A four-cylinder, four-stroke spark-ignition engine operates at 2800 RPM. The processes within each cylinder can be modeled as an air-standard Otto cycle with a temperature of 280 K and a pressure of 70 kPa at the beginning of the compression process. The compression ratio is 10, and the total engine volume is 2555.6 cm3 . Suppose heat generated from the combustion process (i. e. heat addition per unit mass) is 1080 kJ/kg and air is an ideal gas having variable specific heats. Determine: (a) Total mass of air in the engine (in kg) (6 Points) (b) Determine the power developed by the engine (in hp). (24 Points)

a) Total mass of air in the engine (in kg) = 0.00223 kg

b) power developed by the engine (in hp) = 180.61 hp

Explanation:

Initial temperature,

Initial pressure,

Compression ratio, r = 10

The initial total engine volume,

a) Total mass of air in the engine

Using the gas equation,

Where R = 0.287 kJ/kg-K

70 * 2555.6 * 10⁻⁶ = m * 0.287 * 280

m = 0.00223 kg

b) Power developed by the engine

Heat generated due to combustion,

Compression ratio,

Where Specific capacity of air,  

There are 4 cylinders, k = 4

N = 2800/2

N = 1400

Power developed by the engine,

1 kW = 1.34102 hp

P = 134.68 * 1.34102

P = 180.61 hp

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(b)

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