Problem 15.28 A four-cylinder gasoline engine has an efficiency of 23 % and deli

Question

Problem 15.28

A four-cylinder gasoline engine has an efficiency of 23 % and delivers 230 J of work per cycle per cylinder.

Part A

If the engine runs at 25 cycles per second (1500 rpm), determine the work done per second.

Express your answer to two significant figures and include the appropriate units.

Part B

What is the total heat input per second from the gasoline.

Express your answer to two significant figures and include the appropriate units.

Part C

If the energy content of gasoline is 130 MJ per gallon, how long does one gallon last?

Express your answer to two significant figures and include the appropriate units.

Problem 15.28

A four-cylinder gasoline engine has an efficiency of 23 % and delivers 230 J of work per cycle per cylinder.

Part A

If the engine runs at 25 cycles per second (1500 rpm), determine the work done per second.

Express your answer to two significant figures and include the appropriate units.

Wt =

Part B

What is the total heat input per second from the gasoline.

Express your answer to two significant figures and include the appropriate units.

QHt =

Part C

If the energy content of gasoline is 130 MJ per gallon, how long does one gallon last?

Express your answer to two significant figures and include the appropriate units.

t =

Explanation / Answer

1) Engine fires at 25 cycles/s:

230 J / cycle/ cylinder * 4 cylinders * 25 cycles/second = 23000 J/s
Work = 23000 Joules every second
--------------------------------------...
2) Total heat equals:

23000 J = 23% efficiency so "X" many Joules equals 100% effiicency?
23% / 100% = 23000 / X
solve for X :
X = 100,000 Joules of heat per second
--------------------------------------...

3) 135MJ = 135,000,000 Joules

the engine uses 100000 Joules of heat every second so:

135,000,000 J / 100000J = 1350 seconds of running time or about 22.5 minutes

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