A cam phaser is mounted on the exhaust camshaft of a diesel engine and is operable
to selectively advance timing of only the exhaust valves relative to a nominal
position. The purpose of advancing timing of the exhaust valves is to advance valve
closing sufficiently to shorten the effective exhaust strokes of the pistons and
thus increase the trapped hot exhaust residuals. This occurs when the exhaust valves
close earlier than piston top dead center in the normal exhaust stroke phase of
engine operation. This increases the in-cylinder temperature so that combustion
stability and hydrocarbon emissions are improved.
