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Thermodynamics and engines (A-level only)

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Question 12

During a test run of a prototype bio-methane powered, double-acting, two-stroke reciprocating engine, the following operational metrics were recorded:

  • Rotational speed of the crankshaft: 240 rev min−1240 \text{ rev min}^{-1}240 rev min−1
  • Net area of the indicator diagram for each chamber: equivalent to a work done per cycle of 320 J320 \text{ J}320 J
  • Fuel gas consumption rate: 1.20×10−3 m3 s−11.20 \times 10^{-3} \text{ m}^3 \text{ s}^{-1}1.20×10−3 m3 s−1
  • Calorific value of the bio-methane fuel: 18.0×106 J m−318.0 \times 10^6 \text{ J m}^{-3}18.0×106 J m−3
  • Measured torque at the crankshaft: 75.0 N m75.0 \text{ N m}75.0 N m

The indicator diagrams for the two chambers (left and right) are identical, and each chamber completes one full thermodynamic cycle per crankshaft revolution.

Determine:

a.

The indicated power (PindP_{\text{ind}}Pind​) of the engine.

[3]
b.

The input thermal power (PinP_{\text{in}}Pin​) supplied by the fuel.

[2]
c.

The output (brake) power (PoutP_{\text{out}}Pout​) of the engine.

[3]
d.

The mechanical efficiency (ηmech\eta_{\text{mech}}ηmech​) of the engine.

[2]

Thermodynamics and engines (A-level only) Questions

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