  We study the heat engine by a $d$-dimensional charged anti-de Sitter black
hole by making a comparison between the small-large black hole phase transition
and the liquid-vapour phase transition of water. With the help of the first law
and equal-area law, we obtain an exact formula for the efficiency of a black
hole engine modeled with a Rankine cycle with or without a back pressure
mechanism. When the low temperature is fixed, both the heat and work decreases
with the high temperature $T_{1}$. And the efficiency increases with $T_{1}$,
while decreases with the charge $q$. For a Rankine cycle with a back pressure
mechanism, we find that both the maximum work and efficiency can be approached
at the high temperature $T_{1}$. In the reduced parameter space, it also
confirms the similar result. Moreover, we observe that the work and efficiency
of the black hole heat engine rapidly increase with the number of spacetime
dimensions. Thus higher-dimensional charged anti-de Sitter black hole can act
as a more efficient power plant producing the mechanical work, and might be a
possible source of the power gamma rays and ultrahigh-energy cosmic rays.
