World of Mechanical Engineering

Parts of Steam Engine and Its Functions.

noreply@blogger.com (MechanicalGuru) — Wed, 24 Jun 2009 16:42:00 +0000

Steam engines are used very widely in engineering up to 1930 for generation of power but after it are replaced by internal combustion engine. Diesel engine, petrol engine are the common example of internal combustion engine. Steam engines are widely used on ships in old days at present they are replaced by diesel engines. To disclose some more important information about this old machine, I am giving some details about its parts and their functions in operating.

01) Frame: -
It is the heavy casting which supports all the stationary and moving parts of the engine and holds them in proper alignment. It requires foundation to rest upon or engine bed plate fixed on engine foundation.

02) Cylinder: -
It is the cast iron cylindrical hollow vessel in which the piston moves to and fro under the pressure of steam. Crank side end and outer end of cylinder is closed by end covers and made steam-tight.

03) Steam Chest: -
It is the closed chamber integral with the cylinder. It supplies steam to the cylinder with the movement of slide valve.

04) Stuffing Box and Gland: -
This part is fitted on the crank end cover of the cylinder and their function is to prevent the leakage of steam past the piston rod.

05) Piston: -
It is the cast iron cylindrical disc moving to and fro in the cylinder under the action of the steam pressure. This part converts heat energy of steam into mechanical work. Cast iron piston rings make the piston steam tight in the cylinder and thereby prevent the leakage of steam past the piston.

06) Cross head: -
It is the link between piston rod and the connecting rod. It guides the motion of the piston rod and prevents it from bending.

07) Connecting Rod: -
It is cast iron part which helps to convert reciprocating motion of piston into rotary motion of the crank. Gudgeon pin is used to connect one end of connecting rod to cross head and its open end is connected to the crankshaft.

08) Crankshaft: -
It is made from mild steel on which flywheel is mounted on it. It is supported on the main bearings of the engine and it is free to rotate in them.

09) Slide Valve: -
Fixed on the steam chest and its function are to admit the steam from steam chest to the cylinder, and exhaust the steam from the cylinder at the proper moment. The valve gets to and fro motion from the eccentric fitted on the crankshaft.

10) Main Bearings: -
This part support crank shaft and fitted in the engine frame known as main bearing journal.

11) Flywheel: -
It is made from cast iron or cast steel and mounted on the crankshaft to prevent the fluctuation of engine speed throughout the stroke and to carry the crank smoothly over the dead centers.

12) Governor: -
To control the speed of the engine according to the load conditions, the governor is used. The speed of the engine is controls either by the quantity or pressure of the steam supplied to the engine.

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Important Characteristics in formation of Steam.

noreply@blogger.com (MechanicalGuru) — Tue, 23 Jun 2009 15:20:00 +0000

When any liquid is heated at constant temperature, it starts changing in vapour condition. A vapour is a mixture of gas and liquid particles in suspension and it can be liquefied by moderate changes of pressure or temperature. The process of vapour formation from liquid state has some definite characteristics to follow,

Characteristics of Steam formation.

01) The heat supplied during the process of vapourization changes its state gradually from liquid to gaseous state.

02) The vapour is said to be dry saturated when the process of vapourization takes place at constant pressure and temperature. In other word we can say when the liquid is completely evaporated it is called dry saturated.

03) The vapour is called superheated when the heat is added to the dry saturated vapour state. At superheated state, the temperature will rise gradually.

04) During the process of superheating a vapour at constant pressure, the volume will increase approximately in proportion to the absolute temperature, which indicates that the vapour is approaching the state of perfect gas.

05) The temperature at which the evaporation process is taking place is increase when the pressure on the liquid surface is increased

06) The latent heat of vaporization decrease with the increase of pressure and temperature but the sensible enthalpy increases under this condition.

07) The total heat (Enthalpy) of dry saturated vapour increases with increase in saturation temperature. In lower range of pressure and temperature, the rate of increase in sensible enthalpy is greater than the rate of decrease in latent enthalpy with the increase in pressure.

After certain saturation temperature the rate of increase in sensible enthalpy is less than the rate of decrease in latent enthalpy and hence, the enthalpy of dry saturated vapour decreases. This will continue to happen until the saturation temperature is reached when the latent enthalpy becomes zero and the enthalpy of dry saturated vapour becomes equal to the sensible heat.

This saturation temperature is called as critical temperature and the corresponding pressure is called critical pressure and the state of substance is called its critical state.

08) Steam can not exist as saturated vapour above its critical temperature. At any temperature higher than the critical temperature (374.14 degree centigrade) the vapour can only exist as a gas without any effect of pressure.
At critical temperature, the specific volume of dry saturated vapour becomes equal to the specific volume of the liquid from which it is being formed.

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Various Important Properties of Substance.

noreply@blogger.com (MechanicalGuru) — Mon, 22 Jun 2009 17:12:00 +0000

State means the exact condition of a substance and the variables which determine the state are known as properties. These properties are sub-divided into principal properties and fundamental properties. Fundamental properties are,

01) Pressure
02) Volume
03) Temperature

Above properties are also known as basic properties as they may be found out by direct observation or simple measurements. You will found details about these properties as below,

01) Pressure: -It is the force applied over a unit area. In international system (SI) of units, the unit for pressure is the force of one Newton (N) acting on a square meter area which is known as Pascal (Pa) so,

1 Pa = 1 N/meter square
1 Kilo pascal = 1000 Pa = 1 KPa
1 Mega Pascal = 10, 00,000 Pa = 1 MPa

Other unit for pressure is bar and atmosphere pressure (atm.)
Gauges are used to measure the pressure of fluid. Pressure gauges which used to measure

The pressure which is greater than atmosphere where as the vacuum gauges is used to measure pressure less than atmospheric pressure. The absolute pressure in pressure gauge is equal to the observed gauge pressure plus the atmospheric pressure where as the absolute pressure in vacuum gauge is equal to atmospheric pressure minus the vacuum.

02) Volume: - It is the space which the given substance occupies and it is measured in cubic meters. The most known unit of volume is liter.

The specific volume of a substance is its volume per unit mass and generally expressed in cubic meter per kilogram of air at zero degrees centigrade and under a pressure of 760 mm of mercury has a volume of 0.7734 cubic meters. Therefore, the specific volume of air under this condition is 0.7734 meter cube per kilogram.

The density of substance is its mass per unit volume is generally expressed in kilogram per cubic meter. So, under same conditions of pressure and temperature, if the specific volume of air is 0.7734 meter cube per kilogram then its density is 1.293 kilogram per meter cube.

03) Temperature: - It is the measurement of hotness or degree of coldness of a given substance.

Ordinarily temperatures are measured by thermometers, high temperatures are measured by pyrometers, small and precise changes of temperature can be measured by resistant thermometers and thermocouples.

In centigrade thermometer the freezing point of water is marked as zero and the boiling point as 100 at the atmospheric pressure, these points are called as fixed points of a thermometer.

Absolute zero is the temperature at which the internal energy of a substance becomes zero. The measurement of temperature taken above the absolute zero is known as absolute temperature and expressed in degrees of Kelvin scale or K.

The exact relationship between Kelvin scale and Celsius scale is,

Temperature K = Temperature degree centigrade + 273.15

I hope the above important information will help you to understand about some fundamental properties.

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How to Inspect Steam Boiler by Different Ways?

noreply@blogger.com (MechanicalGuru) — Sat, 20 Jun 2009 15:13:00 +0000

For power generation through steam turbine or steam engine, steam is required. Steam is also required for industrial process work, hot water supply and heating installations etc. This steam is produced with the help of utility called boiler.

A boiler is a closed vessel where combustion of fuel produces heat to convert water into steam at the desired temperature and pressure.

For the safe operation of boiler, it should be inspected by various methods and at various stages. You will find some important information on boiler inspection from below description.

01) Inspection before registration:-
Every new boiler must get registration from government authority so this is the first inspection carried out on new boiler. For this inspection boiler is completely stripped off all its mountings, coverings etc. Each and every part is carefully examined for defects due to design, workmanship or transportation. If any defects found, these are noted in the registration book.

The working pressure of the boiler is fixed after testing its various parts and a certificate is issued for the results obtained. After various satisfactory tests, the boiler is registered and a registration certificate is issued.

02) Annual Inspection: -
Generally boiler inspection is carried out annually but in case of any accident or abnormal complaint it should be done at any time. In this inspection all parts, mountings and accessories are removed and inspected.

The boiler is inspected from internally and externally for any defects which may develop during the course of its working. If the boiler found defect free then only the certification of registration is renewed.

03) Hydro Test: -
The hydraulic test is carried out to inspect the tightness of joints, fittings and the leakages from the repaired parts. To carry out this test, the boiler is completely filled with pressurized water. The water pressure is different for different situations as below,

01) For an old boiler, the hydraulic pressure applied will be 150% of the prescribed pressure for operation. At the given pressure the boiler should not leak at any spot.

02) For the new boiler,
A) The hydraulic pressure applied will be 200% of the working pressure and it should not leak under this pressure. The pressure mentioned is applied when the boiler has working pressure is less than 100 lbs/inch square.
B) When the boiler is working above 100 lbs/inch square, the hydraulic pressure applied for test is 150% + 50 lbs/inch square and the boiler should not leak at any spot under this pressure.

04) Steam Test:-
To check the setting of the safety valves at the working pressure, this test is carried out. After satisfactory test, the valves are sealed and the owner is not permitted to change the settings.

05) Inspection in Presence of Steam: -
This type of test is very rare but when boiler can not stop due to any reason, this test carried out. At the time of this test, steam generation is in process by boiler. A prior approval is from government is necessary to run the boiler after expiry date of its current certificate.

06) Internal Inspection: -
When boiler is small in size and when inspector can not enter inside for close inspection of internal parts this type of test is carried out. Inspection is done when internal parts are taken out for repairs.

07) Causal Inspection:-
To check out that the boiler owner is operating the boiler according to boiler act, the surprise visits from time to time are carried out for inspection.

08) Accident Inspection: -
If due to any reason accident took place, the boiler inspector holds an inquiry to fix the reasons of accident, the damage to the boiler and worker by inspection at site.

If you know something more on the topic, please add it by comments.

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Various Methods For Compounding of Steam Engines.

noreply@blogger.com (MechanicalGuru) — Fri, 19 Jun 2009 14:45:00 +0000

For greater efficiency and less space per horse power, high pressure steam is used in steam engine. Now with the use of this high pressure steam the range of expansion is correspondingly increased. If full expansion is takes place in single cylinder the walls of the cylinder to be made very thick to withstand the high pressure and also required a heavy flywheel. All this made a simple steam engine very heavy in construction, large variations of temperature and more leakage past the piston.

To overcome these difficulties, the expansion of steam is made in two or more cylinder. This called as “Compounding the expansion of steam”. There are three different methods of compounding of steam engines as below,

01) Tandem Compounding:-
In this type, the cylinders are arranged on common axis and two pistons have a common piston rod, connecting rod and crankshaft. The exhaust steam from high pressure cylinder passes directly into low pressure cylinder where it further expands.

The turning moment in this type of this type of engine is not uniform due to common crank and piston rod where all the torque acts at the same time. This is the basic disadvantage of such type of engines and requires a large flywheel. Tandem arrangement gives constructional economy because of less components of the engine.

02) Woolf Compounding:-
In this type, two cylinders are arranged side by side while the two cranks are placed at 180 degree to each other. The pistons of high pressure and low pressure cylinders begin and end their strokes together respectively.

The exhaust of steam from high pressure cylinder coincides with suction of steam in low pressure cylinder. In this case also exhaust steam from high pressure cylinder passes directly into low pressure cylinder where it further expands.

Since the two cranks are at 180 degree to each other, the two cycles are in phase and this causes large variation in the turning moment of crankshaft and necessitating the use of heavy flywheel.

03) Receiver Type Compounding:-
In this type, two cranks are mounted at 90 degree to each other that is why steam from high pressure cylinder can not exhaust directly into low pressure cylinder.

A container, known as receiver is used to collect steam from high pressure cylinder while low pressure cylinder draws steam from receiver for further expansion.

The turning moment in receiver type compounding steam is more uniform therefore a lighter flywheel can be used. With three cylinder engine, the cranks are arranged at 120 degree to each other but still small turning moment variation can be achieved.

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What Are The Advantages of Compound Steam Engine?

noreply@blogger.com (MechanicalGuru) — Thu, 18 Jun 2009 15:09:00 +0000

According to expansion of steam, the engines are classified as simple steam engine, compound or multi expansion steam engines, out of this; compound steam engines have more advantages than simple steam engine. The main advantages are as listed below,

01) Light weight cylinders are required in compound steam engine. The cylinder in simple steam engine is required to make strong and large enough to withstand the high pressure steam and to accommodate the large volume of low pressure steam respectively for the same expansion ratio comparing to compound steam engine.

Compound engines are light in weight as the high pressure cylinder only subjected to maximum pressure, but its diameter is small and low pressure cylinder is large in size but light in weight.

02) Temperature Range means the difference between the highest and lowest temperatures of steam within the cylinders and this range in each cylinder is reduced, with a corresponding reduction in initial cylinder condensation and temperature stresses.

03) In case of breakdown, the engine can be run on a reduced load by using only one cylinder. This feature gives great advantages especially in marine propulsion.

04) A lighter flywheel can be used in modern compound engines because of lower variation of turning moment as the cranks are at 90 degree to each other. This results in better mechanical balance, which allows higher speed of the engine.

05) After expansion in the high pressure cylinder the steam can be reheated before admission to the low pressure cylinder.

06) Because of the reduced pressure difference in each cylinder the leakage of steam past the pistons and valves are reduced.

07) There are less forces acting on the working parts as the forces are distributed over more components of the engine.

08) The compound steam engine may start in any position which is an advantage for locomotive and marine engines.

09) As there are two or more cylinders and pistons in compound steam engine the stroke length of each cylinder is comparatively less than simple steam engine.

10) For same horsepower the cost of the compound steam engine is less than simple steam engine because of lighter parts used in this type of engine.

You can add more advantages to above list by commenting.

How to Classify of Steam Engines in Different Way?

noreply@blogger.com (MechanicalGuru) — Wed, 17 Jun 2009 10:52:00 +0000

In old days reciprocating steam engines are used to convert heat energy into mechanical energy. Now a day’s steam turbine or internal combustion engines are used for the same work. But steam engine has many specialized applications. These steam engines can be classified according to its construction and operating features. Detail classification is covered as below.

A) Position of Cylinder: - According to the position of the cylinders steam engines can be classified as,
01) Vertical Engine
02) Horizontal Engine
03) Inclined Engine

B) Working Stroke: - Steam Engine is classified according to number of working strokes per revolution as,
01) Single Acting
02) Double Acting

In single acting engine there is only one stroke per revolution of the crankshaft as steam acts on one side of the piston. But in double acting engine two working stroke per revolution are obtained as steam acts on both sides of the piston.

C) Speed of Engine: - According to the running speed of the engine it can be classified as,
01) Low Speed Engine, Where engine runs at 100 or less revolution per minute.
02) Medium Speed Engine, Where engine runs at 110 to 200 revolutions per minute.
03) High Speed Engine, Where engine runs above 200 or more revolution per minute.

D) Field of Application: - Steam engines are classified according to its applications as,
01) Locomotive or Portable Engines
02) Stationary Engines
03) Marine Engines

E) Exhaust of Steam: - Steam engines are classified by exhaust of steam as,
01) Condensing Engines, Where exhaust steam passes into a condenser at lower pressure than atmosphere.
02) Non Condensing Engines, where exhaust steam passes directly to the atmosphere.

F) Governing Methods: - A classification is frequently made according to the governing method employed as,
01) Throttle Governing, in this method the speed of engine is controlled by means of valve in the steam pipe which regulates the pressure of the steam entering the engine.
02) Automatic Cut-Off Governing, in this method governor controls the quantity of steam admitted to the cylinder while the pressure of entering steam is remain constant.

G) Expansion of Steam: - Steam engines are classified according to expansion of steam in number of stages as,
01) Simple Steam Engine, where conversion of heat energy of steam into mechanical work in one stage only with one cylinder and piston.
02) Compound Steam Engine, where the conversion of heat energy of steam into mechanical work occurs in two stages with high pressure and low pressure cylinder.
03) Triple Expansion Steam Engine, where the steam expands successively in three cylinders.
04) Quadruple Expansion Steam Engine, where four cylinders and pistons are used for expansion of steam.

Besides above classification, steam engine can also be classified according its length of working stroke i.e. short stroke or long stroke engines and position of crank i.e. side crank or centre crank engines.

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What Are The Essential Qualities of Good Lubricant?

noreply@blogger.com (MechanicalGuru) — Fri, 12 Jun 2009 07:36:00 +0000

To reduce the frictional losses between metal to metal rubbing or sliding parts, lubrication is required. Below are the some essential qualities of a good lubricant.

01) Viscosity: - When any lubricant offered resistance to the deforming forces, it is called viscosity of the lubricant. Good quality lubrication oil must maintain sufficient viscosity at higher temperatures and it should not be too viscous at lower temperatures.

For high speeds, low viscosity lubricants are suggested while for large clearance and high loads; high viscosity lubrication oil is recommended. The viscosity of oil increases, if the temperature of mating surfaces decreases.

02) Flash & Fire Point: - Flash point of the lubrication oil is the minimum temperature at which it gives off enough vapour to form a momentary flash when naked flame is brought near its surface, while the fire point is the lowest temperature of the lubrication oil, where it burns continuously. To avoid the possibility of fire, the flash point of oil must be higher than the temperatures likely to be developed in the rubbing surfaces.

The fire point is generally higher than the flash point and the difference between flash point and fire point must be 18 degree centigrade at higher side.

03) Oiliness: - It is the property of lubrication oil to spread and attach itself firmly to the lubricating surfaces. When mating surfaces are subjected to a high intensity of pressure, it is recommended to particularly high oiliness; so that the metal is protected by a layer of oil and the wear is reduced.

04) Volatility: - Lubrication oil losses a certain weight due to evaporation when it is subjected to high temperature for long hours. This loss is known as “loss by evaporation”. The consumption of oil is considerably increased with high volatility at normal working temperatures that is why low volatility is always suggested for lubrication oil.

05) Stability & Insoluble Residue: - Stability of oil is to resist oxidation that would yield acids and sludge. Good lubrication oil must have high stability.

Free carbon or hydrocarbons decomposing into carbon at high temperature is called as insoluble residue. Good quality lubrication oil should not have any insoluble residue.

I hope the information above will help you to select proper lubricants for your machines.

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Tips about Suction and Discharge Valves Used In Reciprocating Air Compressor.

noreply@blogger.com (MechanicalGuru) — Mon, 11 May 2009 09:31:00 +0000

The performance of air compressor is mostly depending upon the condition of suction and discharge valves. These valves are very important part in any reciprocating air compressor and engineering field. That’s why due care must be required. Every valve requires a periodic inspection and maintenance. Here you will find, important information about suction and discharge valves used in Chicago Pneumatic Air Compressor.

01) Dismantling of valves:-
To avoid damage to the valve and inner dowel pins, it is suggested to use a simple fixture for dismantle and assemble valves. Never tightened the valve directly in a vice and do not hammer on spanner when loosening or tightening the nut.

02) Cleaning of valves:-
Examine all the parts thoroughly after dismantled the valve. Remove the carbon formation with the help of Trichloroethylene or diesel and light scraping paper or brush. Don’t scratch the valve plate or seat while cleaning. Completely dry out the valves before installing it on compressor.

03) Inspection and Reconditioning:-
When valve plate, damper plate, spring plate shows sign of wear, it is imperative to replace these parts, even if no breakage has occurred. A maximum wear of about 10 % of the total thickness of valve plate is allowed. For highest efficiency of the valve it is important that the seat face is flat and free from any traces of wear, thus preventing valve leakage. If any damage on the seat observed, it is recommended to replace the same. Dew to presence of dowel pins, re-machining or lapping can not be carried out. It is also suggested to use a new valve plate with new valve seat.

04) Reassembly and Installation:-

A) Do the valve assembly in required sequence. (Refer diagram from instruction manual) Use fixture for proper tightening of valve nut. Check valve plate for free movement.

B) Test valves for leakage and insure it made dry after testing.

C) Suction valve equipped with unloader, the clearance between the valve plate and unloader lifter as well as the clearance between unloading piston and lifter is checked.

D) Valve cover nuts have to be tightened with specific torque by torque wrench.

E) The hollow side of the thin part in the centre of the valve plate must be placed upward facing, valve keeper.

The above information will help you to increase life of suction and discharge valve and hence the discharge pressure of the air compressor.

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How To Start New Reciprocating Air Compressor.

noreply@blogger.com (MechanicalGuru) — Wed, 06 May 2009 07:45:00 +0000

Below points are most essentials in air compressor engineering.
01) Be certain leveling screw in frame base has been backed off, and foundation bolts are tightened properly.

02) Clean off all accumulated dirt from exterior of compressor and electric motor.

03) Remove covers, tapes, wrapping from openings, which had been blanked and sealed.

04) Open frame top cover and check all connecting rods, bolts etc. to see that they are correctly installed and tightened. Check crankshaft end float.

05) Check and clean thoroughly the inside of the frame. Use cloth for cleaning inside. Never use cotton waste on internal parts.

06) Remove silica gel bags if placed in valve ports, do not wipe any carbon and Teflon powder from valve or cylinder. (For Non Lubricated Compressor.)

07) Fill compressor frame with correct grade of oil up to required level. (Middle of the visual screw)

08) Rotate the compressor manually, in direction of rotation and check bearing lubrication as well as free running of crankshaft.

09) Fill oil in force feed lubricator, disconnect oil line near to cylinder and rotate handle. Check oil is coming at the end of lubricating pipe. Reconnect oil line and operate pump at least 20-25 turns.

10) Check each compressor piston rod to be certain it is smooth and rust free, especially for the section where rod is passing through packing and wiper rings.

11) Check the bumping clearance as per recommended.

12) Replace frame inspection cover on the compressor.

13) Check compressor air cleaner and suction lines for dirt and clean, if required.

14) Check all electrical connections for correct tightness.

15) Check the insulation resistance with megger. If any moisture or dirt in the winding indicated, remove it immediately.

16) Remove safety devices and start motor without v-belts. Check the incoming voltage and current drawn by motor. Check electric motor for abnormal noise and vibrations.

17) When satisfied with electric motor, fit v-belts, align motor and adjust belts tension as required.

18) Check strainer/air filter before unloader and insure pressure sensing airline is clean and free from rust, dust etc.

19) Remove all suction and discharge valves and starts motor. Check oil pressure unusual noise, vibration and safety trappings.

20) Shut down compressor, check all parts for unusual heating. Install all suction and discharge valves.

21) Restart compressor and continue to run until the unit has warmed. Check various temperature and pressure gauges for proper operations.

22) If found every thing in order, put the compressor air discharge net to supply compressed air for plant utilities.

Follow all the above instructions while commissioning every new or overhauled reciprocating air compressor.

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Different Combustion Chambers Provided In Diesel Engines.

noreply@blogger.com (MechanicalGuru) — Tue, 05 May 2009 09:50:00 +0000

When we are going to design the combustion chamber of diesel engines the main consideration we have to keep in mind is, high compression ratio & sufficient turbulence of air. For high compression ratios overhead valve s are more preferred than side valves. Below are the some shapes of combustion chambers discussed.

01) Open or Direct Injection Chamber

For moderate & low speed engines this type of combustion chamber is most suitable. The fuel is injected directly in the combustion chamber, which is formed by a part of the piston, where it penetrates the mass of hot compressed air. The injector pressure is more than 21 kilogram per centimeter square is used. The fuel injector is placed in the center of the chamber and contains more than four orifices. Due to location of orifices the spray pattern suits the combustion chamber & does not impinge on the wall of the cylinder or piston.

This design is used by Leyland Motors Ltd has the chamber in the form of a truncated cone and the fuel injector is located near the circumference of the chamber. In some engines two injectors are located on the opposite side of the chamber. The open type of combustion chamber depends upon the primary turbulence as the main source of air movement due to which engine can start in cold condition and don't required heater plug.

02) Auxiliary Combustion Chamber

In small high-speed engines, this type of combustion chamber is mostly used. Total fuel is directly fed into an auxiliary combustion chamber where the initial combustion takes place. Due to rise in pressure the partially burnt mixture is forced at high velocity through a small orifice into the main combustion chamber where the rest of the combustion aided by secondary turbulence takes place.

As the piston descends during power stroke, the pressure difference created between the precombustion chamber and the main chamber assists in discharging the hot exhaust gases from the precombustion chamber. This type of combustion chamber has very low maintenance cost due to low injection pressure and simpler single nozzle orifice. The main combustion chamber is subjected to less pressure since the pressure shock is mainly taken by precombustion chamber. This type of combustion chamber gives clean exhaust but heat losses are higher due large surface area of two chambers.

03) Air Cell

In some designs small chamber is provided which is called as air cell. They are away from the fuel spray nozzle, which is so located that the fuel is sprayed near the narrow neck, which connects the air cell with the main combustion chamber. Piston compresses the air during compression stroke and pushes it into air cell. As the piston moves down the pressure in the cylinder falls resulting in the flow of hot air from the cell into the combustion chamber producing the secondary turbulence, which mixes the air & fuel further and completes the combustion. The air cell also requires a high compression ratio and heater plugs for starting. The heat losses are more due to large wall area.

04) Ricardo Comet Chamber

This combustion chamber is separated from the cylinder and one of the most efficient combustion chamber. In this type chamber air enters in tangential direction during compression stroke and imparts a rotary motion. The fuel is then injected into the hot compressed air and the combustion takes place. Reversal of flow takes place due to pressure rise and the hot gases are discharged into the cylinder pushing the piston up ward in working stroke. Due to higher temperature of air in the combustion chamber, fuel of low ignition quality can also be burnt satisfactorily.

05) Energy Cell

It is also called as Lanoxa chamber and works on combined principles of air cell & auxiliary combustion chamber. As fuel injector sprays the fuel, 10% of fuel passes across the combustion chamber & enters in energy cell. The combustion generally starts in the main chamber, spread to the energy cell where pressure rise considerably. Due to pressure difference between the energy cell & main combustion chamber, the hot gases from the minor cell, will sweep the fuel from the minor cell, into the combustion chamber where additional turbulence is set up to ensure complete combustion of fuel.

A restricted opening can be closed by plunger, which connects major cell with the minor cell, this effects smooth starting. Once the engine is started the restricted opening can be opened out so that the minor cell is connected with the major cell. Through a small opening, minor cell communicates with combustion chamber. Due to this small opening the hot gases are throttled and so the pressure rise in main combustion chamber is gradual. Since the fuel is sprayed direct in to the main combustion chamber where the air has highest temperature resulting in complete combustion.

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Governing Methods Of Internal Combustion Engines.

noreply@blogger.com (MechanicalGuru) — Wed, 18 Feb 2009 10:56:00 +0000

The term "Governing" means the action of varying the fuel supply in accordance with the load demand so that the engine runs at practically constant speed. Below are the some important methods of governing of internal combustion engines.

01) Hit & Miss Governing-
This method is suitable for small gas engines. In this, the rotational motion of the cam actuates the rocker through the roller. The rocker carries a pecker, which strikes against the pecker block and lifts the valve against the pressure of the spring. At very high speed, the pecker block is lifted by the rod due to rise up of governor sleeve resulting the engine performs an idle cycle because no fuel is now being supplied.

This method of governing is quite simple but owing to the violent explosions which usually occurs as a result of extra scavenging which takes place immediately after "missed explosion', produces uneven turning moment necessitating the use of heavy flywheel which increase the friction at the bearing and lowers the mechanical efficiency of the engines.

02) Qualitative Governing-
This method is widely used in all heavy oil engines besides being always used on two stroke cycle engines in which the air fuel mixture has to be admitted to the engine cylinder to drive out the burnt charge of the previous cycle.

In this method, under the action of centrifugal governor the amount of fuel entering the cylinder is varied by altering the stroke of the Oil Pump or by passing a part of fuel which would have otherwise been injected into the engine cylinder back to the oil tank or by delaying the closing of the suction valve in the fuel pump.

03) Quantitative Governing-
In this method, the quantity of air -fuel mixture flowing into the cylinder is varied accordingly. This may be done by decreasing the lift of the inlet valve or by throttling the mixture before it is made to enter the engine cylinder. This method is largely used for governing petrol and big gas engines.

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How To Prevent Diesel Knock In Internal Combustion Engine?

noreply@blogger.com (MechanicalGuru) — Sat, 14 Feb 2009 11:13:00 +0000

When sudden and violent knock are experienced in petrol engine, these knocks are termed as "Detonation". Just like petrol engines, a high-pressure wave set up in compression ignition engine (Diesel Engine) and this wave strikes the cylinder wall, cylinder head and piston resulting in knock. These knocks are known as "Diesel Knock".

There is power and efficiency loss along with rough running of engine is observed due to diesel knock. In severe cases it may wreck the engine.

A considerable amount of air -fuel mixture may ignite at the same instant and result in a combustion knock or heavy thud rather than pink. While it is end mixture which knocks in the spark ignition engine (petrol engine) it may fairly large part or parts of the mixture, which knock in compression ignition engine.

To prevent diesel knock, following important methods can be used very effectively.

01) Add 1% of ethyl nitrate or any nitrate to accelerate the combustion of fuel. This process in known as "Doping" and reduce delay period considerably and hence prevent diesel knock.

02) For spontaneous ignition of the fuel, we require much higher temperature this can be achieved by raising the compression ratio. The rate of pressure rise increases resulting in smooth running of the engine. If compression ratio increased in petrol engine, the engine is more liable to detonate, but in diesel engine it reduce the diesel knock.

03) Diesel knock can be reduce by increasing the turbulence of the compressed air injected promotes homogeneous mixture by stripping the fuel from the spray.

04) Arrange the fuel injector in such a way that it should start injecting only a small quantity of fuel in starting of the engine. If we increase the injection pressure, which encourages the atomization of fuel and prevent knock.

05) By raising the temperature of the coolant that of the intake air as well as cylinder head and combustion chamber.

06) By increasing the inlet pressure of air (Supercharging) we can prevent diesel knock.

Many times we noted this sudden noise but not aware about the phenomenon behind this, now above description will clear the doubt about knock in your automotive engine. What you say?

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10 Important Terms Used In Internal Combustion Engine.

noreply@blogger.com (MechanicalGuru) — Fri, 13 Feb 2009 08:57:00 +0000

For the better knowledge of internal combustion engine every one must know about the following terms,

01) Carburetion: -
The process of breaking up the fuel into minute particles and mixing it with air is called "Carburetion". This process is mostly used in the internal combustion engine, which have low compression ratio and which use highly volatile liquid fuels such as petrol. The process of breaking up fuel in minute particles is known as "Atomization". Carburettor is the device where all the carburetion takes place.

02) Scavenging: -
The process of removing burnt exhaust gases from the combustion chamber of the engine cylinder is known as "Scavenging". In four-stroke cycle engine, the piston pushes the burnt gases to exhaust manifold during its exhaust stroke. In the two-stroke cycle engine a blast of fresh charge is made to enter at higher Velocity into a combustion chamber at the end of working stroke and thus drives out burnt exhaust gases.

03) Compensation: -
The process of providing additional fuel or reducing the fuel by certain means to correct the mixture strength to meet the varying nature of speeds and load on the engines is known as "Compensation". This process is mostly used in simple carburettor specially used for automotive purposes.

04) Firing Order: -
The sequences in which firing or power impulses occur in an internal combustion engine are called "Firing Order". The firing order should be such that there is always a proper balance and it does not cause vibrations.

05) Detonation: -
Some sudden and violent knocks are experienced in internal combustion engine at sometimes. This knocks are known by "Detonation". This knock is set up by a high-pressure wave giving a loud pulsating noise as it strikes against the cylinder walls, cylinder head and piston. It should be noted that detonation is not pre-ignition but something, which occur after the spark, has started the ignition.

06) Doping: -
The process of adding small quantity of Tetraethyl lead to suppress the detonation in petrol engine is called "Doping". If the tetraethyl lead used in large proportion, there are chances of engine damage due to deposition of lead oxide in the combustion chamber.

07) Diesel Knock: -
A high-pressure wave set up in compression ignition engine (Diesel Engine), which causes knocks. This knock is called as "Diesel knock". It badly affects the engine efficiency and power drop; also engine runs very rough due to diesel knock.

08) Dissociation: -
If a gas or mixture of gases is heated to very high temperature, the vibrating molecules of different gases make violent encounters resulting in splitting up of the compound molecules into smaller molecules which recombine to form their compound molecules as the temperature lowered. The phenomenon is called "Dissociation". The dissociation is mainly due to breaking up of carbon dioxide into carbon monoxide and oxygen.

09) Supercharging: -
The process of increasing the weight or density of air-fuel mixture or compressed air, induced into the cylinder during the induction stroke is known as "Supercharging". This is achieved by a separate compressor and known as supercharger or blower.

10) Turbulence: -
When the atomised fuel injected into the combustion chamber of compression ignition engine may be burnt efficiently there should be a high relative velocity between the air and fuel so that a thorough mixing takes place. This is achieved by "Turbulence".

I hope this will help you to get better knowledge about your engine and can increase the performance of engine.

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How To Cool Exhaust Valve Of Internal Combustion Engine?

noreply@blogger.com (MechanicalGuru) — Thu, 12 Feb 2009 13:55:00 +0000

Various strokes are performed in internal combustion engine to get work done up to our requirement. To complete suction and exhaust stroke, there are some valves used which are known as suction valve and exhaust valve. Suction valve allow the fresh charge of air-fuel mixture inside the cylinder, where it is compressed and burnt by other parts. Due to combustion process large heat is developed and it makes exhaust valve very hot as burnt gases are escape from this valve to atmosphere.

As exhaust valve of an internal combustion engine is subjected to very high temperatures, it is therefore necessary to cool it down for the better performance of engine. Following ways can cool exhaust valve in,

01) By providing a suitable number of jets on the channel through which cold water directs from the radiator are pumped. The water flowing from these jets or nozzles in contact with the areas adjacent to the exhaust valve and exhaust port, which are thus cooled.

02) An improved Cooling can also be achieved if cooling jackets are provided more elaborately near exhaust valve and exhaust port.

03) By filling a part of the stem of the exhaust valve by sodium, we can achieve better Cooling. The solid melts at high temperature (Near about 750 degree centigrade) and is thrown up and down due to the motion of the exhaust valve. The heat from the hot region is thus conveyed to the comparatively cold region. Sodium is good conductor of heat and has a high boiling point. (750 degree centigrade)

It is more important to keep all the parts in workable limits for the better efficiency of the internal combustion engine. As a mechanical engineer, we have to take care of all our various machines and components.

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Factors Affecting Detonation In Internal Combustion Engine.

noreply@blogger.com (MechanicalGuru) — Sun, 08 Feb 2009 10:15:00 +0000

In an internal combustion engine cylinder sometime sudden and violent knocks are experienced, this is known as "Detonation". This knock is set up by a high pressure wave giving loud pulsating noise as it strikes against cylinder walls, cylinder head and piston.

A mild detonation will simply heat the engine but if the detonation is severe, it may even result in fracture of the piston or other damages to the engine.Detonation also results in increased carbon deposits. If detonation continue for a long time it may overheat the cylinder and spark plug so as to ignite the Charge even before sparking and lead to pre-ignition. These are the disadvantages of detonation. A properly designed combustion chamber will reduce detonation considerably.

Following are the main factors, which affects detonation,

01) The fuel used in internal combustion engine will considerably effects on the chances of detonation. Alcohol and benzol do not cause detonation but it can not be use due its low calorific value and other objections to use as fuel. Again alcohol cannot blend with petrol in the presence of water.

02) The detonation is also promoted by increase in compression ratio. The compression ratio at which detonation just occurs is known as the Highest Useful Compression Ratio. Higher the compression ratio higher the chances of detonation and lower the output.

03) If the carbon deposits are in the cylinder and used excessive sparking temperature, the detonation will increased rapidly.

04) The position of the spark plug in a combustion chamber determines the distance the flame has to travel in order to reach the detonation zone. More the distance more the chances of detonation. A centrally placed spark plug works better. Spark plug must be placed near to exhaust valve but the exhaust must be located away from detonating zone.

05) Higher temperature of the walls of combustion chamber tends to raise the temperature combustion chamber tending to raise the temperature of Detonation zone.

06) The rate at which the combustion of the portion of the fuel, which is first to ignite immediately after the application of the spark, also affects detonation.

Hence from the above description we must know, the detonation is dangerous for internal combustion engine and must be removed or reduced.

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Various Parts Of Water Cooling System.

noreply@blogger.com (MechanicalGuru) — Sat, 07 Feb 2009 09:45:00 +0000

Internal combustion Engine can be cooled by air-cooling or water-cooling method. Various Water Cooling Methods Of I.C.Engine is covered in earlier post, which you can refer to know in details. Impeller Thermosyphon system has required following components to perform the cooling action.

01) Radiator:-
The function of the radiator is to cool down the hot water from engine. It consists of a large number of vertical tubes through which water flows down. The temperature of water is reduced appreciably by drawing the air through spaces between the radiator tubes with the help of fan, which is mounted on the impeller spindle driven by a suitable pulley arrangement.

There are many types of radiator tubes are used in field but the most common is tubular type. It consists of a large number of circular brass tubes pressed into a number of suitable punched parallel brass fins. The tubes are tinned to guard against corrosion and are staggered. The main disadvantage of this design is, a greater inconvenience to repair any damaged tubes. Still it is cheaper than the honeycomb type design due its initial cost. The honeycomb radiator is used in racing cars.

The water used for cooling must be soft because the deposits given out by hard water act as insulator of heat between the cylinder walls and the radiator water, but in case where soft water is not available, 0.03 kilogram of sodium bichromate should be added for every 13 kilogram of water.

The maximum temperature, which can be allowed in a radiator, is 3 degree centigrade below boiling point of water. The ratio of the observed temperature difference to the greatest permissible temperature difference in a radiator is called suitability of of the radiator.

Some radiators are equipped with a heater, which not only averts the danger of freezing of water but also greatly reduces the time taken by the engine to reach its normal operating temperature.

02) Fan and Pump:-
The pump increases the velocity of water through the system. The fan, which draws air through the radiator spaces, is usually mounted on the same spindle as that of the impeller having widely spaced vanes to facilitate the flow of water through it is case of failure.

The bottom of the radiator is connected to the suction side of the pump. The power is transmitted to the pump spindle from a pulley mounted on the end of the camshaft or crankshaft.

03) Thermostat:-
A thermostat fitted in such a manner that it prevents the flow of water below certain temperature, from engine to the radiator. The "Bellows Type" thermostat is generally used.

The disc is connected to the bronze bellow through link. The bellows are sealed against the atmosphere and contain alcohol inside it. On cooling, the bellows contract due to the condensation of alcohol vapour into liquid. The disc therefore closes the passage, which could be reopened only if a certain minimum temperature of the circulating water is reached which expands the bellow due to evaporation of the alcohol liquid inside. Generally, a thermostat does not allow the water to flow below 70 degree centigrade.

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Various Water Cooling Methods Of I.C.Engine

noreply@blogger.com (MechanicalGuru) — Wed, 04 Feb 2009 11:47:00 +0000

To pass some of the heat generated due to combustion in the cylinder of internal combustion engine, air-cooling or water-cooling methods are used. The Details about air-cooling were covered in previous post (Air Cooling Of Internal Combustion Engine.). In this post you will find some more methods of water-cooling.

In water-cooling method, the advantage of superior convective and conductive properties of water is used. Water is circulated continuously through the Cylinder with an annular space known as Water Jacket. To avoid unequal expansion in the cylinder bore and burning of lubricating oil, the water jackets are so designed that they will cover the entire length of piston stroke.

For the cleaning of water jackets in large cylinders, cleaning doors are provided. This method is also employed in large reciprocating air compressor where we have to add cooling tower in addition to cool the circulating water.

Water Cooling can be done by any of the following methods,

01) Direct Method:-
In this method, water from a storage tank is directly supplied through an inlet valve to the engine cylinder. The hot water is simply discharged and not cooled for reuse. It is suitable for large industrial units and where plenty of water is easily available.

02) Thermosyphon Method:-
In this method, hot water from engine cylinder flows towards radiator, which has comparatively cold water, and get cool down.

In order to ensure that the coolest water is always made available to the water jackets the latter should be located at as low a level as possible with respect To the radiator.

This system is useful due its simplicity and automatic operation, but there is disadvantage of water freezing in cold weather condition. We have to use large Quantity of water, as there is slow rate of circulation observed.

03) Impeller Thermosyphon Method:-
Here the flow of water takes place by convection assisted by a pump. The latter is made non-positive type, which even when stationary; allows the flow of water to take place. Thus when the working of pump fails water can still circulate on the thermosyphon system.

In its simplest form, water flow from radiator to engine and back to radiator. A thermostat is employed in system, which prevents the flow of water below a certain temperature, from the engine to the radiator. This we have to do to acquire some of the temperature at starting of the engine.

This system has three major parts, (The details about this parts will be covered in coming post.)

01) Radiator
02) Fan and Pump
03) Thermostat

04) Full Pump Circulation Method:-
In this method, a positive supply of water by a centrifugal pump placed in the system. This system works on higher Velocity of circulating water due to which less quantity of water is required hence we can use smaller radiator.

In some designs the piston is cooled by oil squirted against the piston crown underside through a nozzle located in the connecting rod small end.

05) Evaporative Cooling Method:-
In this method, the engine may be cooled by evaporating the water in the cylinder jackets, into the steam, which absorbs Large quantity of heat and raise to the top of the engine from where it flows into a tank at the bottom of the radiator and then flows upwards and gets Condensed before reaching the top.

Due to large quantity of latent heat absorbed during evaporation of water into steam the weight of the circulating water is only 40% of that in other water Cooling methods. Hence smaller radiator can be employed.

This system is quite useful where plenty of water is not available. The higher running temperature no doubt reduces the friction in the piston but the volumetric efficiency is reduced and the engine is also liable to detonate.

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Air Cooling Of Internal Combustion Engine.

noreply@blogger.com (MechanicalGuru) — Tue, 03 Feb 2009 10:07:00 +0000

When the combustion of fuel takes place in cylinder of internal combustion engine, a very high temperature is developed. It is, therefore necessary to extract some of the heat from cylinder to atmosphere. It will avoid damage to the cylinder and piston. Heat also burns lubrication oil and form carbon. There is possibility of seizure of piston inside the cylinder, which will lead to more break down and repairing cost. To avoid this, cooling is necessary.

Air Cooling is mostly used in motorcycles, scooters where the forward motion of the machine gives a good velocity of air to cool the engine. Air Cooling is also provided in small industrial engines. In bigger unit a circulating fan is employed. But the fan absorbs 5% of the power developed by the engine.

Air Cooling is the simplest method in which the heat is carried out by the air flowing over and around the engine cylinder. In this system a current of air is Made to blow past the outside of cylinder barrel whose outer surface is area has been considerably increased by providing radiating fins. The cooling fins are arranged so that they are perpendicular to the axis of the cylinder.

In this system there is no such problem as corrosion or clogging of the radiator occurs, since there is no radiator is used (Radiator is used in water cooled Engines). There is also a complete absence of water freezing in cold weather conditions as in water-cooled engine.

Air Cooling is particularly advantageous where there are extreme climatic conditions as arctic or where there is lack of water as in deserts. It gives less Starting troubles.

Beside above advantages, this cooling system has some disadvantages also. Air-cooled engines on the average have limited size, non-uniform cooling and Higher working temperatures. They also produce more noise, gives a less petrol economy, lower maximum allowable compression ratio and lower output.

In next post, you will come to know about water-cooling of internal combustion engine.

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Common Defects In Water Cooling System And Its Rectifications.

noreply@blogger.com (MechanicalGuru) — Sun, 01 Feb 2009 10:06:00 +0000

The heat is generated in engine due to combustion of air-fuel mixture that is why the Necessity Of Cooling In Internal Combustion Engine is required.This is done by air or water.Each cooling system has its own advantages and disadvantages,the most common defects occurring in water cooling system are,

01) Loss Of Coolant:-
Water leakage and water evaporation is the main cause of water loss from the cooling system.Water leakage may occur due to faulty head gasket,loose cylinder head,cracked head or engine block,loosening of hose clamps and radiator pipe leaks.

To stop such a leakage,head gasket may be replaced,hose clamp may be tightened and radiator pipe soldered.To compensate the loss of water due to evaporation can be done by filling the water at correct level in radiator.
02) Overheating Of Coolant:-
This is caused due to rusting,sealing of water jackets and radiator, defective hose,defective water pump,defective thermostat,slipping of fan belt,blocking of air passage in the radiator and loss of cooling water.

The heat transfer from the wall of the cylinder to the coolant is mostly effected due to rusting and scaling takes place on the walls.This may be removed by washing the cavities with ordinary washing soda or some other chemical and reverse flushing.

Sometimes worn out hose material goes into the water passage and accumulates there restricting the flow of coolant.Replace the defective hose at earliest.Repair defective water pump and replace defective thermostat Will solve the problem.The circulation of air is effected by slipping of fan belt.To remove this defect,tightened the fan belt as per requirement or replace if required.Remove the greasy material if found on pulley grooves.

Clean the radiator by blowing air under pressure from fan side.If there is loss of coolant due to any reason,the water must be filled in radiator up to required level without hesitation.

03) Over cooling Of Coolant:-
Over Cooling is generally caused by a thermostat that opens too early or remain open at all times.In some cases,it is observed that there is no thermostat employed or missing.If By-Pass valve remain open at all time,it results the over cooling of water.to avoid over cooling,the defective thermostat must be replaced and early action should be taken to close the By-Pass valve.

The circulation of water may be effected due to freezing of cooling water as it blocks the circulation passage.To overcome this problem,the engine must be run idle for some time until it attains the proper temperature.

04) Water Circulating Pump Noise:-
Water pump gives noise due to dry bearing or bushing,loose pulley on the pump shaft,loose impeller on the shaft etc.The proper cause of trouble may be found out and rectified.

05) Defective Temperature Gauge:-
If the temperature gauge on the panel is suspected to be giving incorrect readings the temperature of the cooling water be measured by inserting a thermometer in the radiator upper tank and then compared with the reading of the gauge.If the gauge is found defective it should be replaced.

There are may be some more defects which you know better than me,add it by comment.

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Necessity Of Cooling In Internal Combustion Engine.

noreply@blogger.com (MechanicalGuru) — Fri, 30 Jan 2009 10:38:00 +0000

To get the work done from internal combustion engine,we have to burn air-fuel mixture inside the cylinder.When the combustion of air-fuel mixture takes place in the engine cylinder,a temperature as high as 2500 degree centigrade is reached.To withstand such a high temperature we have to use very high melting point material for construction of engine.Practically it is less possible because,"Platinum" a metal which has one of the highest melting point,melts at above 1800 degree centigrade.

It has been practically found that out of total heat generated by internal combustion engine due to combustion of fuel,only 30% of heat is converted in useful work,out of remaining 70% about 40 % is carried by exhaust gases into the atmosphere during exhaust stroke.The rest of 30% must be passed to atmosphere by some suitable arrangement.

Here we find the necessity of cooling.In addition to overheating,large temperature differences may lead to distortion of the engine components due to set up of thermal stresses.If the cooling system is not provided to internal combustion engine,the lubricating oil film would break down and the lubricating oil will decompose to give gummy and carbon deposits.
In lack of Cooling system,a complete seizure of the piston,bearing and other important parts will occur.Due to this,there will be more frequent replacement of the components are required.It will also increase the repairing cost and breakdown period.The engine life will be reduced considerably.

It should also be noted that higher temperatures lower the volumetric efficiency of the engine,promote pre-ignition and tendency of the engine to detonate.The object of cooling is achieved by any of the two methods,
01)Air Cooling
02)Water Cooling

Properties of an efficient cooling system:-

The following are the two main properties desired of an efficient cooling system,
01)It must be capable of removing only about 30% of the heat generated in the combustion chamber.Too much heat removal will lower the thermal efficiency of the engine.
02)It should remove heat at a fast rate when engine is hot.It is also required to be very slow cooling at the starting of the engine,so that the different working parts of the internal combustion engine reach their operating temperature in a short time period.

If you are using Water cooled engine,then are little chances of freezing of water in cold weather conditions,if we keep engine without use for very long time. To overcome this problem,we have to mix anti freezers in cooling water.

The different cooling systems employed in various automobile will be covered in next post.

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noreply@blogger.com (MechanicalGuru) — Thu, 29 Jan 2009 08:54:00 +0000

To ignite the mixture of air-petrol inside the cylinder,a spark plug is used.A spark plug which is screwed into the cylinder head is usually designed to withstand a pressure about 35 kilogram per centimeter square and operate under 10000 to 30000 volts.

Construction Of Spark Plug:-

The core insulating assembly is housed in the steel shell assembly.The lower threaded portion of the shell which has 18 millimeter or 14 millimetre diameter thread on standard plugs has ground electrode welded to it.The centre electrode is screwed into the insulator at its upper position.The upper end of the centre electrode is connected to the terminal which communicates with the distributor.

When high voltage is applied,the spark jumps in the small gap which is provided between the lower end of the centre electrode and the ground electrode.This spark is responsible for starting ignition in the cylinder.

Platinum,nickel are generally used as electrode material due its capacity to withstand corrosives,high temperature and has good thermal conductivity.The insulator should have a good thermal conductivity,chemical inertness to gases of combustion,high resistance,be non-brittle and able to withstand high temperature and pressure.In recent practice is to use aluminium and silicon oxides also.

In order to prevent the escaping of gases from the cylinder to the atmosphere, suitable sealing gaskets are provided between the shell and the core insulator.Another steel gasket is also provided at the area where the steel shell is to contact cylinder head when the spark plug is screwed in its proper position.The leakage of the hot gases past a defective or worn out gasket is likely to raise the temperature of the plug.

Generally 0.3 to 0.6 millimeter gap is kept in the spark plug.Under special circumstances a 0.7 millimeter gap can also be kept.The efficiency of the entire ignition system is greatly reduced both by too large or too small gap.Therefore,the gap must be kept in the desired limits.

The deposit of foreign materials such as carbon between the electrodes or on the outside of the insulator between the plug terminal and the shell are source of nuisance and permit some of the high voltage to by-pass gap resulting in a reduced intensity of spark giving decreased engine efficiency.To avoid carbon deposits,we should have to operate spark plug above 400 degree centigrade.By bending the ground electrode,we can adjust the gap of plug.

There are two types of spark plugs used for automotive purpose,

01) Hot Plug:-
In this spark plug,the path traced by the heat received by the plug,to reach the Cooling cylinder head water is longer so that the plug can be maintained at a high temperature to burn carbon deposits.

02) Cold Plug:-
It has a shorter insulating nose which increase the rate of heat transfer due to short conducting path.This type of spark plugs are suitable for the engines,running a high speed and having high compression ratio.

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noreply@blogger.com (MechanicalGuru) — Thu, 29 Jan 2009 05:00:00 +0000

All Petrol Engine used electric spark ignition.The compressed air-petrol mixture in a petrol engine must be fired at the correct instant so that the resulting rise in pressure acts on the piston when it is at top dead centre.A high voltage is required to jump the gap of a spark plug and give a spark of sufficient energy to ignite the mixture.

As the speed of a spark ignition engine increases,it is desirable that the spark advance increase as the ignition time stays constant but the cycle is completed in less time.Some devices are employed for this purpose.The details about such mechanism is as below,

01) Centrifugal Advance Mechanism:-
In this mechanism,the drive shaft is connected to the ignition cam through base plate,spring loaded weight and an advance cam.The latter integral with the ignition cam.When the speed of the engine increases,the centrifugal force pull the weights out against the spring force thus advancing the angular position of the cam relative to drive shaft.

This action opens the contact points earlier and the ignition timing is therefore advanced.With decrease in the speed the springs pulls the weight inwards and bring back the cam thus reducing the spark in advance.

02) Vacuum Advance Mechanism:-
In this case,flexible diaphragm is kept in the fully retarded position by the force of a spring.One face of diaphragm is exposed to the atmosphere through the air vent,the other face is exposed to vacuum in the sealed vacuum chamber which is connected by a pipe line to the induction manifold.

The part loads due to vacuum the diaphragm is pushed upwards by the air pressure and the angular position of the cam in the distributor is advanced through the actuating rod,so that the spark now occurs earlier.When the engine runs on full load,the suction in the manifold decreases and the diaphragm is pushed downwards by the spring thereby retarding the cam.

This way we can increase the timing of spark ignition in our petrol engine.
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noreply@blogger.com (MechanicalGuru) — Wed, 28 Jan 2009 08:59:00 +0000

For the combustion of fresh charge of mixture it must be burn in cylinder.This is done with the help of spark plug.A spark is produced in spark plug by ignition system.The details about various ignition system will be covered in this post.

01) Coil Ignition System:-

This ignition system consists of a 6 or 12 volt battery,resistance,ignition switch,ammeter,high tension coil,contact breaker,condenser,high tension distributor and spark plug.

The high tension coil consists of a Water proof casing containing a few turns of heavy wire forming a primary winding surrounded by about 20000 turns of fine wire forming secondary winding,both the windings being wound over a laminated soft iron core and insulated from each other.One end of secondary winding is earthed while the other end connected through a heavily insulated wire into the centre of the distributor cap.

A carbon contact carries the current to the rotor arm,made of bronze which revolves and distributes the current to the various cylinders through spark plug leads.Thus the rotor arm connects the proper spark plug to the secondary winding at the required moment.

As the flow of current through the primary winding is stopped by the contact breaker,a very high voltage( near about 8000 to 10000 volts) is induced in the secondary winding.This voltage is supplied through the high tension distributor to the appropriate spark plug gap there by producing a spark.The high tension distributor and the contact breaker,are placed in one body.

The condenser in the primary circuit prevents sparking at the contact breaker points.It also increase the electromotive force in the secondary at break while it further decrease the electromotive force in the secondary at make thus giving a high voltage unidirectional current.

The contact breaker consists of a cam with a number of lobes on it,a fixed post holding one contact while other contacts is mounted on a movable arm.The material used for contacts are platinum and tungsten.

The contact breaker points are opened only 3 to 3.5 millimeter apart.The high tension distributor is prevents the serious trouble that are likely to be developed in the high tension coil either when the current flows due to a faulty circuit or when the ignition switch is left in the "On" position,in either case the high tension coil may be heated up giving an inferior performance.

The resistance wire may also act as a fuse breaking the primary circuit thereby avoiding the discharge of the battery.

02) Magneto Ignition System:-

This system consists of a switch,a magneto,contact breaker,condenser,high tension distributor and spark plugs.

The magneto consists of a fixed armature having primary and secondary winding and a rotating magnetic assembly driven from the engine.
The electromotive force induced in the secondary is insufficient to produce a spark.Consequently it is transformed into the high voltage by the contact breaker in the primary circuit.The voltage induced may be more than 10000 volts.

The spark is produced at the correct moment in the proper cylinder with the help of high tension distributor.(As per the action takes place in coil ignition system.)

I hope,this will give you a little knowledge about ignition of your vehicle.what you say?

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noreply@blogger.com (MechanicalGuru) — Sat, 24 Jan 2009 09:13:00 +0000

It is most important to perform the engine as per our requirement.The performance of engine depends on mean effective pressure and rotational speed.Since mean effective pressure is limited by fuel and strength of materials,the only way to have higher performance is to have higher rotational speed.

In high performance engines it is usual to open the valves earlier and close them later so that the opening time is more thus ensuring the maximum amount of fresh mixture at higher rotational engine speed and greatest possible clearance of exhaust gases.

In some unsupercharged racing cars inlet valve opens as early as 25 degree before top dead centre and closes 60 degree after bottom dead centre.Exhaust valve opens 55 before bottom dead centre and closes 25 degree after top dead centre.

Thus we see that the inlet and exhaust valves open and close in four stroke Otto cycle engine as follows,

01) Inlet valve opens 10 to 30 degree in advance of top dead centre position.Closes 30 to 60 degree after bottom dead centre.

02) Exhaust valve opens 30 to 60 degree in advance of the bottom dead centre position.Closes 8 to 25 degree after the top dead centre position.

It has been found practically that the actual maximum pressure in such engine is only about half of the theoretical value,because the inlet and outlet valves do not open and close suddenly but take some time to operate.

Because of the resistance of the inlet valve of the entering charge,the actual pressure inside the cylinder during the suction stroke is slightly less than atmospheric pressure.Similarly because of the resistance of exhaust valve to exhaust gases leaving the cylinder,the actual pressure inside the cylinder during exhaust stroke is slightly higher than atmospheric pressure.

Due to this there are some losses occur which is called as "Pumping Loss".This loss is treated as negative and therefore subtracted from the positive work done,thus we get net work done during the cycle.

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