18.For a diesel engine an initial downward stroke of the piston draws in the air to charge the cylinder,which is followed by the compression stroke, with the fuel being injected as top dead center isapproached, then a downward power stroke, and an upward exhaust stroke. Which type of engineis called for this operation?
(A)Two-stroke engine
(B)Four-stroke engine
(C)Supercharging engine
(D)Ideal cycle engine