SOLVED PROBLEMS OF CHAPTER # 13
TITLE: RECPROCTING INTERNAL COMBUSTION ENGINES
PROBLEM # 13.1:
A quantity governed four-stroke, single-cylinder gas engine has a bore of 146mm and a stroke of 280mm.At 475 rev/min and full load the net load on the friction brake is 433 N, and the torque arm is 0.45 m. The indicator diagram gives a net area of 578 mm² and a length of 70 mm with a spring rating of 0.815 bar per mm. calculate the ip,bp, and mechanical efficiency.
GIVEN DATA:
Four stroke single cylinder gas engine n = no. of cylinders = 1
Dia. of cylinder bore = 146 mm = 0.146 m
Length of stroke = L = 280 mm = 0.28 m
N = 475 revolution/min = 475/ 60 rev/sec. = 7.5416 rev/sec.
Full load, break load = W = B = 433 N
Torque
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Calculate the maximum bmep,the maximum bp,the minimum specific fuel consumption, and the maximum brake thermal efficiency at maximum torque and compare this latter answer with the air standard efficiency.
GIVEN DATA: Four cylinder racing engine n = no of cylinder = 4 Capacity of cylinder = V = 2.495 liters = 0.002495 m3 Dia of the bore = b = 94 mm= 0.94 m Compression ratio= 12/1 = rv Tested by dynamometer gives = k = 0.461 m Wmax = 622N
N = 5000 rev/min = 83.3 rev/sec
Nmax = 6750/ 60 = 112. rev /sec
W = 547 N
Mini. Fuel consumption = 17.2 ml/s at 5000 rev/min
Specific gravity of the fuel = 0.735
Qnet,p = 44200 KJ/Kg
REQUIRED:
Max. bmep =? , (Pb) max. =?
Min. specific fuel consumption, (spc.)min. =?
(ηBT)max.= ? (At max. torque)
Compare this with the Air Standard Efficiency
SOLUTION:
As Tmax. = Wmax. * R = 622 * 0.461 = 286.74 Nm
At Tmax bp = 2πTmax. * N
(Sfc)min = mf / bp=0.012642 /150.13*103
=8.42*10-5 kg/kg = 8.42*10-5 *3600 kg/kg = 0.303
((BT)max = bp / mf*Qnet
=150.13*103/0.012642*44200*103 =. 2686 = 26.86 %
For Air Standard Efficiency, we have a relation,
( = 1-1/(rq)γ-1 = 1-1/120.4 = 0.63 = 63 %
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