7.1 Define the term indicated power of an internal combustion engine - NSC Mechanical Technology Automotive - Question 7 - 2020 - Paper 1
Question 7
7.1 Define the term indicated power of an internal combustion engine.
7.2 State TWO methods to lower the compression ratio of an internal combustion engine.
7.3 Na... show full transcript
Worked Solution & Example Answer:7.1 Define the term indicated power of an internal combustion engine - NSC Mechanical Technology Automotive - Question 7 - 2020 - Paper 1
Step 1
Define the term indicated power of an internal combustion engine.
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Answer
Indicated power is the theoretical power that can be generated by an internal combustion engine without accounting for mechanical or other losses. It reflects the power produced by burning fuel within the engine's cylinders.
Step 2
State TWO methods to lower the compression ratio of an internal combustion engine.
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Answer
Fit a piston with suitable lower crowns.
Use a thicker gasket between the cylinder block and cylinder head.
Step 3
Name TWO types of dynamometers used to measure the power output of a motor vehicle.
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Electric dynamometer.
Water-brake (hydraulic) dynamometer.
Step 4
Determine, by means of calculations:
7.4.1 The swept volume of a single cylinder in cm³.
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Answer
The swept volume (SV) of a single cylinder can be calculated using the formula:
u D^2}{4} imes L$$
Where:
- $
u = ext{π}$
- $D = 70 mm = 0.07 m$
- $L = 90 mm = 0.09 m$
Calculating, we get:
$$SV = rac{π (0.07 m)^2}{4} imes 0.09 m \
= 0.346 cm³$$
Step 5
Determine, by means of calculations:
7.4.2 The original clearance volume of a single cylinder in cm³.
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Answer
To find the clearance volume (CV), we can use the compression ratio (CR).
Determine, by means of calculations:
7.4.3 What will be the new diameter of the bore if the clearance volume remains unchanged?
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Answer
Given the new compression ratio (CR) is 9.5 : 1, we can rearrange the formula.
First, calculate the new swept volume (SV):
= 53.29 imes (9.5 - 1) = 452.965 cm³$$
2. Now use the swept volume to find the new bore diameter (D):
$$SV = rac{
u D^2}{4} imes L\
D^2 = rac{SV imes 4}{
u L}\
= rac{452.965 imes 4}{π imes 0.09}\
D = ext{Calculate D from above} = 80.05 mm$$
Step 7
Determine, by means of calculations:
7.5.1 Torque.
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Answer
The torque (T) can be calculated using:
extTorque=extMassimesextGravityimesextDistance
Substituting in the known values:
T=50imes10imes1=500Nimesm
Step 8
Determine, by means of calculations:
7.5.2 Brake power in kW.
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Answer
Brake power (BP) can be calculated using:
BP=2πnT
Where:
n=4500/60=75 revs/second
Thus:
BP=2πimes75imes500=235.619kW
Step 9
Determine, by means of calculations:
7.5.3 Indicated power in kW.
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Answer
Indicated power (IP) can be computed using:
IP=PimesLimesAimesn
Where:
P=1450kPa,
L=0.14m,
A = rac{π D^2}{4}, with D=0.11m,
n = rac{4500}{60 imes 2} = 37.5 extrm{ cycles/second}.
Thus, you can substitute to find IP:
IP=1450imes0.14imesAimesn=289.278kW
Step 10
Determine, by means of calculations:
7.5.4 Mechanical efficiency.
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Answer
Mechanical efficiency can be calculated using:
ext{Efficiency} = rac{BP}{IP} imes 100
Substituting:
ext{Efficiency} = rac{235.62}{289.278} imes 100 = 81.45\%
