Questions and Answers
What is the primary function of an engine?
Which type of engine is a steam engine?
What is the purpose of a piston ring?
What is the classification of a tractor with both wheels and tracks?
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What is the term for the distance the piston travels in one direction?
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What is the ratio of cylinder volume to clearance volume?
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What is the purpose of the crankcase?
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What is the application of internal combustion engines in agriculture?
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What is engine efficiency a measure of?
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How many events take place inside the combustion chamber in the operation of internal combustion engines?
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What is the formula to calculate the efficiency of an ideal Otto cycle?
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Which type of engine gives a higher theoretical efficiency?
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Why is the compression ratio of Otto-cycle engine limited?
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How many movements of the piston are required to complete the cycle in a two-stroke cycle engine?
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Which type of engine typically uses higher compression pressures than Otto-cycle engine?
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How many power strokes are there in a four-stroke cycle engine per two revolutions of the crankshaft?
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What is the characteristic of the valve mechanism in a small engine?
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What is the fuel consumption of a large engine compared to a small engine?
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How does the stability of rpm vary with the size of the flywheel?
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How does the lubrication system work in a small engine?
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What is the characteristic of oil consumption in a small engine?
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What is the characteristic of the self-weight and size of a small engine?
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Study Notes
Heat Engines
- Heat engines are mechanical devices that convert heat energy of fuels into mechanical energy.
- External combustion engines (ECE) ignite and burn fuel outside a cylinder, and the heat energy is applied indirectly to a piston by an intermediate medium, usually water vapor.
- Steam engines are an example of external combustion engines.
- Internal combustion engines (ICE) ignite and burn fuel inside a cylinder, and the resulting explosion causes an instantaneous application of pressure to a piston.
Applications of Internal Combustion Engines
- Used as stationary power sources for milling, grinding, water pumping, generation of electricity, etc.
- Used as power units of portable farm equipment such as sprayers, threshers, and self-propelled machines such as tractors, combines, and harvesters.
Classification of Tractors
- 2-wheel tractor (hand tractor)
- Compact 4-wheel tractor
- Combination wheel type and track type
- Tract type or crawler
- Combination wheel type and tract type
Main Engine Components
- Cylinder
- Piston rings
- Cylinder block
- Piston pin
- Cylinder head
- Valves
- Crankcase
- Piston
- Intake manifold
- Exhaust manifold
- Connecting rod
- Crankshaft
- Flywheel
Physical Nomenclature
- Bore (d): the diameter of the engine cylinder
- Stroke (l): distance the piston travels in one direction
- Piston displacement (Pd): volume displaced by the piston in one stroke
- Clearance volume (Cv): the space inside the cylinder when the piston is at top dead center position
- Cylinder volume: the sum of piston displacement and clearance volume (Pd + Cv)
- Compression ratio (Cr): ratio of cylinder volume to clearance volume
- Engine efficiency: a measure of the ability of an engine to convert fuel into useful work
Engine Cycles and Principles of Operation
- Four events repeatedly take place inside the combustion chamber in a definite order: intake, compression, power, and exhaust.
- Classification of engines: 4-stroke cycle and 2-stroke cycle engines.
Comparison of 4-stroke Cycle and 2-stroke Cycle Engines
- 4-stroke cycle engines require four movements of the piston to complete the cycle.
- 2-stroke cycle engines require two movements of the piston to complete the cycle.
- 4-stroke cycle engines have smaller power, require valve mechanism, have complicated construction, consume less fuel, and have good durability.
- 2-stroke cycle engines have larger power, do not require valve mechanism, have simple construction, consume more fuel, and have good durability.
Types of Engines
- Four-stroke cycle spark ignition engine
- Four-stroke cycle compression ignition engine
- Two-stroke cycle spark ignition engine
- Two-stroke cycle compression ignition engine
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Description
Learn about the difference between external and internal combustion engines, and how they convert heat energy into mechanical energy.