In this article we will discuss about:- 1. Cooling System in IC Engines 2. Lubrication System in IC Engines 3. Governing System.
Cooling System in IC Engines:
There are mainly 2-types of cooling systems:
1. Air Cooled System:
Air cooled system is generally used in small engines say upto 15-20 kW and in aeroplane engines.
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:
(i) Amount of air flowing through the fins
(ii) Fin surface area
(iii) Thermal conductivity of metal used for fins.
Advantages of Air Cooled System:
Following are the advantages of air cooled system:
(a) Radiator/pump are absent hence the system is light.
(b) In case of water cooling system there are leakages, but in this case there are no leakages.
(c) Coolant and antifreeze solutions are not required.
(d) This system can be used in cold climates, where if water is used it may freeze.
(a) Comparatively it is less efficient.
(b) It is used in aeroplanes and motorcycle engines where the engines are exposed to air directly.
2. 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 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:
(i) Thermosiphon 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.
(ii) 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.
Advantages and disadvantages are given as following:
1. Uniform cooling of cylinder, cylinder head and valves.
2. Specific fuel consumption of engine improves by using water cooling system.
3. If we employ water cooling system, then engine need not be provided at the front end of moving vehicle.
4. Engine is less noisy as compared with air cooled engines, as it has water for damping noise.
1. It depends upon the supply of water.
2. The water pump which circulates water absorbs considerable power.
3. If the water cooling system fails then it will result in severe damage to engine.
4. The water cooling system is costlier as it has more number of parts. Also it requires more maintenance and care for its parts.
Lubrication System in IC Engines:
The functions of lubrication system are to provide a sufficient quantity of filtered oil to all moving parts.
There are 3 basic types of lubrication systems:
1. Petrol or Mist System of Lubrication:
In this system, lubricating oil will be added to petrol tank only i.e., it is mixed in the petrol in a definite proportion (i.e., generally 30-60 ml/litre e.g., Bajaj scooters, M-80, Luna, Pride etc.). Lubricating oil particles will go to engine cylinder and various parts for lubrication along with air fuel mixture.
The various parts to be lubricated are as under:
Parts of IC Engines which requires lubrication are:
(3) Piston rings
(4) Gudgeon pin
(5) Crank pins
(6) Main bearings
(7) Cam and cam shaft
(8) Timing gears
(9) Rocker arms
(10) Valves etc.
2. Wet Sump System:
These are used in relatively small engines. The bottom of the crankcase contains oil pan (sump) which acts as oil reservoir and oil cooler.
Oil supplied to different parts by 2 different methods:
(a) Splash Lubrication:
In this type, the oil from the sump is pumped to the oil trough which is located below the crank pins. The extended end of connecting rod known as dipper strikes the oil surface and splashes oil over various parts of engine. The oil returns to sump due to gravity.
(b) Pressure Lubrication:
This system mainly consists of a gear pump, oil strainer, oil gallery made up of copper tubing. In this system oil flows to different parts through the drilled passages in the crank shaft and connecting rod.
Oil pump draws filtered oil through the oil strainer and pumps it to the main oil gallery. From where it goes to the main bearings. After lubricating main bearings, lubricating oil will go to crank pin bearings through the drilled holes. And from the crank pin bearings, oil will flow to piston pin bearings through the oil hole drilled through connecting rod web. Small amount of oil is also sprayed on the cylinder walls to lubricate between cylinder walls and piston rings.
Cam shaft, valves mechanisms are lubricated through the separate lines.
3. Dry Sump System:
In this system the oil falling from various parts is removed by a scavenging pump. Oil passes through a filter and goes to the supply tank, oil is again pumped from the supply tank and supplied to various engine parts. Thus oil is prevented from accumulating in this base of engine.
This uses only forced (pressure) types feed system. A filter and strainer are used in the oil circuit to remove the foreign materials and impurities. In large, IC engines oil is cooled with the help of cold water to maintain its viscosity in the required range and to prevent it from lubrication.
Important Parts of a Lubrication System:
Following are the important parts of a lubrication system:
(a) Oil Sump:
It contains lubricating oil and it is the bottom most part of crank case. It is made out of casting.
(b) Oil Pump:
Oil pump is a pump which pumps lubricating oil to various parts to be lubricated. Generally oil pump will be a gear type pump. It consists of two inter meshing gears in a pump casing. When one of the gears is rotated, other gear will also rotate and the oil will be trapped in the pockets between the pump casing and gear teeth and oil will be pumped. It also consists of pressure relief valve to release pressures.
(c) Oil filters:
As the name implies oil filters are used in lubricating system to filter out the dirt particles.
Various types of oil filters are as under:
(i) Cartridge Type:
Cartridge type oil filter mainly consists of filter element enclosed in a casing as shown. The oil to be filtered enters from top, when it flows down it gets filtered and clean oil will go to main oil gallery, from where it goes to various parts for lubrication.
Filter cartridge element is cleaned oftenly or replaced if required during servicing.
(ii) Edge Type Oil Filter:
An edge type oil filter mainly consists of a central spindle to which a number of discs are attached as shown. Also there is a square rod having alternate discs attached. The clearance between the discs on central spindle and square rod is very small. When the impure oil enters from oil inlet and flows through the discs to oil outlet, impurities are collected in the clearance between the discs and clean oil comes out from oil outlet.
(iii) Centrifugal Type of Filter:
Centrifugal type oil filter mainly consists of a central hallows spindle, rotor casing, oil tubes, and stationary casing as shown.
Impure oil enters from oil inlet and flows to oil tubes through the spindle holes. From the oil tubes oil jets are issued under pressure. Oil jets when issued it impinges on the walls of stationary casing and rotor starts rotating, pure oil gets separated and comes out from oil outlet.
(d) Oil Strainers:
It consists of a wire mesh. It prevents any impurities from entering the oil pump.
Governing System in IC Engines:
Governor is the mechanism or device used to maintain constant speed irrespective of changes of load on the engine. And the method of maintaining constant speed is called as Governing.
There are three distinct methods adopted for varying the power of the engine in sympathy with the action of governor, these methods will again differ in the mechanical means adopted in regulating the power. In all the cases the ordinary centrifugal governor is used for controlling the mechanical devices.
The following is the usual classification adopted for the various methods of governing:
(a) Hit and Miss Governing:
In this type of governing, the action of the governor causes the fuel inlet valve to remain closed during a cycle so that no fuel is admitted. The engine will thus perform an idle cycle. Or in other words, when the engine speed increases beyond certain limit, the combustion is missed for a few cycles by preventing the charge to enter into the cylinder. So the engine runs idle for few cycles.
It results into the following two disadvantages:
1. Efficiency decreases because of idle cycles along with actual working cycles.
2. Since the combustion is missed during same cycles, it produces very uneven turning movement for the crank shaft.
The hit and miss method of governing is in common use in small gas engines, and is actually quantitative governing.
In small, light oil engines the hit and miss mechanism operates on the exhaust valve and prevents it opening when the speed is too high; the burnt gases are thus retained in the cylinder and are alternately compressed and expanded until the speed is reduced.
(b) Quantitative Governing:
This method varies the power of the engine by regulating the quantity of mixture (fuel and air) which enters the cylinder. This is sometimes done by throttling the mixture before it enters the cylinder, the movement of the throttle valve being regulated by the lift of the centrifugal governor. Another method of quantitative governing, used in gas engines, is by varying the lift of the inlet valve, and thus reducing the quantity of mixture entering the cylinder.
So, as discussed above, generally centrifugal types of governors are used.
Cylindrical part is the air horn and the narrowest cross-section of which is the venturi. Throttle valve is provided to regulate the amount of charge (air + fuel mixture) entering the engine cylinder. Throttle valve is connected to the Governor as shown.
Now when the load on the engine increase, the speed of the engine decreases and because of reduced speed, fly weights move inwards (shown by dotted arrows) and the sleeve moves downwards. Then its opens the throttle valve more and hence more charge enters the engine cylinder to develop more power and to bring engine speed constant.
And when the load on the engine decreases—speeds increases—fly weights move outwards (shown by arrow) — closes the throttle valve accordingly—reduces the supply of charge. Hence the engine develops required less power and maintains constant speed.
(c) Qualitative Governing:
In this method of governing the strength of the mixture is altered by the action of the centrifugal governor, thus varying the quality of the mixture. This is done by regulating the amount of fuel entering the cylinder, air supply remaining constant. This method of governing is used in all heavy oil-engines using pure air compression.
The amount of fuel entering the cylinder is varied by the action of the governor. It may vary the stroke of the oil pump or it may by pass part of the fuel back to the oil tank or it may delay the closing of the suction valve of the fuel pump. All of these methods will cause a variation in the point of cut off.
Following are the important centrifugal governors:
(i) Watt Governor (Simple Conical Governor):
It is named after Watt, when the load decreases-speed increases fly weights move outwards as shown by arrows and lift the sleeve. On the other hand when the load increase speed decreases, weight move inwards (shown by dotted arrows) and sleeve moves downwards. (Fig. 32.2)
(ii) Porter Governor:
If the central load is provided on the sleeve then watts governor is called its Porter Governor.
(iii) Proell Governor:
In this governor fly weights are provided on the extension of lower links as shown and it contains central load.
(iv) Hartnell Governor:
It mainly consists of 2-bell crank levers and compression spring as shown. To the one end of bell crank levers, fly weight is provided and other end rollers. The levers are pivoted at O. When the speed increases fly weight move outwards and the lever which is provided at O lifts the rollers and sleeve against the compression of spring.
(v) Spring Controlled Governor of Gravity Type:
Figure 32.6 shows spring controlled gravity governor. It mainly consists of 2-bell crank levers. They are provided with rollers at one end and fly weights at the other. Rollers will be resting over the cap which forms top end of shaft. Under the cap spring is provided as shown.
When the load decreases, speed increases and fly weight move outwards and the other press cap which in turn compresses the spring.
Used in Petrol engines, Diesel engines, Steam engines and Steam turbines etc.