TA-04 Injector Spray

Tech Corner
Article 04

Fuel Injector Spray Styles

There are several types of Multi-Port fuel injectors. In general, all injector designs are similar. Some are optimized for specific characteristics such as fuel metering, valve response time, low pulse width linearity, and so on. To discuss the actual design differences involves intense injector design theory and is beyond the scope of this article. The focus will be on two areas of injector design that are of interest to most performance enthusiasts, i.e. spray atomization and clogging resistance.

Injector spray atomization begins at the metering orifice. Injectors designed by Robert Bosch Corp. help atomize fuel by “fanning” the fuel into the airstream. The Bosch injector achieves this by using either a pintle valve or multi-hole concept. The pintle design utilizes a needle valve with a formation on the end, called a pintle, which protrudes through the metering orifice. When fuel flows through the orifice it is forced out in the shape of a cone by the pintle. This spray is spread out finely into an approximate 15-30 degree fan.

The multi-hole design does not incorporate a pintle-orifice configuration but instead, a series of orifices drilled out at angles which create a similar cone spray when fuel flows through the holes.

Other injectors such as the type once manufactured by Lucas Automotive emphasize “disc” injector performance over pintle needle valve injectors. The Lucas disc injector design replaced the conventional needle valve with a smaller, lightweight, flat disc. The disc, acting like the needle valve, is pulled off a chimney by the coil’s electro-magnetic force, allowing fuel to flow through holes in the disc, over the walls of the chimney and out of a single metering hole. Because the fuel is metered through a single hole, the fuel exits the injector’s nozzle in a narrow stream, often referred to as a “pencil steam.” When the magnetic field is turned off, the disc slams shut, forming a flat-surfaced seal with the chimney preventing any fuel leakage. This design is very effective in resisting injector clogging since no fuel is present at the tip to evaporate and the metering orifice is tucked inside the injector body away from any heat source.

The low mass of the disc valve allows for quick response times (opening and closing times) which improve the injector’s Dynamic Range capabilities.

A consequential benefit of the Lucas disc injector design is its low noise operation, which virtually eliminates the traditional injector “clicking” sound which is often mistaken for engine valvetrain noise. Figure 2 shows the internal components of the old Lucas disc injector design

Non-pintle injectors were developed to fight injector clogging. It was found that most of the deposits would form on the pintle’s surface which would severely restrict fuel flow through the metering orifice. Removing the pintle from the injector design eliminates a place for the deposits to form thus reducing injector clogging.

In many production engine applications, injector spray patterns play a minimal role in combustion performance because the spray is usually not aimed at the intake valve. Instead, the spray is aimed at the intake runner wall or floor. This is done for many reasons such as for emissions or packaging constraints. In these cases, atomization occurs after the airflow picks-up the fuel either in flight or as it splashes off the runner. In performance applications where emissions are not an issue, injector aiming should be optimized towards the valve and atomization techniques should be utilized. Figure 3 shows various spray patterns of the Bosch injector with different types of metering orifices.

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