the system. When the engine is cold,
expect the pressure to be higher than normal, but it should not be excessive.
Excessive pressure can rupture oil filters and even wash out bearings if allowed to
continue for extended periods of time.



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