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Figure 4 shows some of the equipment used to investigate the thermal and mechanical efficiencies of a single-cylinder four-stroke petrol engine - AQA - A-Level Physics - Question 3 - 2020 - Paper 5
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Figure 4 shows some of the equipment used to investigate the thermal and mechanical efficiencies of a single-cylinder four-stroke petrol engine. - Petrol is supplie... show full transcript
Worked Solution & Example Answer:Figure 4 shows some of the equipment used to investigate the thermal and mechanical efficiencies of a single-cylinder four-stroke petrol engine - AQA - A-Level Physics - Question 3 - 2020 - Paper 5
Step 1
How to determine the input power
Answer
To determine the input power, we need to measure the fuel consumption rate. This can be done by using a calibrated fuel reservoir and measuring the volume of petrol consumed over a set time interval. The input power can be calculated using the formula:
ho_f imes g}{t} $$ where: - $P_{in}$ is the input power in watts, - $V_f$ is the volume of fuel consumed in cubic meters, - $\rho_f$ is the density of petrol (approximately 720 kg/m³), - $g$ is the calorific value of petrol (approximately 34.2 MJ/kg), and - $t$ is the time in seconds.Step 2
How to determine the indicated power
Answer
The indicated power can be calculated using a pressure measurement taken from the sensors above the piston. The formula for indicated power (IP) is given by:
IP = rac{P_m imes V_{s}}{60}
where:
- is the mean pressure inside the cylinder,
- is the swept volume of the piston.
Step 3
How to determine the brake power
Answer
Brake power (BP) can be determined by using the dynamometer to measure the torque it transmits to the output shaft. The formula for brake power is given by:
u}{60} $$ where: - $\tau$ is the torque in Newton-meters, - $\nu$ is the rotational speed in revolutions per minute.Step 4
Step 5