Question:(II) A four-cylinder gasoline engine has an efficiency of 0.22 and delivers 180 J of work per cycle per cylinder. If the engine runs at 25 cycles per second (1500 rpm), determine (a) the work done per second, and (b) the total heat input per second from the gasoline. (c) If the energy content of gasoline is 130 MJ per gallon, how long does one gallon last?

Short Answer

Expert verified

The work done per second is (a) \(18000\;{\rm{J/s}}\), the total heat input per second is (b) \(8.1 \times {10^4}\;{\rm{J/s}}\) and the time for which one gallon gasoline lasts is (c) \(1604.9\;{\rm{s}}\).

Step by step solution

01

Given Data

The efficiency is \(\eta = 0.22\).

The energy delivered by engine is \(W = 180\;{\rm{J}}\).

The revolution per minute for engine is \(n = 1500\;{\rm{rpm}}\).

The energy content of gasoline is \({Q_{\rm{g}}} = 130\;{\rm{MJ/gal}}\).

02

Understanding power and work done of the engine

The power can be determined by using the standard relation of power and work done. The power is equivalent to the work done by the engine in a unit time.

03

Calculation of work done per second

The relation of work done per second is given by,

\(\begin{aligned}{l}\frac{W}{t} &= \left( {180\;\frac{{\rm{J}}}{{{\rm{cycle}} \cdot {\rm{cylinder}}}}} \right)\left( {4\;{\rm{cylinders}}} \right)\left( {25\;\frac{{{\rm{cycles}}}}{{\rm{s}}}} \right)\\\frac{W}{t} &= 18000\;{\rm{J/s}}\end{aligned}\)

Thus,\(\frac{W}{t} = 18000\;{\rm{J/s}}\) is the required work per second.

04

Calculation of rate of heat input

The relation of efficiency is given by,

\(\begin{aligned}{l}\eta &= \frac{W}{Q}\\Q &= \frac{W}{\eta }\\\frac{Q}{t} &= \frac{W}{t}\left( {\frac{1}{\eta }} \right)\end{aligned}\)

Here, \(\frac{Q}{t}\) is the rate of heat output and W is the work done.

On plugging the values in the above relation.

\(\begin{aligned}{l}\frac{Q}{t} &= \left( {18000\;{\rm{J/s}}} \right)\left( {\frac{1}{{0.22}}} \right)\\\frac{Q}{t} &= 8.1 \times {10^4}\;{\rm{J/s}}\end{aligned}\)

Thus, \(\frac{Q}{t} = 8.1 \times {10^4}\;{\rm{J/s}}\) is the required rate of heat output.

05

Calculation of time consumed by gallon of gasoline

The relation to find the time is given by,

\(t = \frac{{{Q_{\rm{g}}}}}{{\left( {\frac{Q}{t}} \right)}}\)

On plugging the values in the above relation.

\(\begin{aligned}{l}t &= \left( {\frac{{130\;{\rm{MJ/gal}} \times \frac{{{{10}^6}\;{\rm{J/gal}}}}{{1\;{\rm{MJ/gal}}}}}}{{8.1 \times {{10}^4}\;{\rm{J/s}}}}} \right)\\t &= 1604.9\;{\rm{s}}\end{aligned}\)

Thus, \(t = 1604.9\;{\rm{s}}\) is the required time.

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