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Thermodynamics and engines (A-level only)

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Question 12

During a performance evaluation of a secondary energy harvester in a geothermal power plant, a custom-designed double-acting, two-stroke gas engine was tested. The following baseline operational parameters were recorded:

  • Rotational speed of the crankshaft: 210 rev min−1210 \text{ rev min}^{-1}210 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
  • Gaseous fuel consumption rate: 8.50×10−4 m3 s−18.50 \times 10^{-4} \text{ m}^3 \text{ s}^{-1}8.50×10−4 m3 s−1
  • Calorific value of the gaseous fuel: 24.0×106 J m−324.0 \times 10^6 \text{ J m}^{-3}24.0×106 J m−3
  • Measured brake torque at the crankshaft: 82.0 N m82.0 \text{ N m}82.0 N m

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

Determine:

a.

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

[2]
b.

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

[2]
c.

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

[3]
d.

The mechanical efficiency (ηmech\eta_{\text{mech}}ηmech​) of the engine, expressed as a percentage.

[2]
Markscheme

Thermodynamics and engines (A-level only) Questions

  1. A Level
  2. /Physics
  3. /Thermodynamics and engines (A-level only)

29 exam-style questions on AQA A Level Physics Thermodynamics and engines (A-level only), covering First law of thermodynamics (A-level only), Non-flow processes (A-level only), The $p$ - $V$ diagram (A-level only), Engine cycles (A-level only), Second Law and engines (A-level only), and Reversed heat engines (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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