8/2/2019 m 1.IV Diesel Engines Cycles http://slidepdf.com/reader/full/m-1iv-diesel-engines-cycles 1/49 According to Operating Cycles. (a) OTTO CYCLE (Constant Volume Combustion Cycle). It is the ideal air standard cycle for Petrol engine, the gas engine and the high-speed oil engine. The engines based on this cycle have high thermal efficiency but noisiness results particularly at higher power due to higher pressures in the cylinders.
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engine, the gas engine and the high-speed oilengine. The engines based on this cycle havehigh thermal efficiency but noisiness resultsparticularly at higher power due to higher
constant pressure combustion cycle but somepart of combustion process takes place atconstant volume while the rest is completed atconstant pressure.
In general, this cycle resembles Constant volumecombustion Cycle more than constant pressurecombustion cycle. It is suitable for modernMedium and High Speed Diesel Engines. The
thermal efficiency is more than Diesel Cycle butless than Otto cycle. Also noise level is inbetween the two. This is a more practicalengine.
The piston fastens to a vertical piston rodwhose lower end is attached to a ‘crosshead’, which slides up and down inguides. The crosshead carries a crosshead
pin, which is encircled by the upper end of the connecting rod. This more complicatedconstruction is common in double acting
engines and large slow speed single actingengines.
Comparison between Trunks Piston VersusCross Head Engine.
Most medium and small size engines use trunk pistons. Resulting side thrust causes the piston topress against the cylinder wall, first on one side,then on the other. At the top of stroke, when thegas pressure is greatest, side thrust is negligible
(due to small connecting rod angle). So most of wear takes place at the middle of stroke: makingpiston skirt increases thrust-bearing area, andhence reduces wear. In medium and small sizeengines, due to lower gas pressure, units’ side
pressure is so small that neither piston nor linerwears much.
4. Greater Safety:Diesel fuel is non-explosive and less flammable at
normal temperatures and pressures. It requires
special effort to make it start to burn. This featuremakes it very attractive in the marine trade,because it would be much safer carrying diesel oilon board ships.
Diesel exhaust gases are less poisonous than otherengines, because they contain less carbonmonoxide.
5. Ignition System is not required:Diesel engines do not require battery or magneto
running them.6. More power can be produced due to more
compression allowed.7. Diesel Engine is more robust and stronger.
8. Economy in small sizes: As great contrast to steam power plant, a small
diesel engine has nearly as good an economy as
a large one. This makes it possible to enlarge adiesel engine plant with additional units as theload grows. At all stages of growth, the efficiencyis high.
9. Sustained economy in service: Again in contrast to a steam power plant, dieselefficiency falls off very little during thousands of hours of use between overhauls.
10. Lightness and compactness:Diesel engine plants have less weight and space
per unit power. It is therefore well suited toportable and mobile installations.
15. Freedom from nuisance:There are no ashes to be disposed of, no noisy
and dusty coal handling and pulverisingequipment to maintain, no smoke, and noise canbe easily eliminated. Due to above mentionedreasons, Diesel engines are quite popular onboard ships.
These reasons can very well be regarded as theadvantages of Diesel Engines over other primemovers such as gasoline engines, gas turbines,steam engines, steam turbines and hydraulic
turbines.However, Diesel engines also have certaindisadvantages, which can be listed asfollowing:
1. Cost:Diesel engines, because of the higher pressures at
which, they work, require sturdier construction,
better materials and closer fits than gasolineengines. Therefore, they cost more to build.2. Weight:Because of sturdier construction, weight per power is
more than gasoline engines.3. Attendance: A diesel engine requires more attention than an
electric motor running on purchased current. It alsorequires more attention per unit of power producedthan a large steam turbine.
4. Fuel Cost:Oil used in Diesel engines is costlier than coal. Hence,
steam power plants using coal as fuel are cheaper in
Cycle).It is the ideal air standard cycle for Petrol engine,
the gas engine and the high-speed oil engine.The engines based on this cycle have highthermal efficiency but noisiness resultsparticularly at higher power due to higherpressures in the cylinders.
constant pressure combustion cycle but somepart of combustion process takes place atconstant volume while the rest is completed atconstant pressure.
In general, this cycle resembles Constant volumecombustion Cycle more than constant pressurecombustion cycle. It is suitable for modernMedium and High Speed Diesel Engines. Thethermal efficiency is more than Diesel Cycle butless than Otto cycle. Also noise level is inbetween the two. This is a more practicalengine.
of the connecting rod. A horizontal pin (GudgeonPin) within piston is encircled by the upper endof the connecting rod. This construction is quitecommon, especially in small and medium sizeengines.
Comparison between Trunks Piston VersusCross Head Engine.
Most medium and small size engines use trunk pistons. Resulting side thrust causes the piston topress against the cylinder wall, first on one side,then on the other. At the top of stroke, when thegas pressure is greatest, side thrust is negligible
(due to small connecting rod angle). So most of wear takes place at the middle of stroke: makingpiston skirt increases thrust-bearing area, andhence reduces wear. In medium and small sizeengines, due to lower gas pressure, units’ side
pressure is so small that neither piston nor linerwears much.
4. Greater Safety:Diesel fuel is non-explosive and less flammable at
normal temperatures and pressures. It requires
special effort to make it start to burn. This featuremakes it very attractive in the marine trade,because it would be much safer carrying diesel oilon board ships.
Diesel exhaust gases are less poisonous than otherengines, because they contain less carbonmonoxide.
5. Ignition System is not required:Diesel engines do not require battery or magneto
running them.6. More power can be produced due to more
compression allowed.7. Diesel Engine is more robust and stronger.
8. Economy in small sizes: As great contrast to steam power plant, a small
diesel engine has nearly as good an economy as
a large one. This makes it possible to enlarge adiesel engine plant with additional units as theload grows. At all stages of growth, the efficiencyis high.
9. Sustained economy in service: Again in contrast to a steam power plant, diesel
efficiency falls off very little during thousands of hours of use between overhauls.
10. Lightness and compactness:Diesel engine plants have less weight and space
per unit power. It is therefore well suited toportable and mobile installations.
15. Freedom from nuisance:There are no ashes to be disposed of, no noisy
and dusty coal handling and pulverisingequipment to maintain, no smoke, and noise canbe easily eliminated. Due to above mentionedreasons, Diesel engines are quite popular onboard ships.
These reasons can very well be regarded as theadvantages of Diesel Engines over other primemovers such as gasoline engines, gas turbines,steam engines, steam turbines and hydraulic
turbines.However, Diesel engines also have certaindisadvantages, which can be listed asfollowing:
1. Cost:Diesel engines, because of the higher pressures at
which, they work, require sturdier construction,
better materials and closer fits than gasolineengines. Therefore, they cost more to build.2. Weight:Because of sturdier construction, weight per power is
more than gasoline engines.3. Attendance:
A diesel engine requires more attention than anelectric motor running on purchased current. It alsorequires more attention per unit of power producedthan a large steam turbine.
4. Fuel Cost:Oil used in Diesel engines is costlier than coal. Hence,
steam power plants using coal as fuel are cheaper in