Question

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 **, the pressure on the piston is 0.7 N/mm2, when it has moved 10 mm from the inner **** 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

Answer 1

Given : N = 1800 r.p.m. or ω = 2π x 1800/60 = 1888.52 rad/*; 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 **** 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 legths of connecting rod and crank,

n = l/r = 200/50 = 4

and 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. 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/*, at which FI = FL