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The crank and connecting rod of a petrol engine, running at 1800 r.p.m. are 50 mm and 200 mm respectively. The diameter of the piston is 80 mm and the mass of the reciprocating parts is 1 kg. At a point during the power stroke, the pressure on the piston is 0.7 N/mm2, when it has moved 10 mm from the inner dead centre. Determine: 1. Net load on the gudgeon pin, 2. Thrust in the connecting rod, 3. Reaction between the piston and cylinder, and 4. The engine speed at which the above values become zero. |
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Answer» Given : N = 1800 r.p.m. or ω = 2π x 1800/60 = 1888.52 rad/s; r = 50 mm = 0.05 m; l = 200mm; D = 80 mm; mR = 1 kg; P = 0.7 N/mm2; x = 10 mm 1. Net load on the gudgeon pin We know that load on the piston When the piston has moved 10 mm from the inner dead centre i.e when P1P = 10 mm the crank rotates from OC1 to OC through an angle θ By measurement we find that θ = 33°.We know that ratio of lengths of connecting rod and crank n = l/r = 200/50 = 4and inertia force on the reciprocating parts We know that net load on the gudgeon pin FP = FL - F = 3520 - 1671 = 1849 N 2. Thrust in the connecting rod We know that thrust in the connecting rod 3. The reaction between the piston and cylinder We know that reaction between the piston and cylinder 4. Engine speed at which the above values will become zero A little consideration will show that the above values will become zero if inertia force on the reciprocating parts F1 is equal to the load on the piston FL. Let ω1 be the speed in rad/s at which FI = FL |
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