IC engine

Lower Heat Value of Fuel:

The lower heating value (also known as net calorific value) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25°C) and returning the temperature of the combustion products to 150°C, which assumes the latent heat of vaporization of water in the reaction products is not recovered.

High Heat Value of Fuel:

The higher heating value (also known gross calorific value or gross energy) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25°C) once it is combusted and the products have returned to a temperature of 25°C, which takes into account the latent heat of vaporization of water in the combustion products.

Unit of Heat Value:

Btu = British thermal units; scf = standard cubic feet

Cut-off Ratio:

·         The cutoff ratio is the ratio of the volume after combustion to the volume before combustion.

·         The Air standard efficiency of a diesel cycle is given as:

η=1−1/(R^(γ−1))*[γc^(γ−1)/γ(γc−1)]

·         where,

RoRo is the compression ratio

rcrc is the cut off ratio

·         From the above equation, it is observed that, the thermal efficiency of the diesel engine can be increased by increasing the compression ratio, RoRo, by decreasing the cut-off ratio, rcrc, or by using a gas with large value of γ.

·         The efficiency of a Diesel cycle is always lower than that of an Otto cycle having the same compression ratio.

·         However, practical Diesel engines uses higher compression ratios compared to petrol engines and are often quite efficient.

Supercharging:

In I.C. engines supercharging is the process of improving the volumetric efficiency of the engine by using power of engine. In other words it is process of improving the breathing ability of the engine.

Supercharing provides more air in the cylinder (at higher pressure) so that more oxygen in the cylinder results in better combustion and higher efficiency. A compressor using the engine power compresses the atmospheric air that is intaken by the cylinder.

A suction process that uses the compressed air (large quantitiy of air so that large quantity of oxygen) is called as supercharging.

Types of Supercharing:
1) Centrifugal Supercharging
2) Root’s type Supercharging
3) Vane type Supercharing

Methods of Supercharging:

1)  Independently driven compressor or blower

2)  Ram effect

3)  Underposton supercharging

4)  Kadenacy System

5)  Engine driven compressor or blower

Advantages of Superchargine:

1)  High power output

2)  Better atomization of fuel

3)  Better mixing of air and fuel

4)  Better scavanging of products

5)  Quicker acceleration of vehicle

6)  More complete and smoother combustion

7)  Reduce exhaust smoke

8)  Reduced specific fuel comsumption

Limitations of Superchargine:

1)  Increased thermal stresses

2)  Increased heat losses dut to turbulance

3)  Increased gas loading

4)  Increased cooling requirements of piston and valves.

Centrifugal Superchargine:

The centrifugal supercharging draws its power from the movement of the drive where it is attached. The supercharger powers an impeller or small rotating wheel. The impreller draws the air into a small compressor housing (volute) and centrigual force sends the air into the duffuser. The result is air that is highly pressurized but that travels at low speed. The high pressure and low speed air is then fed into the engine where the additional pressure the engine the abilityu ot burn more fuel and have a higher level of cobustion. This results in a faster, more responsive vehicle due to greater engine volumetric efficiency.

Turbocharging:

 The objective of a turbocharger is to improve an engine’s volumetric efficiency by incresing density of the intake air allowing more power per engine cycle. The turbocharger’s compressor draws in ambient air and compresses it before it enters into the intake manifold at increased pressure. The result in a greater mass of air entering the cylinders on each intake stroke. The power needed to spin the compressor is driven from the kinetic energy of the engine exhaust gases.

In automotive applications boost refers to the amount by which intake manifold pressure exceeds atmospheric pressure. This is representative of the extra air presure that is achieved over that would be achieved without the forced induction. The level of boost may be shown on pressure gauge. The control of turbocharger boost has changed dramatically over the 100-plus years of their use. Modern turbochargers can be use westages, blow-off valves and variable geometry.

In petrol engine turbocharger applicatons boost pressure is limited to keep the entire engine system, including the turbocharger , inside its thermal and mechanical design operating range. To avoid engine knocking (detonation) and the related physical demage to engine the intake manifold pressure must not get too high.

Types of turbocharger

1)  Single turbo

2)  Twin turbo

3)  Twin scroll turbo

4)  Variable geometry turbo

5)  Varibale twin scroll turbo

6)  Electric Turbo

Flash point of fuel:

The flash point of a volatile material is the lowest temperature at which vapours of the material will ignite, when given an ignition source. The fire point is always higher than flash point. Sometimes there is confusition between flash point and autoignition point but both are different because the auto ignition point is that point where temperature of fuel is such that that do not need any ignition source of start ignition, but flash point temperature needs ignition source.

Mean Effective Pressure (mep):

Mean effective pressure (mep) is a quantity relating to the operation of a reciprocating engine and is a valuable measure of an engine’s capacity to do work that is independent of engine displacement.

IMEP: When quoted as an indicated mean effective pressure (IMEP) it may be thought of as the average pressure acting on a piston during the different portion of its cycle.

BMEP: Brake mean effective pressure calculated from measure brake torque.

IMEPg: Gross indicated mean effective pressure calculed from calclated from in-cylinder pressure over compression and expansion portion of the engine cycle.

IMEPn: Net indicated mean effective pressure calculated from in-cylinder pressure over the complete cycle.

PMEP: Pumping mean effective pressue from work moving air in and out of the cylinder, across the intake and exhaust valves. Calculated from in-cylinder pressure over intake and exhaust portion of the engine cycle.

FMEP: Friction mean effective pressure required to overcome engine friction can be thought of as mean effective pressure lost due to friction. Friction mean effective pressure calculation requires accureate measurement of cylinder pressure and dynamomerer brake torque.

FMEP = IMEPn – BMEP

Back Pressure:

Back pressure caused by the exhaust system of an automobile engine has negative effect on engine efficiency resulting in a decrease of power output that must be compensated by descrasing fuel consumption.

Specific fuel consumption:

Power developed per unit fuel is called specific fuel consumption.

Brake specific fuel consumption: It is a measure of the fuel efficiency of any prime mover that burns fuel and produces reotational or shaft power. It is tipically used for comparing the efficiency of internal combustion engine with a shaft output.

BSFC = (fuel consumption rate in grams per second)/(power produced in watt)

Thrust specific fuel consumption: It is the fuel efficiency of an engine design with respect to thrust output. TSFC mau also be thought of as fuel consumption per unit thrust.

Specifif Gravity:

Specific gravity is the ratio of density of a substance to the density of referance substance (generally water).

Specific gravity of Petrol = 0.739 at 15.55 degree celcius (60 degree F)
Specific gravity of Diesel = 0.82 to 0.95 at 15.55 degree celcius (60 degree F)

Scavenging:

Scavenging is the process of pushing exhaust gas charge oiut of the cylinder and drawing in a fresh draught of air or air/fuel mixture for next cycle.

There are 3 types of scavenging

1)  Direct or cross flow type scavanging

2)  Reverse type scavenging

3)  Uniflow type scavenging

Cross Flow/ Loop Scavenging:

Cross flow scavengine rake place with the help of piston movement. Cross flow scavengine, transfer prot (inlet) and exhaust port are situated on the opposite side of the cylinder. The exhaust gas is pushed out by cross flow. The piston head is designed to have a hump shape called deflector. The fresh air enters in the engine cylinder is deflected to the upward by a deflector and pushing exhaust gas down the other side. Before loop scavanging invented, almost all two-stroke engines use this method. In practice the gas flow failed to follow the idealised pattern. The rib of the deflector piston also a poor shape for the combustion chamber with long flame paths and excessive surface are. This method of scavenging has now beed almost entirely replaced by loop scavanging.

Although obsolute for piston ported two stroke engines cross-flow scavanging is now commmon in four stroke engines where their inlet and exhaust valves are mounted on opposite sides of cylinder head. As the inlet and exhaust strokes of four stroke cycle happen on different strokes of piston the upward exhaust stroke pushing gases out is followed by the downward inlet stroke allowing the fresh charge in the flow is as tow isolated isnle flow rather than as an unstable loop.

Advantage-

-    Low Manufacturing cost

-    Good scavenging at low speed and part throttle.

-    Low engine volume for the multicylinder arrangemet.

Disadvantages-

-    Heavy piston with very high heat absorption

-    High tendency to knock

-    Poor scavanging at high speed and full throttle

-    Compulsory water cooling, diffuculty in cooling piston crown.

Reverse tye/ Backflow/Schnuerle porting Scavenging:

Rather than the flow loop being vertical, the gases asre encouraged to move in two horizontal loops. In this method, the inlet and outlet ports are suited on the same side of the cylinde. The fresh charge while entering into cylinder forms a loop and pushed out the burnt gases.

Advantage-

-    Low maintenance

-    The low surface area to the volume of the cylinder hence the heat lodd reduced

-    Good scavenging at full throttle

-    Water cooling system not necessary.

Disadvantages-

-    Poor scavenging at part throttle operation

-    Scavengine time is short.

Uniflow Scavenging:

In this method the scavenging the fresh charge while entering from one side (or sometimes two sides) of the cylinder pushes out the gases through the exit valce situated on the top of the cylinder. In this both the fresh charge and burnt gases move in same direction. Usually in deisel type eingine the directrion of flow is upward but with spark ignition einginies such as the Ricardo dolphin the direction of flow is generally downward with fresh charge entering at top of engine. It is widely used for two stroke engines and locomotive engines.

Advantages-

-    Extended time for valve operation

-    The possibility of mixing is reduced due to uniflow

-    Increse power output

-    Most efficient of all three methods of scavenging

-    Good scavenging at all speed ranges and throttle position

-    Low fuel comsumption compared to other scavenging types.

Disadvantages-

-    Elaborate and costly construction

-    Difficulty in cooling the piston

Air Filters/Cleaners:

A particulate air filter is a device composed of fibrous or porous materials which removes solid particulates such as dust, pollen, mold and bacteria from the air. Filters containing an absorbent or catalyst such as charcoal my alos remove odors and gaseous pollutant such as volatile organic compounds. Air filters are used in application where air quality is important, notably in building ventilation system and in engines.

Photochemical smog:

It is a type of smog or air pollutant derived from vehicle emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emission to form photochemical smog.

§  For maximum power genration the air fuel raito for a pertol engine for vehicle is of order of 12:1.

§  Air fuel ratio for idling speed of a petrol engine is approximately 10:1.

§  The theoritically correct air-fuel ratio for petrol engine is of order of 15:1.

§  Volatility of diesel fuel oil is indicated by 90% distillation temperature i.e. when 90% of sample oil has distilled off.

§  Stiochiometric air-fuel ratio is chemically correct mixture.

§  Ignition quality of petrol is expressed by octane number.

§  Petrol is distilled at temperature in range of 65-220 degree celcius.

§  Kerosene is distilled at 220-350 degree celcius.

§  Self ignition temperature of petrol is more than 500 degree celcius.

§  Iso-octance has octance number of 100.

§  Octance number is determined by comparing the performance of the pertol wth hydrocarbons of mixture of normal heptance and iso-octance.

§  Centane is a straight chain peraffin.

§  Ethul fluid is used to increase in octance rating of the fuel.

§  Self ignition temperature of diesel oil compared to pertol is higher.

§  Normal heptane accelerates auto ignition.

§  Cetance humber is determined by comparing the performance of diesel woil with the nydrocarbon of mixture of cetance and alphamethyl nepthalene.

§  Violent sound pulsation within the cylinder of an I.C. engines are caused due to detonation.

§  Auto ignition temperatue is that at which it catches fire without external aid.

§  Ignition lag is the time taken by fuel after injection to reach upto auto ignition temperature.

§  The spark plug gap is normally maintained at 0.45 to 0.6 mm.

§  The delay period in petrol engine is of order of 0.002 second.

§  Detonation is caused by peroxides, aldehydes and ketones.

§  If overhead clearance is less then horzontal engine should be selected.

§  Piston rings are plated with chromium, cadmium or phosphate in order to reduce wear and eliminate scuffing.

§  In order to prevent knock in S.I. engines the charge away from the spark plug should have low temperature low density, long ignition delay and rich mixture.

§  To reduce the possibility of knock in the C.I. engines the first element of fuel and air should have high temperatue, high density, short delay and reactive mixture.

§  Accouding to Recordo’s theroy detonation occures due to instataneous aouto ignition of last part of charge to be burnt.

§  The ignition of charge by some hot surgace in the engine cylinder before operationof spark flug is known as pre ignition.

§  Ignition lag is time before actual fuel injection and the pump pluger starts to pump fuel.

§  For best results of efficent comustion, high speed diesel engines need an approximate centane no of 50.

§  Calorific value of diesel oil is 15000 kcal/Kg

§  Carbon resideual in diesel oil should not be more than 0.1%.

§  The sepcific gravity of diesel oil is 0.85.

§  Freezing temperature of petrol is less than -30 degree celcius.

§  The specific gravity of petrol is 0.75.

§  Detonation can be controlled by retarding the spark timing.

§  The efficiency of I.C. engines normally is of the order of 30-35%.

§  Sulphur content in diesel oil should not be more than 1%.

§  The m.e.p. of a diesel cycle having fixed compression ratio with increase in cut off ratio will increase.

§  Ignition timeing of a multi cylinder petrol engine can be adjusted by rotating the distrubutor.

§  Fuel consumption with increase in back pressure will incerease.

§  Leakage past te piston rings and valuve seats in I.C. engines with increase in speed decrease.

§  The function of a distrubutor in an automobile is to time the spark.

§  The system of lubrication used for motor cycle and scooters is by mixing 5% lubricating oil with petrol.

§  The thermal efficiency of a two stroke engine as compared to four stroke engine is less.

§  Diesel engine as compared to petrol engine require bigger flywheel.

§  The minimum value of auto ignition occurs in the region of chemicaly correct fuel-air ratio.

§  The tendency of a diesel engine to knock increase if compression ratio is increased.

§  The tendency of a petrol engine to knock increase by supercharging.

§  The brake mean effective pressure of an I.C. engine with increase in speed wil remain unaffected.

§  In petrol engine, Nitrogen as gets exhausted out without burning and without transformation.

§  The level of fuel in the float chamber of a carburator as compared to the level of the jet in the venturi is lower.

§  In carburator the top of the fuel jet with referance to the level in the float chamber is kept at slightly higher level.

§  Power impulse from I.C. engine are smoothed out by flywheel.

§  Deposition of carbon in petrol engine cylinder would result in increase in compression ratio.

§   If petrol is used in a diesel engine then higher knocking will occur.

§  In turbulence chamber in diesel engine fuel is injected into an auxiliary chamber that is separated from the cylinder by an orifice or throat.

§  For low load operation C.I. engine is more suitable.

§  For the same size and weight a two stroke engine as compared to four stroke engine will generate power about 1.7 times.

§  The thermal efficiency of a semi-diesel cycle having fixed compression ratio and fixed quantity of heat with increase in pressure ratio will increase.

§  In a diesel engine injection pressure developed by injector is of the order of 1400 Kg/M^3.

§  The bi-fuel engine uses liquid fuel during start up and gas as the basic fuel.

§  Morse test us used to determine mechanical efficiency of multicylinder engines.

§  During idling stage gasoline does not flow through the carburator tube because of ventruri vaccum.

§  Thermal efficiency of I.C. engine on weak mixture is higher.

§  In petrol engine the actual pressure developed compared to the preducted maximu pressure is 50%.

§  Octance number of petrol normally used in petrol engine is of order of 80-90.

§  Octance number of petrol available from Indian refineries of the order of 13.

§  In spark ignition engines the knocking tendency can be decreased by adding dopes like tetraethyl lead and ethylene dibromide.

§  Performance number are indicative of th fuels having antiknock quantities superior to iso-octance.

§  Four stroke petrol engines as compared to two stroke petrol engine having same output rating and same compression ratio have higher thermal efficiency.

§  The cetance number of diesel oil generally available is of the order o 55-70.

§  High speed diesel engine need a cetane number o 50.

§  Speed droop is the decrease in engine speed from no load to full load.

§  Cetance number is the measure o ignition quality.

§  Indicated power = Brake power + Friction Power

§  The antifreeze solution commonly used in automibiles is glycol.

§  The power to weight ratio in a two stroke engine as compared to four stroke engine is more.

§  Freezing temperature of petrol is -50 to -30 degree celcius.

§  Injection lag in diesel engine is caused by expansion of fuel oil discharge lines under high pressure, compressibility of fuel and leakage past the fuel-oil plenger.

§  The piston of diesel engine are usually cooled by lubricating oil.

§  The backpressure of petrol engine is usually of the order of 1.2ata.

§  Muffler is used to reduce exhaust noise.

§  The specific fuel consumption is espressed as the fuel consumed per hour per unit brake horse power.

§  Higher calorific value of a fuel is based on the assumption that water is present in vapoir from.

§  In case of compound engine, equal power is developed by each lylinder with a view to obtain uniform turning moment.

§  The compression ratio is kept low in pertol engine compared tro a diesel because higher compression ratio in petrol engine would lead to preignition of fuel.

§  A temperature indicator is usualy procided for automobiles. It indicates temperature of jacket cooling water.

§  The lead-acid type of battery is commly used in automobile application.

§  The gear ration in a differential unit of a passenger car is of order of 3:1.

§  The acid used in automobile battery is H2SO4.

§  Ignition accelerators are substances which increases the rate of preflame reaction and reduce the ignition lag.

§  n-heptane accelerates auto-ignition and iso-octane helps to resist auto ignition.

§  Petrol engines are not suitable for part load operaiton because mechanical efficiency is poor due to increasing internal losses at incresed throttling.

§  The power to weight ratio of diesel engine compred to petrol engine is low.

§  Flash point for diesel fuel should be minimum 49 degree celcius.

§  Vapour lock is complete or partial stoppage of fuel supply due to vaporization of fuel in supply system.

§  By higher octance number of S.I. fuel, it mean that the fuel has lower volatility.

§  Keeping other parameter constant brake power of diesel engine can be increased by increasing the pressur eo intake air.

The Decline of the Mughal Empire

The Decline of the Mughal Empire

The great Mughal empire, the envy of its contemporaries for almost two centuries, decline and disintegrated during the first half of the 18^th century. The Mughal emperors lost their power and glory and their empire shrank to a few square miles around Delhi. In the end, in 1803, Delhi itself was occupied by the British army and the proud Mughal emperor was reduced to the status of a mere pensioner of a foreign power. A study of the process of decline of this great empire is most instructive. It reveals some of the defects and weaknesses of India’s medieval social, economic and political structure which were responsible for the eventual subjugation of the country by the English East India Company.

            The unity and stability of the empire had been shaken up during the long and strong reign of Aurangzeb; yet in spite of his many harmful policies, and Mughal administration was still quite efficient and the Mughal army quite strong at the time of his death in 1707. Moreover, the Mughal dynasty still respect in the country.

            On Aurangzeb’s death his three sons fought among themselves for the throne. The 65 years old Bahadur Shah emerged victorious. He was learned, dignified, and able. He followed a policy of compromise and conciliation, and there was evidence of the reversal of some of the narrow-minded policies and measures adopted by Aurangzeb. He adopted a more tolerant attitude towards the Hindu chiefs and Rajas. There was no destruction of temples in his reign. In the beginning, he made an attempt to gain greater control over the Rajput states of Amber and Marwar (Jodhpur) by replacing Jai Singh with his younger brother Vijai Singh at Amber and by forcing Ajit Singh of Marwar to submit to Mughal authority. He also made an attempt to garrison the cities of the Amber and Jodhpur. This attempt was, however, met with firm resistance. This may have made him recognize the folly of his actions for he soon arrived at a settlement with the two states, though the settlement was not magnanimous. Though their states were restored to the Rajas Jai Singh and Ajit Sigh, their demand for high “Mansabs” and the offices of “Subahdars” of important provinces such as Malwa and Gujarat was not accepted.

            His policy towards the Maratha Sardars was that of half-hearted conciliation. While he granted them the “Sardeshmukhi” of Deccan, he failed to grant them the “Chauth” and to satisfy them fully. He also did not recognize Shahu as the rightful Maratha King. He thus let Tara Bai and Shahu fight for supremacy ovewas that the Maratha Kingdom. The result was that Shahu and the Maratha Sardars remained dissatisfied and the Deccan continued to be susceptible to disorder. There could be no restoration of peace and order as the Maratha Sardars fought one another as well as against the Mughal authority.

            Bahadur Shah had tried to conciliate the rebellious Sikhs by making peace with Guru Gobind Singh and giving him a high “Mansab”. But when, after the death of Guru Gobind Singh, the Sikhs once again raised the banner of revolt in the Punjab under the leadership of Banda Bahadur, the emperor decided to take strong measures and himself led a campaign against the rebels, who soon controlled practically the entire territory between the Sutlej and the Jamuna, reaching the close neighborhood of Delhi. Even though he succeeded in capturing Lohgarh, a fort built by Guru Gobind Singh north-east of Ambala at the foothills of the Himalayas, and other important Sikh strongholds, the Sikhs could not be crushed and in 1712, they recovered the fort of Lohgarh.

            Bahadur Shah conciliated Chatarsal, the Bundela chief, who remained a loyal feudatory, and the Jat chief Churaman, who joined him in the campaign against Banda Bahadur.

            There was further deterioration in the field of administration in Bahadur Shah’s reign. The position of state finances worsened as a result of his reckless grants of “Jagirs” and promotions. During his reign the remnants of the royal treasure amounting in 1707 to some 13 crores of rupees, were exhausted.

            Bahadur Shah was groping towards a solution of the problems besetting the empire. Given time, he might have revived the imperial fortunes. Unfortunately, his death in 1712 plunged the empire once again into civil war.

            A new element entered Mughal politics in this and the succeeding wars of succession. While previously the contest for power had been between royal princes, and the nobles had merely aided the aspirants to the throne, now ambitious nobles became direct contenders for power and used princes as mere pawns to capture the seats of authority. In the civil was following Bahadur Shah’s death, one of the his less able son, Jahandar Shah, won because he was supported by Zulfiqar Khan, the most powerful noble of the time.

            Jahandar Shah was weak and degenerate prince who was wholly devoted to pleasure. He lacked good manner and dignity and decency. During his reign, the administration was virtually in the hands of the extremely capable and energetic Zulfiqar Khan, who had become his Wazir. Zulfiqar Khan believed that it was necessary to establish friendly relations with Rajput Rajas and the Maratha Sardars and to conciliate the Hindu chieftains in general in order to strengthen his own position at the Court and to save the empire. Therefore, he rapidly reversed the policies of Aurangzeb. The hated “Jizhay” was abolished. Jai Singh of Amber was given the title of Mirza Raja Sawai and appointed governor of Malwa; Ajit Singh of Marwar was awarded the title of Maharaja and appointed governor of Gujarat. Zulfiqar Khan confirmed the earlier private arrangement that his deputy in the Deccan, Daud Khan Panni, had concluded with the Maratha King Shahu in 1711. By this arrangement, the Maratha ruler was granted the “Chauth and Sardeshmukhi” of the Deccan on the condition that these collections would be made by Mughal officials and rhen handed over to the Maratha officials. Zulfiqar Khan also conciliated Churaman Jat and Chhatarsal Bundela. Only towarda Banda and the Sikhs did he continue the old policy of suppression.

            Zulfiqar Khan made an attempt to improve the finances of the empire by checking the reckless growth of Jagirs and offices. He also tried to compel the Mansabdars to maintain their official quota of troops. An evil tendency encouraged by him was that of “Ijarah” of revenue-farming. Instead of collecting land revenue at a fixed rate as under Todar Mal’s land revenue settlement, the government began to contract with revenue farmers and middlemen to pay the government a fixed amount of money while they were left free to collect whatever they could from the peasant. This led to increased oppression of the peasant.

            Many jealous nobles secretly worked against Zulfiqar Khan. Worse still, the emperor too did not give his trust and cooperation in full measure. The emperor’s ears were poisoned against Zulfiqar Khan by unscrupulous favorites. He was told that his Wazir was becoming too powerful and ambitious and might even overthrow himself. The cowardly emperor dared not dismiss the powerful Wazir, but he began to intrigue against his secretly. Nothing could have been more destructive of healthy administration.

            Jahandar Shah’s inglorious reign came to an early end in January 1713 when he was defeated at Agra by Farrukh Siyar, his nephew. Farrukh Siyar owned his victory to the Saiyid Brothers, Abdullah Kahn and Husain Ali Khan Baraha, who were therefore given the offices of Wazir and Mir Bakshi respectively. The two brothers soon acquired dominant control over the affairs of the state. Farrukh Siyar lacked the capacity to rule. He was cowardly, cruel, undependable and faithless. Moreover, allowed himself to be influenced by worthless favorites and flatterers.

            In spite of his weaknesses, Farrukh Siyas was not willing to give the Saiyid brothers a free hand but wanted to exercise personal authority. On the other hand, the Saiyid brothers were convinced that administration could be carried on properly, the decay of the empire checked, and their own position safeguarded only if they wielded real authority and the emperor merely reigned without ruling. Thus there ensued a prolonged struggle for power between the Emperor Farrukh Siyar and his Wazir and Mir Bakshi. Year after year the ungrateful emperor intrigued to overthrow the two brothers; year after year, he failed. In the end, in 1719, the Saiyid Brothers now made the 18-year-old Mahammad Shah the emperor of India. The successor of Farrukh Siyar were mere puppets in the hands of the Saiyids. Even their personal liberty to meet people and to move around was restricted. Thus from 1713 until 1720, when they were overthrown, the Saiyid brothers wielded the administrative power of the state.

            The Saiyid brothers adopted the policy of the religious tolerance. They believed that India could be ruled harmoniously only by associating Hindu chief and nobles with the Muslim nobles in governing the country. Again, they sought to conciliate and use the Rajputs, the Marathas, and the Jats in their struggle against Farrukh Siyar and the rival nobles. They abolished the Jizyah immediately after Farrukh Siyar’s accession to the throne. Similarly, the pilgrim tax was abolished from a number of places. They won over to their side Ajit Singh of Marwae, Jai Singh of Amber, and many other Rajput princes by giving them high position of influence in the administration. They made an alliance with Churaman, the Jat chieftrain. In the later years of their administration they reached an agreement with King Shahu by granting him the Swarajya (of Shivaji) and the right to collect the Chauth and Sardeshmukhi of the six provinces of the Deccan. In return, Shahu agreed to support them in the Deccan with 15000 mounted soldiers.

            The Saiyid brothers made a vigorous effort to contain rebellions and to save the empire from administrative disintegration. They failed in these tasks mainly because they were faced with constant political rivalry, quarrels, and conspiracies at the court. This continued friction in the ruling circles disorganized and even paralyzed administration at all levels. Lawlessness and disorder sprayed everywhere They financial position of re state deteriorated rapidly as Zamindars and rebellious element refused to pay land revenue, officials misappropriated state revenues, and central income declined because of the spread of revenue farming. As a result, the salaries of the officials and soldiers could not be paid regularly and the soldiers became undisciplined and even mutinous. 

            Even though the Saiyid brothers had tried hard to conciliate and befriend all sections of the nobility, a powerful group of nobles headed by Nizam-ul-Mulk and his father’s cousin Muhamad Amin Khan began to conspire against them. These nobles were jealous of the growing power of the brothers. The deposition and murder of Farrukh Siyar frightened many of them; if the emperor could be killed, what safety was there for mere nobles? Moreover, the murder of the emperor created a wave of public revulsion against the two brothers. They were looked down upon as traitors – persons who had not been ‘true to their salt’ (namak haram). Many of the nobles of Aurangzeb’s reign also disliked the Saiyid alliance with the Rajput and the Maratha chiefs and their liberal policy towards the Hindus. There nobles declared that Saiyids were following anti-Mughal and anti-Islamic policies. They tried to arouse the fanatical sections of the Muslim nobility against the Saiyid brothers. The anti-Saiyid nobles were supported by emperor Muhammad Shah who wanted to free himself from the control of the two brothers. In 1720, they succeeded in treacherously assassinating Husain Ali Kahn, the younger of the two brothers. Abdullah Khan tried to fight back but was defeated near Agra. Thus, ended the domination of the Mughal empire by the Saiyid brothers known in Indian history as ‘King Maker’.

            Mohammad Shah’s long reign of nearly 30 years (1719-48) was the last chance of saving the empire. There were no quick chances of imperial authority as in the period 1707-20. When his reign began Mughal prestige among the people was still an important political factor. The Mughal army and particularly the Mughal artillery was still a force to rack on with. Administration in northern India had deteriorated but not broken down yet. The Maratha sardars were still confined to the South, while the Rajput rajas continued to be loyal to the Mughal dynasty. A strong and farsighted ruler supported by nobility conscious of its peril might still have saved the situation. But Muhammad Shah was not the man of the moment. He was weak-minded and frivolous and over fond of a life of ease and luxury. He neglected the affairs of state. Instead of giving full support to able Wazir such as Nizam-ul-Mulk, he fell under the evil influence of corrupt and worthless flatterers and intrigued against his own ministers.  He even shared in the bribes taken by his favorite countries.

            Disgusted with the fickle-mindedness and suspicious nature of the emperor and the constant quarrels at the court, Nizam-ul-Mulk, the most powerful noble of the time, decided to follow his own ambition. He had become the Wazir in 1722 and made a vigorous attempt to reform the administration. He now decided to leave the emperor and his empire to their fate and to strike out on his own. He relinquished his office in October 1724 and marched south to found the state of Hyderabad in the Deccan. ‘His departure was symbolic of the flight of loyalty and virtue from the empire.’’ The physical break-up of the Mughal empire had begun.

            The other powerful and ambitious nobles also began to utilize their energies for carving out semi-independent states. Hereditary nawabs owing nominal allegiance to the emperor at Delhi arose in many parts of the country, for example, in Bengal, Hyderabad, Avadh, and the Punjab. Everywhere petty Zamindars, Rajas and Nawabs raised the banner of rebellion and independence. The Maratha Sardars began their northern expansion and overran Malwa, Gujarat and Bundelkhand. Then, in 1738-39, Nadir Shah descended upon the plains of northern India, and empire lay prostrate.

            Nadir Shah had risen from shepherd boy to Shah (King) by saving Persia from sure decline and disintegration. In the beginning of the eighteenth-century Persia, hitherto a powerful and far flung empire, was under the weak rule of the declining Safavi dynasty. It was threatened by internal rebellions and foreign attacks. In the east, the Abdali tribesmen revolted and occupied Herat, and the Ghalzai tribesmen detached the province of Qandahar. Similar revolts occurred in the north and west. In Shirvan, religious persecution of the Sunnis by fanatical Shias led to rebellion. Here, “Sunni mullahs were put to death, mosques were profaned and turned into stables, and religious works were destroyed.” In 1721, the Ghalzai chief of Qandahar, Muhamud, invaded Persia and occupied Isfahan, the capital. Russia under Peter the great was determined to push southward. Peter began his invasion of Persia in July 1722 and soon forced Persia to sign away serveral of her provinces on the Caspian Sea, including the town of Baku. Turkey, deprived of most of her European possessions, also hoped to make good the loss at Persia’s cost. IN the spring of 1723, Turkey declared war on Persia and rapidly pushed through Georgia and then penetrated south. In June 1724, Russia and Turkey signed a treaty dividing all northern and most of western Persia between them. At this stage, in 1726, Nadir emerged as a major supporter of Tahmsap and as his most brilliant commander. In 1729 he won back Herat after defeating the Abdalis and expelled the Ghalzais fro Isfahan and central and southern Persia. After long and bitter warfare, he compelled Turkey to give back all conquered territory. The following year, he deposed the last of the Safavi rulers and made himself the Shah. In the following years, he reconquered the province of Qandahar.

            Nadir Shah was attracted to India by the fabulous wealth for which it was always famous. Continual campaigns had made Persia virtually bankrupt. Money was needed desperately to maintain his mercenary army. Spoils from India could be a solution. At the same time, the visible weakness of the Mughal empire made such spoliation possible. He entered Indian territory towards the end of 1738, without meeting any opposition. For years the defenses of the north-west frontier had been neglected. The danger was not fully recognized till the enemy had occupied Lahore. Hurried preparations were then made for the defense of Delhi, but the faction-ridden nobles refused to unite even in sight of the enemy. They could not agree on a plan for defense or on the commander of the defending forces. Disunity, poor leadership, mutual jealousies and distrust could lead only to defeat. The two armies met at Karnal on 13 February 1739 and invader inflicted a crushing defeat on the Mughal army. The emperor Muhammad Shah was taken peisoner and Nadir Shah marched on to Delhi.

Welding Defects

Most Common Types of Welding Defects

 Incomplete Penetration

Incomplete penetration happens when your filler metal and base metal aren’t joined properly, and the result is a gap or a crack of some sort. Check out the Figure below for an example of incomplete penetration.

Welds that suffer from incomplete penetration are weak at best, and they’ll  likely fail if you apply much force to them. (Put simply, welds with incomplete  penetration are basically useless.)
Here’s a list of the most common causes of incomplete penetration welding defect.

The groove you’re welding is too narrow, and the filler metal doesn’t
reach the bottom of the joint.

✓ You’ve left too much space between the pieces you’re welding, so they
don’t melt together on the first pass.
✓ You’re welding a joint with a V-shaped groove and the angle of the
groove is too small (less than 60 to 70 degrees), such that you can’t
manipulate your electrode at the bottom of the joint to complete
the weld.
✓ Your electrode is too large for the metals you’re welding.
✓ Your speed of travel(how quickly you move the bead) is too fast, so
not enough metal is deposited in the joint.
✓ Your welding amperage is too low.If you don’t have enough electricity
going to the electrode, the current won’t be strong enough to melt the
metal properly

 Incomplete Fusion

Incomplete fusion occurs when individual weld beads don’t fuse together, or  when the weld beads don’t fuse properly to the base metal you’re welding,  such as in below.

The most common type of incomplete fusion is called overlap and usually  occurs at the toe(on the very top or very bottom of the side) of a weld. One of the top causes is an incorrect weld angle, which means you’re probably holding the electrode and/or your filler rods at the wrong angle while you’re making a weld; if you think that’s the case, tweak the angle a little at a time until your overlap problem disappears.

Here are a few more usual suspects when it comes to incomplete fusion
causes.

✓ Your electrode is too small for the thickness of the metal you’re welding.
✓ You’re using the wrong electrode for the material that you’re welding.
✓ Your speed of travel is too fast.
✓ Your arc length is too short.
✓ Your welding amperage is set too low.
If you think your incomplete fusion may be because of a low welding amperage, crank up the machine! But be careful: You really need only
enough amperage to melt the base metal and ensure a good weld.
Anything more is unnecessary and can be dangerous.
✓ Contaminants or impurities on the surface of the parent metal(the metal
you’re welding) prevent the molten metal (from the filler rod or elsewhere
on the parent metal) from fusing.

Undercutting

Undercutting is an extremely common welding defect. It happens when your  base metal is burned away at one of the toes of a weld. To see what I mean, look at Figure.

When you weld more than one pass on a joint, undercutting can occur between the passes because the molten weld is already hot and takes less heat to fill, yet you’re using the same heat as if it were cold. It’s actually a very serious defect that can ruin the quality of a weld, especially when more than 1⁄32 inch is burned away. If you do a pass and notice some undercutting, you must remove it before you make your next pass or you risk trapping slag (waste material — see the following section) into the welded joint (which is bad news). The only good thing about undercutting is that it’s extremely easy to spot after you know what you’re looking for.

Here are a few common causes of undercutting:
✓ Your electrode is too large for the base metal you’re welding.
✓ Your arc is too long.
✓ You have your amperage set too high.
✓ You’re moving your electrode around too much while you’re welding.
Weaving your electrode back and forth is okay and even beneficial, but if
you do it too much, you’re buying a one-way ticket to Undercutting City
(which is of course the county seat for Lousy Weld County).

Slag Inclusions

A little bit of slag goes a long way . . . toward ruining an otherwise quality weld. Slagis the waste material created when you’re welding, and bits of this solid material can become incorporated (accidentally) into your weld, as in Figure . Bits of flux, rust, and even tungsten can be counted as slag and can cause contamination in your welds.

Common causes of slag inclusions include

✓ Flux from the stick welding electrode that comes off and ends up in the
weld
✓ Failure to clean a welding pass before applying the next pass
Be sure to clean your welds before you go back in and apply a second weld bead.
✓ Slag running ahead of your weld puddle when you’re welding a V-shaped
groove that’s too tight
✓ Incorrect welding angle
✓ Welding amperage that’s too low

Flux Inclusions

If you’re soldering or brazing (also called braze welding), flux inclusions can be a real problem. If you use too much flux in an effort to “float out” impurities from your weld, you may very well end up with flux inclusions like those in Figure . (Head to Chapter 13 for more on brazing and soldering.)

If you’re working on a multilayer braze weld, flux inclusion can occur when you fail to remove the slag or glass on the surface of the braze before you apply the next layer. When you’re soldering, flux inclusion can be a problem if you’re not using enough heat. These inclusions are usually closely spaced, and they can cause a soldered joint to leak. If you want to avoid flux inclusions (and believe me, you do), make sure you do the following:
✓ Clean your weld joints properly after each pass.This task is especially
important when you’re brazing.
✓ Don’t go overboard with your use of flux.
✓ Make sure you’re using enough heat to melt the filler or flux material.

Porosity

If you read very much of this book, you quickly figure out that porosity(tiny holes in the weld) can be a serious problem in your welds (especially stick or mig welds). Your molten puddle releases gases like hydrogen and carbon dioxide as the puddle cools; if the little pockets of gas don’t reach the surface before the metal solidifies, they become incorporated in the weld, and nothing can weaken a weld joint quite like gas pockets. Take a gander at Figure  for an example of porosity.

Following are a few simple steps you can take to reduce porosity in your
welds:
✓ Make sure all your materials are clean before you begin welding.
✓ Work on proper manipulation of your electrode.
✓ Try using low-hydrogen electrodes.

Cracks

Cracks can occur just about everywhere in a weld: in the weld metal, the plate next to the weld metal, or in any other piece affected by the intense heat of welding. Check out the example of cracking in Figure.

Here are the three major types of cracks, what causes them, and how you can prevent them.

✓ Hot cracks:

This type of crack occurs during welding or shortly after you’ve deposited a weld, and its cause is simple: The metal gets hot too
quickly or cools down too quickly. If you’re having problems with hot cracking, try preheating your material. You can also postheat your material, which means that you apply a little heat here and there after you’ve finished welding in an effort to let the metal cool down more
gradually.

✓ Cold cracks:

This type of crack happens well after a weld is completed and the metal has cooled off. (It can even happen days or weeks after a
weld.) It generally happens only in steel, and it’s caused by deformities in the structure of the steel. You can guard against cold cracking by
increasing the thickness of your first welding pass when starting a new weld. Making sure you’re manipulating your electrode properly, as well as pre- and postheating your metal, can also help thwart cold cracking.

✓ Crater cracks:

These little devils usually occur at the ending point of a weld, when you’ve stopped welding before using up the rest of an
electrode. The really annoying part about crater cracks is that they can cause other cracks, and the cracking can just kind of snowball from
there. You can control the problem by making sure you’re using the appropriate amount of amperage and heat for each project, slowing your
speed of travel, and pre- and postheating.

Warpage

If you don’t properly control the expansion and contraction of the metals you work with, warpage(an unwanted distortion in a piece of metal’s shape) can be the ugly result. Check out an example in Figure.

If you weld a piece of metal over and over, the chances of it warping are much higher. You can also cause a piece of metal to warp if you clamp the joints too tightly. (If you allow the pieces of metal that make the joint to move a little, there’s less stress on them.)
Say you’re welding a Tjoint. The vertical part of the Tsometimes pulls itself toward the weld joint. To account for that movement, simply tilt the vertical part out a little before you weld, so that when it tries to pull toward the weld joint, it pulls itself into a nice 90-degree angle!
The more heat you use, the more likely you are to end up with warpage, so be sure to use only the amount of heat you need. Don’t overdo it. Opting for a slower speed of travel while welding can also help to cut down on warpage.

Spatter

Spatter(small particles of metal that attach themselves to the surface of the material you’re working on.) is a fact of life with most kinds of welding; no matter how hard you try, you’ll never be able to cut it out completely. You can see it in all its glory in Figure 11-5 in Chapter 11.
You can keep spatter to a minimum by spraying with an anti-spatter compound (available at your welding supply store) or by scraping the spatter off the parent metal surface.