SERIES 60 SERVICE MANUAL Intake Stroke During the intake stroke, the piston travels downward, the intake valves are open, and the exhaust valve are closed. The downward stroke of the piston increases the volume in the cylinder and draws in a fresh air and fuel mixture through the intake valves. Compression Stroke At the end of the intake stroke, the intake valves close and the piston starts upward on the compression stroke. The exhaust valves remain closed. At the end of the compression stroke, the air-fuel mixture in the combustion chamber has been compressed by the piston to occupy a space about one-tenth as great in volume as it occupied at the beginning the stroke.
Thus, the compression ratio is 10:1. This act of compression dramatically increases the temperature of the air-fuel mixture, to a temperature below its auto-ignition threshold. It is a timed, externally supplied ignition through the spark plug that actually causes ignition to the mixture. The timed spark is introduced to the cylinder near the end of the compression stroke, which initiates combustion and begins the power stroke. Power Stroke During the power stroke, the piston travels downward and all intake and exhaust valves are closed.
As the throttle is opened to introduce a greater charge of air-fuel mixture to the cylinders, the increasing pressure of combustion against the pistons adds to crankshaft rotation. Exhaust Stroke During the exhaust stroke, the intake valves are closed, the exhaust valves are open, and the piston is on its up stroke. The burning gases are forced out of the combustion chamber through the open exhaust valve port by the upward travel of the piston. All information subject to change without notice. (Rev. 2005) 6SE483 0507 Copyright © 2005 DETROIT DIESEL CORPORATION 7