A four-stroke SI engine 0.08 m bore (d), 0.10 m stroke (L), is tested at full throttle at constant speed. The fuel supply is fixed at 0.0011333 kg/s and the spark plugs of the four cylinders are successively short circuited without change of speed, brake torque being correspondingly adjusted. The brake power (bp) measurements are the following: With all cylinders firing = 12.5 kW With cylinder No. 1 cut off = 9 kW With cylinder No. 2 cut off = 9.15 kW With cylinder No. 3 cut off = 9.2 kW With cylinder No. 2 cut off = 9.1 kW The lower calorific (or heating value, LCVf) of the fuel is 44100 kJ/kg. The clearance volume (Vcl) of one cylinder 70.0 x 103 mm3. Determine:
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A four-stroke SI engine 0.08 m bore (d), 0.10 m stroke (L), is tested at full throttle at constant speed. The fuel supply is fixed at 0.0011333 kg/s and the spark plugs of the four cylinders are successively short circuited without change of speed, brake torque being correspondingly adjusted. The brake power (bp) measurements are the following:
With all cylinders firing = 12.5 kW
With cylinder No. 1 cut off = 9 kW
With cylinder No. 2 cut off = 9.15 kW
With cylinder No. 3 cut off = 9.2 kW
With cylinder No. 2 cut off = 9.1 kW
The lower calorific (or heating value, LCVf) of the fuel is 44100 kJ/kg. The clearance
volume (Vcl) of one cylinder 70.0 x 103 mm3. Determine:
(a) Indicated power (ip) of the engine under these conditions.
(b) The indicated thermal efficiency
(c) The relative efficiency of this engine.
Given data
bore (d) = 0.08 m
stroke (L) = 0.10 m
fuel supply () = 0.0011333 kg/s
LCVf = 44100 kJ/kg
Vcl = 70*103 mm3
BPo = 12.5 kW
BP1 = 9 kW
BP2 = 9.15 kW
BP3 = 9.2 kW
BP4 = 9.1 kW
To determine
(a) Indicated power of the engine
(b) indicated thermal efficiency
(c) the relative efficiency of the engine
(a)from morse test
indicated power of cylinder 1 can be calculated as below
IP1 = BPo - BP1
= 12.5 kW - 9 kW
= 3.5 kW
similarly, Indicated power of cylinder 2 can be calculated as below
IP2 = BPo - BP2
= 12.5 kW - 9.15 kW
= 3.35 kW
IP3 = BPo - BP3
= 12.5 kW - 9.2 kW
= 3.3 kW
IP4 = BP0 - BP4
= 12.5 kW - 9.1 kW
= 3.4 kW
thus, total indicated power of the engine (IP) = IP1 + IP2 + IP3 + IP4
= 3.5 kW + 3.35 kW + 3.3 kW + 3.4 kW
= 13.55 kW
(b) The indicated thermal efficiency can be calculated as below
= 0.27112
(c) first, we need to calculate the swept volume/ displaced volume
= 5.026*10-4 m3
= 502.6*103 mm3
clearance volume (Vc) = 70*103 mm3
compression ratio (r) can be calculated as below
= 8.18
Now, air standard efficiency will be
= 0.5686
relative efficiency of an engine is the ratio of indicated thermal efficiency to air standard efficiency
= 0.4767
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