A single-cylinder double-acting steam engine with 15 cm bore and 20 cm stroke is to develop 20 kW at 300 r.p.m. with cut-off occurring at 20% of stroke. Back pressure is 0.28 bar. Determine admission pressure if diagram factor is 0.72. Also calculate indicated thermal efficiency if engine receives

Question

A single-cylinder double-acting steam engine with 15 cm bore and 20 cm stroke is to develop 20 kW at 300 r.p.m. with cut-off occurring at 20% of stroke. Back pressure is 0.28 bar. Determine admission pressure if diagram factor is 0.72. Also calculate indicated thermal efficiency if engine receives 222 kg of dry steam per hour. Neglect area of piston rod. (AMIE)

Accepted Answer

Engine bore, D = 15 cm = 0.15 m
Stroke length, L = 20 cm = 0.2 m
Speed of the engine, N = 300 r.p.m.
Power developed, I.P. = 20 kW
Diagram factor, D.F. = 0.72
Steam (dry) supplied per hour = 222 kg/h
Cut-off ratio, [latex] \frac{V_{1}}{V_{2}} [/latex] = 0.2

Admission pressure, [latex]p_{1} [/latex] :

Indicated power, I.P. =[latex] \frac{p_{m} LAN × 10}{3} [/latex] kW [Eqn. (13)]

20 = [latex] \frac{p_{m} × 0.20 × \frac{π}{4} × 0.15² × 300 × 10}{3} = 3.534 p_{m} [/latex]

∴ [latex]p_{m} = \frac{20}{ 3.534} [/latex] = 5.659 bar

[latex]( p_{m)th.} = \frac{p_{m}}{D.F.} = \frac{5.659}{ 0.72}[/latex] = 7.86 bar

Also, [latex]( p_{m)th.} = \frac{p_{1}}{r} [1 + \log _{e} r ] - p_{ b}, [/latex]

where, r = (Expansion ratio = [latex] \frac{V_{2}}{V_{1}} ) = \frac{1}{0.2} = 5 [/latex]

∴ 7.86 = [latex] \frac{p_{1}} {5} [1 + \log _{e} 5 ] - 0.28[/latex]

or = 0.522 [latex]p_{1} [/latex] – 0.28 or [latex]p_{1} = \frac{(7.86 + 0.28)} {0.522} [/latex] = 15.59 bar.

Indicated thermal efficiency, [latex] η_{th.(I)} [/latex]:

From steam tables : [latex]h_{1} [/latex]= 2793.4 kJ/kg at 15.59 bar (x = 1) ; [latex]h_{f_2} [/latex] = 282.7 kJ/kg at 2.8 bar

Heat supplied to steam = [latex] \frac{222}{3600}(h_{1} - h_{f_2} ) = \frac{222}{3600}(2793.4 - 282.7) [/latex]

= 154.83 kJ/s

∴ [latex] η_{th.(I)} = \frac{20}{154.83} [/latex] = 0.1292 or 12.92%.

Question 3.14: A single-cylinder double-acting steam engine with 15 cm bore...

Related Answered Questions

A double-acting single-cylinder steam engine runs at 250 r.p.m. and develops 30 kW. The pressure limits of operation are 10 bar and 1 bar. Cut-off is 40% of the stroke. The L/D ratio is 1.25 and the diagram factor is 0.75. Assume dry saturated steam at inlet, hyperbolic expansion and negligible ...

Verified Answer:

Find the gain in thermal efficiency due to the expansive action of steam considering the work done per kg of steam in two engines receiving dry steam at 17.5 bar and exhausting at 0.7 bar, one of them taking steam for whole stroke and other taking steam for 1/5th of the stroke. Assume negligible ...

Verified Answer:

Verified Answer:

Verified Answer:

The cylinder of a non-condensing steam engine is supplied with steam at 11.5 bar. The clearance volume is 1 /10 th of the stroke volume and the cut-off takes place at 1 /4 th of the stroke. If the pressure at the end of compression is 5.4 bar, compute the value of mean effective pressure of the ...

Verified Answer:

A steam engine having swept volume 0.034 m³ and clearance volume 20% of the piston displacement, consumes 2725 kg of steam per hour at 250 r.p.m. The engine is double acting and the pressure of steam near cut-off is 8.8 bar, when piston has traversed 30% of working stroke. If the compression ...

Verified Answer:

Verified Answer:

Verified Answer:

Verified Answer:

A steam engine is governed by varying the initial steam pressure, used 6 kg/kWh when developing 60 kW and 4.65 kg/kWh when developing 150 kW. If steam supplied is 96% dry at 15 bar and a back pressure of 0.36 bar, determine the steam consumption per hour and indicated thermal efficiency when ...

Verified Answer: