Engine Cooling And Lubrication

Engine Cooling During combustion of fuel tremendous amount of heat is produced. 35% of Engine Heat has to be carried through Cooling System

Absence of adequate cooling causes Piston seizure Breakdown of lubricating oil film Over heating of valves and bearings

Purposes of Engine Cooling To prevent the development of high temperatures in the combustion chamber thereby saving damage of various engine parts and the oil which lubricates them To maintain the operating temperature at a safe level over a wide range of speeds, loads and ambient temperatures To help in warming up the engine to the required operating temperature as rapidly as possible and then maintain that temperature irrespective of the outside temperature as rapidly as possible

Types of cooling system Air cooling system Water cooling system Liquid cooling system Steam cooling system

Air cooling It is used in aero planes and motorcycle engines where the engines are exposed to air directly. In this system fins or extended surfaces are provided on the cylinder walls, cylinder head etc, Heat generated due to combustion in the engine cylinder will be conducted to the fins and when the air flows over the fins, heat will be dissipated to air.

The amount of heat dissipated to air depends upon : (a) Amount of air flowing through the fins. (b) Fin surface area. (c) Thermal conductivity of metal used for fins.

Advantages of Air Cooled System (a) Radiator/pump is absent hence the system is light. (b) No leakage problem. (c) Coolant and antifreeze solutions are not required. (d) This system can be used in cold climates i.e, if water is used it may freeze. Disadvantages of Air Cooled System (a) Comparatively it is less efficient. (b) Air cooled system is generally used in small engines of 15-20 kW

WATER COOLING SYSTEM

In this method, cooling water jackets are provided around the cylinder, cylinder head, valve seats etc. The water when circulated through the jackets, it absorbs heat of combustion. This hot water will then be cooling in the radiator partially by a fan and partially by the air flow developed by the forward motion of the vehicle. The cooled water is again re-circulated through the water jackets.

Types of Water Cooling System There are two types of water cooling system, Thermo Siphon System In this system the circulation of water is due to difference in temperature (i.e. difference in densities) of water. So in this system pump is not required but water is circulated because of density difference only. Pump Circulation System In this system circulation of water is obtained by a pump. This pump is driven by means of engine output shaft through V-belts.

Components of Water Cooling System

Water cooling system mainly consists of : (a) Radiator, (b) Thermostat valve, (c) Water pump, (d) Fan, (e) Water Jackets, and (f) Antifreeze mixtures.

Radiator It mainly consists of an upper tank and lower tank and between them is a core. The upper tank is connected to the water outlets from the engines jackets by a hose pipe and the lower tank is connected to the jacket inlet through water pump by means of hose pipes. There are 2-types of cores : (a) Tubular (b) Cellular

Thermostat Valve It is a valve which prevents flow of water from the engine to radiator, so that engine readily reaches to its maximum efficient operating temperature. After attaining maximum efficient operating temperature, it automatically begins functioning. Generally, it prevents the water below 70°C.

Figure shows the Bellow type thermostat valve which is generally used. It contains a bronze bellow containing liquid alcohol. Bellow is connected to the butterfly valve disc through the link. When the temperature of water increases, the liquid alcohol evaporates and the bellow expands and in turn opens the butterfly valve, and allows hot water to the radiator, where it is cooled.

Water Pump It is used to pump the circulating water. Impeller type pump will be mounted at the front end. Pump consists of an impeller mounted on a shaft and enclosed in the pump casing. The pump casing has inlet and outlet openings. The pump is driven by means of engine output shaft only through belts. When it is driven water will be pumped.

Engine Lubrication Principles of Engine Lubrication Primary purpose is to reduce friction No metal to metal contact occurs - Cushioning Friction and abrasive wear held to a minimum To absorbs shocks To prevent the deposition of carbon, soot and sludge To act as cooling medium To form a good seal between piston rings and cylinder walls Cleans the engine parts

Lubricating Systems The different systems for lubricating automobiles are: Petroil System Pressure System Semi Pressure system Splash System Dry sump System Wet sump System

Petroil System This system is Simplest one Commonly used in two stroke petrol engine In this type certain amount of oil is mixed with fuel generally 2 to 3% This proportion must be proper. If this proportion is less, danger of oil starvation causes damage to engine. If this proportion is more engine gives dark smoke and excessive carbon deposits on the cylinder head.

Splash System It consists of a scoop fitted at the lower end of connecting rod as shown in the figure. As the engine runs scoop splashes the oil from trough by centrifugal force to all engine parts.

Pressure-Lubrication A mechanical pump supplies oil under pressure to the bearings throughout the engine. Pressure is around 200-400kPa

Advantages of pressure lubrication system Positive introduction of oil to the bearings. Cooling effect caused by the large quantities of oil which can be circulated through a bearing.

Semi-pressure lubrication System In this type of lubrication system oil pressure between 0.4 to 1 Kg/cm2 In this some parts like cylinder wall, piston, piston pin, Connecting rod are lubricated by splash system some are by pressure system Dry Sump Lubrication System This consist of two pumps One scavenging pump placed below the Sump, other pressure pump placed at the tank Scavenging pump supplies lubricating oil to main tank through filter and pressure pump supplies oil to the different parts of the engine through oil cooler Pressure of the oil is around 4 to 5 Kg/cm2 Here sump is kept dry

Dry Sump Lubricating System

Wet Sump Lubrication Here oil is delivered at a pressure around 4 to 5 Kg/cm2 from sump stainer to different parts of the engine. After lubrication lubricating oil is drawn back into the sump Here oil is always present in the sump. Hence the name wet sump lubrication.

Wet Sump Lubrication system