According to Operating Cycles.According to Operating Cycles.

(a) (a) OTTO CYCLE (Constant Volume OTTO CYCLE (Constant Volume Combustion CycleCombustion Cycle). ).

It is the ideal air standard cycle for Petrol It is the ideal air standard cycle for Petrol engine, the gas engine and the high-speed engine, the gas engine and the high-speed oil engine. The engines based on this cycle oil engine. The engines based on this cycle have high thermal efficiency but noisiness have high thermal efficiency but noisiness results particularly at higher power due to results particularly at higher power due to higher pressures in the cylinders. higher pressures in the cylinders.

Otto cycleOtto cycle

T = temperatureS = Entropy

Constant volume cycle

1-2 isentropic compression

2-3 heat addition at constant

volume

3-4 isentropic expansion

4-1 heat rejection at constant volume

Air standard thermal efficiency = 1-(1/r) , r = comp. Ratio.

entropy (n) measure of the entropy (n) measure of the unavailability of a system's thermal unavailability of a system's thermal energy for conversion into energy for conversion into mechanical work. [Greek: related to mechanical work. [Greek: related to *en-2, trope transformation]*en-2, trope transformation]

(b) (b) DIESEL CYCLE (Constant Pressure DIESEL CYCLE (Constant Pressure Combustion Cycle).Combustion Cycle).

It is the ideal Air standard cycle for Diesel It is the ideal Air standard cycle for Diesel Engine, especially suitable for low speed Engine, especially suitable for low speed Diesel Engine but not for high speed Diesel Diesel Engine but not for high speed Diesel Engine. (The thermal efficiency is lower Engine. (The thermal efficiency is lower than Otto cycle engines but engines run than Otto cycle engines but engines run smoothly due to lower pressures in the smoothly due to lower pressures in the cylinder. cylinder.

(c) (c) DUAL COMBUSTION CYCLE (Constant DUAL COMBUSTION CYCLE (Constant Pressure and Constant Volume Combustion Pressure and Constant Volume Combustion Cycle).Cycle).

Modern Diesel Engines do not operate purely Modern Diesel Engines do not operate purely on constant pressure combustion cycle but on constant pressure combustion cycle but some part of combustion process takes some part of combustion process takes place at constant volume while the rest is place at constant volume while the rest is completed at constant pressure. completed at constant pressure.

In general, this cycle resembles Constant In general, this cycle resembles Constant volume combustion Cycle more than volume combustion Cycle more than constant pressure combustion cycle. It is constant pressure combustion cycle. It is suitable for modern Medium and High suitable for modern Medium and High Speed Diesel Engines. The thermal Speed Diesel Engines. The thermal efficiency is more than Diesel Cycle but less efficiency is more than Diesel Cycle but less than Otto cycle. Also noise level is in than Otto cycle. Also noise level is in between the two. This is a more practical between the two. This is a more practical engine. engine.

Dual combustionDual combustion

Mixed cycle of otto and diesel cycle

Heat added partly at constant volume and partly at constant pressure.

hence having advantages of both cycles.

According to Strokes/Cycle.According to Strokes/Cycle.In an engine, the following events form a cycle: In an engine, the following events form a cycle: Filling the engine cylinder with fresh air. Filling the engine cylinder with fresh air. Compressing the air so much that injected fuel ignited Compressing the air so much that injected fuel ignited

readily by coming in contact with hot air and burns readily by coming in contact with hot air and burns efficiently.efficiently.

Combustion of fuel.Combustion of fuel.Expansion of hot gases.Expansion of hot gases.Emptying the products of combustion from the cylinder. Emptying the products of combustion from the cylinder. Depending on how many strokes of piston are required Depending on how many strokes of piston are required

in completing this cycle, the engines can be divided in completing this cycle, the engines can be divided into two classes: into two classes:

1. 1. Four Stroke Engine Four Stroke Engine An engine, which needs 4 strokes of the piston (2 in An engine, which needs 4 strokes of the piston (2 in

and 2 out) to complete one cycle, is called Four-and 2 out) to complete one cycle, is called Four-stroke engine. stroke engine.

2. 2. Two Stroke Engine Two Stroke Engine An engine that needs only 2 strokes of the piston (1 in An engine that needs only 2 strokes of the piston (1 in

and 1 out) to complete one cycle is called Two-stroke and 1 out) to complete one cycle is called Two-stroke engine. engine.

According to Piston Connection. According to Piston Connection.

Trunk Piston TypeTrunk Piston Type..

The piston is connected directly to the upper The piston is connected directly to the upper end of the connecting rod. A horizontal pin end of the connecting rod. A horizontal pin (Gudgeon Pin) within piston is encircled by (Gudgeon Pin) within piston is encircled by the upper end of the connecting rod. This the upper end of the connecting rod. This construction is quite common, especially construction is quite common, especially in small and medium size engines. in small and medium size engines.

(b) (b) Cross Head TypeCross Head Type. . The piston fastens to a vertical piston The piston fastens to a vertical piston

rod whose lower end is attached to a rod whose lower end is attached to a ‘cross head’, which slides up and ‘cross head’, which slides up and down in guides. The crosshead down in guides. The crosshead carries a crosshead pin, which is carries a crosshead pin, which is encircled by the upper end of the encircled by the upper end of the connecting rod. This more connecting rod. This more complicated construction is common complicated construction is common in double acting engines and large in double acting engines and large slow speed single acting engines. slow speed single acting engines.

Comparison between Trunks Piston Comparison between Trunks Piston Versus Cross Head EngineVersus Cross Head Engine. .

Most medium and small size engines use trunk Most medium and small size engines use trunk pistons. Resulting side thrust causes the pistons. Resulting side thrust causes the piston to press against the cylinder wall,piston to press against the cylinder wall, first first on one side, then on the other. At the top of on one side, then on the other. At the top of stroke, when the gas pressure is greatest, stroke, when the gas pressure is greatest, side thrust is negligible (due to small side thrust is negligible (due to small connecting rod angle). So most of wear connecting rod angle). So most of wear takes place at the middle of stroke: making takes place at the middle of stroke: making piston skirt increases thrust-bearing area, piston skirt increases thrust-bearing area, and hence reduces wear. In medium and and hence reduces wear. In medium and small size engines, due to lower gas small size engines, due to lower gas pressure, units’ side pressure is so small pressure, units’ side pressure is so small that neither piston nor liner wears much. that neither piston nor liner wears much.

In crosshead engines, crosshead takes the side In crosshead engines, crosshead takes the side thrust, which will be high in large engines. thrust, which will be high in large engines. So, crosshead engines have the followingSo, crosshead engines have the following advantages: advantages:

Easier lubrication.Easier lubrication.Reduced liner wear.Reduced liner wear.Uniformly distributed clearance around piston.Uniformly distributed clearance around piston.Simpler piston construction because the Simpler piston construction because the

‘Gudgeon pin’ and its bearing are eliminated. ‘Gudgeon pin’ and its bearing are eliminated. However these advantages of cross head However these advantages of cross head

engines are offset by: engines are offset by: Greater complication.Greater complication.Added weight.Added weight.Added height.Added height.Careful adjustments. Careful adjustments.

According to method of Charging.According to method of Charging.

(a) (a) Natural aspirated Engine. Natural aspirated Engine.

The vacuum is created when the piston The vacuum is created when the piston moves away from the combustion space moves away from the combustion space draws in the fresh charge.draws in the fresh charge.

(b) (b) Supercharged Engine.Supercharged Engine.

The charge is admitted into the cylinder at a The charge is admitted into the cylinder at a higher than atmospheric pressure. This higher than atmospheric pressure. This high pressure is produced by a pump or high pressure is produced by a pump or blower or exhaust gas turbocharger. blower or exhaust gas turbocharger.

According to Speed. According to Speed.

Slow Speed EnginesSlow Speed Engines: 100 to 150 r.p.m.: 100 to 150 r.p.m.

Medium Speed Engines:Medium Speed Engines: 300 to 1000 300 to 1000 r.p.m.r.p.m.

High Speed Engines:High Speed Engines: More than 1000 More than 1000 r.p.m. r.p.m.

According to Bore/Stroke Ratio: According to Bore/Stroke Ratio: a) a) Square Engine:Square Engine:If bore/stroke is about one, crankshaft web If bore/stroke is about one, crankshaft web

dimensions become less compared to dimensions become less compared to journal and crankpin.journal and crankpin.

b) b) Over Square Engines Over Square Engines (Short Stroke) (Short Stroke) If bore/stroke > 1, web dimensions (less If bore/stroke > 1, web dimensions (less

height, more thickness) are such that webs height, more thickness) are such that webs will be weak. So generally over square will be weak. So generally over square engines are not used. engines are not used.

(c) (c) Long Stroke EnginesLong Stroke Engines. .

Generally, engines have stroke/bore >1. Generally, engines have stroke/bore >1. This gives crankshafts of good This gives crankshafts of good strength. Most common ratio is strength. Most common ratio is stroke/bore = 2. 0: 2.2. stroke/bore = 2. 0: 2.2.

(d) (d) Super-long Stroke Engines. Super-long Stroke Engines.

To have better propeller efficiency and To have better propeller efficiency and better combustion even with lower better combustion even with lower grade fuels, lower r.p.m. engines with grade fuels, lower r.p.m. engines with longer strokes are gaining popularity. longer strokes are gaining popularity. These engines have stroke/bore ratio These engines have stroke/bore ratio = 3. = 3.

The Diesel Engines find the following The Diesel Engines find the following application on board merchant ships. application on board merchant ships.

Main Propulsion.Main Propulsion.

Electric Power generation.Electric Power generation.

Emergency Pumps (e.g. fire pump).Emergency Pumps (e.g. fire pump).

Life Boat.Life Boat.

Emergency Generator.Emergency Generator.

Emergency Air Compressor Emergency Air Compressor

REASONS FOR WIDE USE OF DIESEL REASONS FOR WIDE USE OF DIESEL ENGINES IN MARINE POWER PLANTSENGINES IN MARINE POWER PLANTS. .

1. 1. Small fuel consumption: Small fuel consumption: Diesel Engine is one of the most efficient Diesel Engine is one of the most efficient

heat engines. Hence it gives more power heat engines. Hence it gives more power with less fuel. It is an engine of high with less fuel. It is an engine of high economy.economy.

2. 2. Cheap fuel: Cheap fuel: Diesel engine uses fuel costing very less as Diesel engine uses fuel costing very less as

compared to other engines. compared to other engines. 3. 3. Economy at light loads: Economy at light loads: Diesel Engine is not only efficient when it is Diesel Engine is not only efficient when it is

fully loaded, but also when it is partly fully loaded, but also when it is partly loaded. loaded.

4. 4. Greater Safety: Greater Safety: Diesel fuel is non-explosive and less flammable Diesel fuel is non-explosive and less flammable

at normal temperatures and pressures. It at normal temperatures and pressures. It requires special effort to make it start to requires special effort to make it start to burn. This feature makes it very attractive in burn. This feature makes it very attractive in the marine trade, because it would be much the marine trade, because it would be much safer carrying diesel oil on board ships. safer carrying diesel oil on board ships.

Diesel exhaust gases are less poisonous than Diesel exhaust gases are less poisonous than other engines, because they contain less other engines, because they contain less carbon monoxide. carbon monoxide.

5. 5. Ignition System is not required: Ignition System is not required: Diesel engines do not require battery or Diesel engines do not require battery or

magneto running them. magneto running them. 6. More power can be produced due to more 6. More power can be produced due to more

compression allowed. compression allowed. 7. Diesel Engine is more robust and stronger.7. Diesel Engine is more robust and stronger.

8. 8. Economy in small sizesEconomy in small sizes: : As great contrast to steam power plant, a As great contrast to steam power plant, a

small diesel engine has nearly as good an small diesel engine has nearly as good an economy as a large one. This makes it economy as a large one. This makes it possible to enlarge a diesel engine plant possible to enlarge a diesel engine plant with additional units as the load grows. At with additional units as the load grows. At all stages of growth, the efficiency is high. all stages of growth, the efficiency is high.

9. 9. Sustained economy in service: Sustained economy in service: Again in contrast to a steam power plant, Again in contrast to a steam power plant,

diesel efficiency falls off very little during diesel efficiency falls off very little during thousands of hours of use between thousands of hours of use between overhauls. overhauls.

10. 10. Lightness and compactness: Lightness and compactness: Diesel engine plants have less weight and Diesel engine plants have less weight and

space per unit power. It is therefore well space per unit power. It is therefore well suited to portable and mobile installations. suited to portable and mobile installations.

11. 11. Independence of water supply: Independence of water supply: A diesel engine requires very less water A diesel engine requires very less water

in contrast to steam plants. in contrast to steam plants. 12. 12. Quick Starting. Quick Starting. A cold diesel engine can be started A cold diesel engine can be started

instantly and made to carry its full load instantly and made to carry its full load in few minutes. It is therefore ideal for in few minutes. It is therefore ideal for supplying emergency power. supplying emergency power.

13. 13. Easily in Maneuvering: Easily in Maneuvering: A diesel engine can be made to run at A diesel engine can be made to run at

full power in either direction. full power in either direction. 14.14. Economy in Labour. Economy in Labour. NoNo fire room force is needed. fire room force is needed.

15. 15. Freedom from nuisance: Freedom from nuisance: There are no ashes to be disposed of, no There are no ashes to be disposed of, no

noisy and dusty coal handling and noisy and dusty coal handling and pulverising equipment to maintain, no pulverising equipment to maintain, no smoke, and noise can be easily eliminated. smoke, and noise can be easily eliminated. Due to above mentioned reasons, Diesel Due to above mentioned reasons, Diesel engines are quite popular on board ships. engines are quite popular on board ships.

These reasons can very well be regarded as These reasons can very well be regarded as the advantages of Diesel Engines over the advantages of Diesel Engines over other prime movers such as gasoline other prime movers such as gasoline engines, gas turbines, steam engines, engines, gas turbines, steam engines, steam turbines and hydraulic turbines. steam turbines and hydraulic turbines.

However, Diesel engines also have However, Diesel engines also have certain disadvantages, which can be certain disadvantages, which can be listed as followinglisted as following: :

1. 1. Cost: Cost: Diesel engines, because of the higher pressures Diesel engines, because of the higher pressures

at which, they work, require sturdier at which, they work, require sturdier construction, better materials and closer fits construction, better materials and closer fits than gasoline engines. Therefore, they cost than gasoline engines. Therefore, they cost more to build. more to build.

2. Weight: 2. Weight: Because of sturdier construction, weight per Because of sturdier construction, weight per

power is more than gasoline engines. power is more than gasoline engines. 3. 3. Attendance: Attendance: A diesel engine requires more attention than an A diesel engine requires more attention than an

electric motor running on purchased current. electric motor running on purchased current. It also requires more attention per unit of It also requires more attention per unit of power produced than a large steam turbine. power produced than a large steam turbine.

4. 4. Fuel Cost: Fuel Cost: Oil used in Diesel engines is costlier than coal. Oil used in Diesel engines is costlier than coal.

Hence, steam power plants using coal as fuel Hence, steam power plants using coal as fuel are cheaper in operation. are cheaper in operation.

According to Operating Cycles.According to Operating Cycles.

(a) (a) OTTO CYCLE (Constant Volume OTTO CYCLE (Constant Volume Combustion CycleCombustion Cycle). ).

It is the ideal air standard cycle for Petrol It is the ideal air standard cycle for Petrol engine, the gas engine and the high-speed engine, the gas engine and the high-speed oil engine. The engines based on this cycle oil engine. The engines based on this cycle have high thermal efficiency but noisiness have high thermal efficiency but noisiness results particularly at higher power due to results particularly at higher power due to higher pressures in the cylinders. higher pressures in the cylinders.

Otto cycleOtto cycle

T = temperatureS = Entropy

Constant volume cycle

1-2 isentropic compression

2-3 heat addition at constant volume

3-4 isentropic expansion

4-1 heat rejection at constant volume

Air standard thermal efficiency = 1-(1/r) , r = comp. Ratio.

(b) (b) DIESEL CYCLE (Constant Pressure DIESEL CYCLE (Constant Pressure Combustion Cycle).Combustion Cycle).

It is the ideal Air standard cycle for Diesel It is the ideal Air standard cycle for Diesel Engine, especially suitable for low speed Engine, especially suitable for low speed Diesel Engine but not for high speed Diesel Diesel Engine but not for high speed Diesel Engine. (The thermal efficiency is lower Engine. (The thermal efficiency is lower than Otto cycle engines but engines run than Otto cycle engines but engines run smoothly due to lower pressures in the smoothly due to lower pressures in the cylinder. cylinder.

(c) (c) DUAL COMBUSTION CYCLE (Constant DUAL COMBUSTION CYCLE (Constant Pressure and Constant Volume Combustion Pressure and Constant Volume Combustion Cycle).Cycle).

Modern Diesel Engines do not operate purely Modern Diesel Engines do not operate purely on constant pressure combustion cycle but on constant pressure combustion cycle but some part of combustion process takes some part of combustion process takes place at constant volume while the rest is place at constant volume while the rest is completed at constant pressure. completed at constant pressure.

In general, this cycle resembles Constant In general, this cycle resembles Constant volume combustion Cycle more than volume combustion Cycle more than constant pressure combustion cycle. It is constant pressure combustion cycle. It is suitable for modern Medium and High suitable for modern Medium and High Speed Diesel Engines. The thermal Speed Diesel Engines. The thermal efficiency is more than Diesel Cycle but less efficiency is more than Diesel Cycle but less than Otto cycle. Also noise level is in than Otto cycle. Also noise level is in between the two. This is a more practical between the two. This is a more practical engine. engine.

Dual combustionDual combustion

Mixed cycle of otto and diesel cycle

Heat added partly at constant volume and partly at constant pressure.

hence having advantages of both cycles.

According to Strokes/Cycle.According to Strokes/Cycle.In an engine, the following events form a cycle: In an engine, the following events form a cycle: Filling the engine cylinder with fresh air. Filling the engine cylinder with fresh air. Compressing the air so much that injected fuel ignited Compressing the air so much that injected fuel ignited

readily by coming in contact with hot air and burns readily by coming in contact with hot air and burns efficiently.efficiently.

Combustion of fuel.Combustion of fuel.Expansion of hot gases.Expansion of hot gases.Emptying the products of combustion from the cylinder. Emptying the products of combustion from the cylinder. Depending on how many strokes of piston are required Depending on how many strokes of piston are required

in completing this cycle, the engines can be divided in completing this cycle, the engines can be divided into two classes: into two classes:

1. 1. Four Stroke Engine Four Stroke Engine An engine, which needs 4 strokes of the piston (2 in An engine, which needs 4 strokes of the piston (2 in

and 2 out) to complete one cycle, is called Four-and 2 out) to complete one cycle, is called Four-stroke engine. stroke engine.

2. 2. Two Stroke Engine Two Stroke Engine An engine that needs only 2 strokes of the piston (1 in An engine that needs only 2 strokes of the piston (1 in

and 1 out) to complete one cycle is called Two-stroke and 1 out) to complete one cycle is called Two-stroke engine. engine.

According to Piston Connection. According to Piston Connection.

Trunk Piston TypeTrunk Piston Type..

The piston is connected directly to the upper The piston is connected directly to the upper end of the connecting rod. A horizontal pin end of the connecting rod. A horizontal pin (Gudgeon Pin) within piston is encircled by (Gudgeon Pin) within piston is encircled by the upper end of the connecting rod. This the upper end of the connecting rod. This construction is quite common, especially construction is quite common, especially in small and medium size engines. in small and medium size engines.

(b) (b) Cross Head TypeCross Head Type. . The piston fastens to a vertical piston The piston fastens to a vertical piston

rod whose lower end is attached to a rod whose lower end is attached to a ‘cross head’, which slides up and ‘cross head’, which slides up and down in guides. The crosshead down in guides. The crosshead carries a crosshead pin, which is carries a crosshead pin, which is encircled by the upper end of the encircled by the upper end of the connecting rod. This more connecting rod. This more complicated construction is common complicated construction is common in double acting engines and large in double acting engines and large slow speed single acting engines. slow speed single acting engines.

Comparison between Trunks Piston Comparison between Trunks Piston Versus Cross Head EngineVersus Cross Head Engine. .

Most medium and small size engines use trunk Most medium and small size engines use trunk pistons. Resulting side thrust causes the pistons. Resulting side thrust causes the piston to press against the cylinder wall,piston to press against the cylinder wall, first first on one side, then on the other. At the top of on one side, then on the other. At the top of stroke, when the gas pressure is greatest, stroke, when the gas pressure is greatest, side thrust is negligible (due to small side thrust is negligible (due to small connecting rod angle). So most of wear connecting rod angle). So most of wear takes place at the middle of stroke: making takes place at the middle of stroke: making piston skirt increases thrust-bearing area, piston skirt increases thrust-bearing area, and hence reduces wear. In medium and and hence reduces wear. In medium and small size engines, due to lower gas small size engines, due to lower gas pressure, units’ side pressure is so small pressure, units’ side pressure is so small that neither piston nor liner wears much. that neither piston nor liner wears much.

In crosshead engines, crosshead takes the side In crosshead engines, crosshead takes the side thrust, which will be high in large engines. thrust, which will be high in large engines. So, crosshead engines have the followingSo, crosshead engines have the following advantages: advantages:

Easier lubrication.Easier lubrication.Reduced liner wear.Reduced liner wear.Uniformly distributed clearance around piston.Uniformly distributed clearance around piston.Simpler piston construction because the Simpler piston construction because the

‘Gudgeon pin’ and its bearing are eliminated. ‘Gudgeon pin’ and its bearing are eliminated. However these advantages of cross head However these advantages of cross head

engines are offset by: engines are offset by: Greater complication.Greater complication.Added weight.Added weight.Added height.Added height.Careful adjustments. Careful adjustments.

According to method of Charging.According to method of Charging.

(a) (a) Natural aspirated Engine. Natural aspirated Engine.

The vacuum is created when the piston The vacuum is created when the piston moves away from the combustion space moves away from the combustion space draws in the fresh charge.draws in the fresh charge.

(b) (b) Supercharged Engine.Supercharged Engine.

The charge is admitted into the cylinder at a The charge is admitted into the cylinder at a higher than atmospheric pressure. This higher than atmospheric pressure. This high pressure is produced by a pump or high pressure is produced by a pump or blower or exhaust gas turbocharger. blower or exhaust gas turbocharger.

According to Speed. According to Speed.

Slow Speed EnginesSlow Speed Engines: 100 to 150 r.p.m.: 100 to 150 r.p.m.

Medium Speed Engines:Medium Speed Engines: 300 to 1000 300 to 1000 r.p.m.r.p.m.

High Speed Engines:High Speed Engines: More than 1000 More than 1000 r.p.m. r.p.m.

According to Bore/Stroke Ratio: According to Bore/Stroke Ratio: a) a) Square Engine:Square Engine:If bore/stroke is about one, crankshaft web If bore/stroke is about one, crankshaft web

dimensions become less compared to dimensions become less compared to journal and crankpin.journal and crankpin.

b) b) Over Square Engines Over Square Engines (Short Stroke) (Short Stroke) If bore/stroke > 1, web dimensions (less If bore/stroke > 1, web dimensions (less

height, more thickness) are such that webs height, more thickness) are such that webs will be weak. So generally over square will be weak. So generally over square engines are not used. engines are not used.

(c) (c) Long Stroke EnginesLong Stroke Engines. .

Generally, engines have stroke/bore >1. Generally, engines have stroke/bore >1. This gives crankshafts of good This gives crankshafts of good strength. Most common ratio is strength. Most common ratio is stroke/bore = 2. 0: 2.2. stroke/bore = 2. 0: 2.2.

(d) (d) Super-long Stroke Engines. Super-long Stroke Engines.

To have better propeller efficiency and To have better propeller efficiency and better combustion even with lower better combustion even with lower grade fuels, lower r.p.m. engines with grade fuels, lower r.p.m. engines with longer strokes are gaining popularity. longer strokes are gaining popularity. These engines have stroke/bore ratio These engines have stroke/bore ratio = 3. = 3.

The Diesel Engines find the following The Diesel Engines find the following application on board merchant ships. application on board merchant ships.

Main Propulsion.Main Propulsion.

Electric Power generation.Electric Power generation.

Emergency Pumps (e.g. fire pump).Emergency Pumps (e.g. fire pump).

Life Boat.Life Boat.

Emergency Generator.Emergency Generator.

Emergency Air Compressor Emergency Air Compressor

REASONS FOR WIDE USE OF DIESEL REASONS FOR WIDE USE OF DIESEL ENGINES IN MARINE POWER PLANTSENGINES IN MARINE POWER PLANTS. .

1. 1. Small fuel consumption: Small fuel consumption: Diesel Engine is one of the most efficient Diesel Engine is one of the most efficient

heat engines. Hence it gives more power heat engines. Hence it gives more power with less fuel. It is an engine of high with less fuel. It is an engine of high economy.economy.

2. 2. Cheap fuel: Cheap fuel: Diesel engine uses fuel costing very less as Diesel engine uses fuel costing very less as

compared to other engines. compared to other engines. 3. 3. Economy at light loads: Economy at light loads: Diesel Engine is not only efficient when it is Diesel Engine is not only efficient when it is

fully loaded, but also when it is partly fully loaded, but also when it is partly loaded. loaded.

4. 4. Greater Safety: Greater Safety: Diesel fuel is non-explosive and less flammable Diesel fuel is non-explosive and less flammable

at normal temperatures and pressures. It at normal temperatures and pressures. It requires special effort to make it start to requires special effort to make it start to burn. This feature makes it very attractive in burn. This feature makes it very attractive in the marine trade, because it would be much the marine trade, because it would be much safer carrying diesel oil on board ships. safer carrying diesel oil on board ships.

Diesel exhaust gases are less poisonous than Diesel exhaust gases are less poisonous than other engines, because they contain less other engines, because they contain less carbon monoxide. carbon monoxide.

5. 5. Ignition System is not required: Ignition System is not required: Diesel engines do not require battery or Diesel engines do not require battery or

magneto running them. magneto running them. 6. More power can be produced due to more 6. More power can be produced due to more

compression allowed. compression allowed. 7. Diesel Engine is more robust and stronger.7. Diesel Engine is more robust and stronger.

8. 8. Economy in small sizesEconomy in small sizes: : As great contrast to steam power plant, a As great contrast to steam power plant, a

small diesel engine has nearly as good an small diesel engine has nearly as good an economy as a large one. This makes it economy as a large one. This makes it possible to enlarge a diesel engine plant possible to enlarge a diesel engine plant with additional units as the load grows. At with additional units as the load grows. At all stages of growth, the efficiency is high. all stages of growth, the efficiency is high.

9. 9. Sustained economy in service: Sustained economy in service: Again in contrast to a steam power plant, Again in contrast to a steam power plant,

diesel efficiency falls off very little during diesel efficiency falls off very little during thousands of hours of use between thousands of hours of use between overhauls. overhauls.

10. 10. Lightness and compactness: Lightness and compactness: Diesel engine plants have less weight and Diesel engine plants have less weight and

space per unit power. It is therefore well space per unit power. It is therefore well suited to portable and mobile installations. suited to portable and mobile installations.

11. 11. Independence of water supply: Independence of water supply: A diesel engine requires very less water A diesel engine requires very less water

in contrast to steam plants. in contrast to steam plants. 12. 12. Quick Starting. Quick Starting. A cold diesel engine can be started A cold diesel engine can be started

instantly and made to carry its full load instantly and made to carry its full load in few minutes. It is therefore ideal for in few minutes. It is therefore ideal for supplying emergency power. supplying emergency power.

13. 13. Easily in Maneuvering: Easily in Maneuvering: A diesel engine can be made to run at A diesel engine can be made to run at

full power in either direction. full power in either direction. 14.14. Economy in Labour. Economy in Labour. NoNo fire room force is needed. fire room force is needed.

15. 15. Freedom from nuisance: Freedom from nuisance: There are no ashes to be disposed of, no There are no ashes to be disposed of, no

noisy and dusty coal handling and noisy and dusty coal handling and pulverising equipment to maintain, no pulverising equipment to maintain, no smoke, and noise can be easily eliminated. smoke, and noise can be easily eliminated. Due to above mentioned reasons, Diesel Due to above mentioned reasons, Diesel engines are quite popular on board ships. engines are quite popular on board ships.

These reasons can very well be regarded as These reasons can very well be regarded as the advantages of Diesel Engines over the advantages of Diesel Engines over other prime movers such as gasoline other prime movers such as gasoline engines, gas turbines, steam engines, engines, gas turbines, steam engines, steam turbines and hydraulic turbines. steam turbines and hydraulic turbines.

However, Diesel engines also have However, Diesel engines also have certain disadvantages, which can be certain disadvantages, which can be listed as followinglisted as following: :

1. 1. Cost: Cost: Diesel engines, because of the higher pressures Diesel engines, because of the higher pressures

at which, they work, require sturdier at which, they work, require sturdier construction, better materials and closer fits construction, better materials and closer fits than gasoline engines. Therefore, they cost than gasoline engines. Therefore, they cost more to build. more to build.

2. Weight: 2. Weight: Because of sturdier construction, weight per Because of sturdier construction, weight per

power is more than gasoline engines. power is more than gasoline engines. 3. 3. Attendance: Attendance: A diesel engine requires more attention than an A diesel engine requires more attention than an

electric motor running on purchased current. electric motor running on purchased current. It also requires more attention per unit of It also requires more attention per unit of power produced than a large steam turbine. power produced than a large steam turbine.

4. 4. Fuel Cost: Fuel Cost: Oil used in Diesel engines is costlier than coal. Oil used in Diesel engines is costlier than coal.

Hence, steam power plants using coal as fuel Hence, steam power plants using coal as fuel are cheaper in operation. are cheaper in operation.