Motors & Engines Transparency
Motors & Engines Transparency
Motors & Engines Transparency
(Review)
Engines convert the heat energy of fuel into mechanical energy by burning it and
allowing the burning gas to expand to produce mechanical power.
Mechanical power is manifested by the rotation and torque of the output shaft as:
Electric motors are more efficient in converting input energy into mechanical
energy compared to gasoline and diesel engines.
Despite the low conversion efficiency, engines are still considered one of the few
inventions that have great influence on human lives.
Electric motors are used as prime movers for stationary and indoor equipment such
as dryers, rice mills, conveyors and size reduction equipment.
Engines are used as prime movers for mobile and outdoor machinery such as
tractors, water pumps, sprayers, harvesters, threshers and shellers.
Engines are also used in fishing boats to increase the mobility of fishermen and the
scope of their fishing grounds.
In general, engines are used in applications where electric motors cannot be used.
Electric Motors
1. Torque requirement:
Select a motor whose torque output is always greater than the torque required
by the load.
Determines the size and capacities of the electrical installations needed to operate
the motor (transformer capacity, wire size, breaker capacity, switch rating)
For example, calculate the maximum locked-rotor current (starting current) for a
½-hp, 220-volt motor with an H motor code.
3. Temperature rating:
Motors are built with four insulation classes that can withstand only certain
amounts of operating temperature.
For convenience, nameplate data often gives the maximum ambient temperature
that will keep the motor temperature within limits. Normal maximum ambient
temperature for motor operation is 40 ºC
4. Duty rating:
5. Enclosure:
Motors are classified according to the type of enclosure used to protect the motor
from the environment:
b. Closed-type – does not allow entry of air inside the motor. Fan blows
air on the outside surface of the frame to dissipate heat. Fins are
constructed on the frame to increase the surface area for heat
dissipation.
6. Service factor – indicates the maximum load that can be safely carried by
the motor under continuous operation.
The service factor is multiplied by the horsepower rating to give the maximum
load the motor can sustain.
Motor nameplate:
Motor nameplate carries a good deal of essential information about the motor. Refer
to it when you specify, buy, install, replace, operate and repair motors.
Engines
Classification of engines:
TDC (top dead center) – highest position attained by the piston when
it goes up.
BDC (bottom dead center) – lowest position attained by the piston
when it goes down.
Stroke – movement of the piston from TDC to BDC or vice versa.
2) Upward stroke – as the piston goes up, both the inlet and
exhaust ports will be covered to start the compression event.
Engine specifications:
CHARACTERISTIC SPECIFICATION
Engine type : 4-stroke spark-ignition vertical single cylinder
Maximum output : 6.8 hp at 4,000 rpm
Rated output : 5.0 hp at 3,600 rpm
Bore x stroke, displacement : 72 x 59 mm, 240 cc
Compression ratio : 6:1
Maximum torque : 1.25 kg-m at 3,000 rpm
Ignition system : flywheel magneto
Starting system : recoil starter
Air cleaner : semi-dry type (polyurethane)
Lubrication system : splash type
Lubrication capacity : 0.82 li
Fuel tank capacity : 6.9 li
Dry weight : 28 kg
Dimensions : 410 mm x 370 mm x 490 mm
Basic engine terminology:
2. Stroke (L) – length of travel of the piston from TDC to BDC, inches or
millimeters
5. Total Volume (TV) – volume of the cylinder when the piston is at BDC. It
is equal to PD + CV.
Sample problem 1:
Determine the compression ratio of the engine with the following specifications:
Total volume = 70 cc, Bore = 4 cm and Stroke = 5 cm.
Required: Find CR
Solution:
Sample problem 2:
Determine the bore of the engine if its clearance volume is 7.18 cc, compression
ratio is 8:1 and stroke is 4 cm.
Required: Bore = D
Solution:
= = =
Figure 3. Operation of 4-stroke spark ignition engine
Reading Assignment: