Mechanical Fuel Injectors Distributor and inline injection pump

Mechanical Fuel Injectors

• Distributor and in-line injection pump systems typically use mechanical fuel injection nozzles

Injection nozzles perform 3 functions • Disperse fuel spray to mix fuel with air • Atomize fuel for efficient combustion • Complete nozzle shutoff to prevent fuel leakage • Injection nozzles in a multi-cylinder engine must provide an equal amount of fuel to each cylinder for smooth and balanced operation.

Injection nozzles • Nozzles are simple devices • Nozzles use a spring to oppose fuel pressure until the right instant for injecting fuel • Nozzle opening pressure can usually be adjusted • Most nozzles today-are closed type • The fuel pressure acts on only one side of the nozzle valve

Closed-type nozzles are classified as: • Inward-Opening Nozzles • • Differential Pressure Hole Type • Outward-Opening Nozzles • Poppet Type Pintle Type • Pintle Type Pintaux Type • Multi-Orifice Type

Inward-Opening Nozzles General Definition • Differential Pressure nozzles, fuel pressure acts against the lower end of the valve and moves the valve inward. • This action allows the nozzle to release a spray of fuel. • A spring at the upper end of the valve can be adjusted to vary the required opening pressure.

Inward-Opening Nozzles Differential Pressure Nozzle • Operated hydraulically-when fuel pressure rises to the set level the nozzle opens against spring pressure and injects fuel • As pressure drops the valve closes and injection stops • The nozzle is adjusted by spring tension for precise operation

Inward-Opening Nozzles Hole Type Nozzle • Addition features not found in differential pressure nozzle • The number and size of spray holes can be varied for a precise spray pattern • Hole type nozzles are best for engines with open combustion chambers

Inward-Opening Nozzles Pintle-Type • Tapered valve that seats in a single orifice located in the valve body • Simply design • Produces a hollow spray and not as versatile as hole-type style

Inward-Opening Nozzles Pintaux-Type • Variation of Pintle, an extra hole is added to the head for spraying fuel at an angle during low engine speed. • This angle also provides startup aid, because it is pointed at the hottest part of combustion chamber

Outward-opening Nozzle • Fuel pressure acts against the valve only in one direction of flow. • Combustion chamber pressure tends to close the valves • Opening pressures tend to be low/fuel leak-off not required

Outward-opening Nozzle Poppet-Type • Opens outward and sprays a fine vapor little penetration

Outward-opening Nozzle Pintle-Type (pencil) • Opens outward, fuel pressure acts on the tapered head to unseat the valve at preset pressure

Outward-opening Nozzle Multi-Orifice • Variation of pintle, fuel is sprayed from a ring of holes instead of past pintle

TESTING INJECTORS • The tip of an injector should always be directed away from you or others. Fuel spray can from an orifice can penetrate clothing and skin. • Enclose nozzle in a container for testing

TESTING INJECTORS • When testing nozzles always refer to the technical manual for that model and application • Test the nozzle for: • Spray pattern and chatter • Opening pressure • Valve leakage • Refer to technical manual for servicing nozzles