3841197 Volvo.Penta Exhaust manifold

Illustration 1 g01203738
Fuel injection cycle
(1) Screw
(2) Rocker arm
(3) Rack
(4) Upper port
(5) Drilled passage
(6) Plunger
(7) Lower port
(8) Injector barrel
(9) Fuel passage
(10) Needle valve
(11) Piston When plunger (6) is at the top of a stroke, fuel flows from the chamber for the fuel supply, around the injector, and through lower ports (7) and through upper ports (4) of injector barrel (8). As the plunger is moved downward by rocker arm (2), fuel is pushed back into the supply chamber through the lower port. Fuel can also go through drilled passage (5) in the center of the plunger, around the relief groove, and through the upper port of the injector barrel. As the lower port is closed by the bottom of the plunger, fuel can still flow through the upper port until the port is closed by the upper edge of the relief groove on the plunger. At this point, injection starts and the effective stroke of the plunger begins.During the effective stroke, fuel is injected into the cylinder until the downward movement of the plunger allows the scroll (helix) to open the lower port. This downward movement of the plunger also releases the fuel pressure. The amount of fuel that is injected during the effective stroke is determined by the position of the scroll in relation to the lower port.Fuel goes through the center passage of the plunger and fuel goes through the lower port during the remainder of the downstroke. As the lower port is opened, the sudden release of very high pressure causes the fuel to hit the deflector for spills with a high force. The deflector for spills gives protection to the injector housing from erosion because of the force of the released fuel. On the return stroke, the injector barrel is filled with fuel again from the fuel supply chamber.The plunger can be turned by rack (3) while the plunger is moved upward and the plunger is moved downward by the rocker arm. The upper part of the plunger has a flat side that fits through the gear. The gear is engaged with the rack. The plunger slides upward and the plunger slides downward in the gear. As the rack moves, the gear and the plunger rotate together. This rotation of the plunger controls the fuel output of the injector. The rotation of the plunger changes the relation of the scroll to the lower port in the injector barrel. The rotation of the plunger also increases or the rotation decreases the length of the effective stroke for injection. The scroll can set the amount of fuel per injection stroke. Therefore, the fuel rate to the engine can be controlled in relation to different engine loads.No injection takes place during the downstroke of the plunger when the rack is moved all the way against the fuel injector body. This is the "Fuel Off" position. Fuel injection begins when the rack is moved outward by a small distance. As the rack continues to move outward, the amount of fuel that is injected into the cylinder is increased until the maximum fuel position is reached.During the fuel injection stroke, fuel passes from the injector barrel through a valve assembly. The valve assembly has a spring-loaded needle valve (10) and fuel flows through fuel passages (9) around the needle valve to the valve chamber. The fuel pressure lifts the needle valve off the seat. The fuel can now flow through the orifices in the tip into the combustion chamber.If the needle valve is held open between injection cycles by small debris, then gases from combustion could enter the injector. The gases will cause damage. A flat check valve is used above the needle valve in order to keep these high pressure gases from combustion out of the injector. The injector operates with the flat check valve until the foreign particle has been washed away through the orifices by the fuel and normal operation again takes place.The tip of the injector extends a short distance below the cylinder head into the combustion chamber. The tip has several small orifices that are evenly spaced around the outside diameter in order to spray fuel into the combustion chamber. The top surface of piston (11) is designed with a shaped crater that causes the air to swirl. The fuel is sprayed into the air that is swirling for more complete combustion.