7.1 Define swept volume in an internal combustion engine - NSC Mechanical Technology Automotive - Question 7 - 2019 - Paper 1
Question 7
7.1 Define swept volume in an internal combustion engine.
7.2 State THREE methods that can be used to increase the compression ratio of an internal combustion engin... show full transcript
Worked Solution & Example Answer:7.1 Define swept volume in an internal combustion engine - NSC Mechanical Technology Automotive - Question 7 - 2019 - Paper 1
Step 1
Define swept volume in an internal combustion engine.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The swept volume of an internal combustion engine is defined as the volume displaced by the piston as it moves from the bottom dead center (BDC) to the top dead center (TDC). This volume is crucial as it directly influences the engine's power output and efficiency.
Step 2
State THREE methods that can be used to increase the compression ratio of an internal combustion engine.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Remove shims between the cylinder block and cylinder head to decrease the clearance volume.
Thinner cylinder head gasket can be utilized to reduce the height of the cylinder head.
Fit a piston with a higher crown to increase the swept volume.
Step 3
The swept volume of a single cylinder in cm³.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The swept volume (SV) can be calculated using the formula:
\pi D^2}{4} imes L $$
where D is the bore diameter (90 mm) and L is the stroke length (100 mm). Thus,
$$ SV = rac{
\ imes(90)^2}{4} imes 100 = 636,17 ext{ cm}^3 $$
Step 4
The original clearance volume of a single cylinder in cm³.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The clearance volume (CV) can be calculated using the formula:
CV = rac{SV}{CR - 1}
where CR is the compression ratio (10.5). Thus,
CV = rac{636.17}{10.5 - 1} = 66,97 ext{ cm}^3
Step 5
The compression ratio is increased to 11 : 1. What will the new bore diameter be if the clearance volume remains unchanged? Answer in mm.
97%
117 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
To find the new bore diameter (D) when the compression ratio (CR) becomes 11, we use the formula for the new compression ratio:
CR = rac{SV + CV}{CV}
Substituting the known values:
11 = rac{SV + 66.97}{66.97}
Solving for SV gives:
SV=66.97imes(11−1)=669.7extcm3
Using the swept volume formula:
\ imes D^2}{4} imes L $$
Substituting known values:
$$ 669.7 = rac{
\ imes D^2}{4} imes 100 $$
Solving for D gives:
$$ D^2 = rac{669.7 imes 4}{
\ imes 100} $$
D = rac{669.7}{
\ imes 10} = 92,34 ext{ mm} $$
Step 6
Indicated power in kW.
97%
121 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The indicated power (IP) can be calculated using the formula:
IP=PimesLimesAimesNimesn
Where:
P = Mean effective pressure = 1300 kPa
L = Stroke length = 160 mm = 0.16 m
A =
\ imes D^2}{4} = rac{
\ imes (120)^2}{4} = 0.0113 ext{ m}^2 $$
- N = Engine speed in rpm = 4500
- n = Number of cylinders = 4
Substituting values, we find:
$$ IP = (1300 imes 10^3) imes 0.16 imes 0.0113 imes 37.5 imes 4 = 352.56 ext{ kW} $$
Step 7
Brake power in kW.
96%
114 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The brake power (BP) can be calculated using the formula:
BP=2extπimesNimesT
Where:
N = Engine speed in RPM = 4500
T = Torque = 610 Nm
Thus,
BP = 2 ext{π} imes rac{610}{60} imes 4500 = 28745.73 ext{ W}
Converting to kW:
BP=28.75extkW
Step 8
Mechanical efficiency of the engine.
99%
104 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
The mechanical efficiency can be calculated using the formula:
ext{Mechanical Efficiency} = rac{BP}{IP} imes 100
Substituting values, we get:
Define mechanical efficiency of an internal combustion engine.
96%
101 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Mechanical efficiency in an internal combustion engine is defined as the ratio of the brake power delivered by the engine to the indicated power developed within the engine. It reflects the effectiveness of the engine in converting the generated power into useful work.
Step 10
Define brake power of an internal combustion engine.
98%
120 rated
Only available for registered users.
Sign up now to view full answer, or log in if you already have an account!
Answer
Brake power is the actual power that an engine produces and is measured at the output shaft. It is the useful work done by the engine, minus losses from friction and heat dissipation. The brake power gives a clear indication of the engine's real performance.
