Fuel Injectors

by William Lucas, Clemson Automotive Engineering Graduate Student

Background Information

In the past, carburetors were used to deliver the fuel into the engine of vehicles. Carburetors work on Bernoulli’s principle where essentially as the throttle opens up, air moves faster across the fuel jet drawing more fuel into the intake. However, as emissions requirements became more stringent, carburetors did not give enough control over the amount of fuel injected into the engine. This was problematic because the catalytic converters that were being put on cars to meet the emissions standards require a specific air/fuel ratio to be effective and carburetors are not able to consistently operate in in this narrow range. Because of this, fuel injection became more prevalent in cars, and since 1991, all cars in the United States have been sold with fuel injection. Fuel injectors deliver fuel into the intake port of the cylinder in port fuel injection engines or directly into the cylinder in direct injection engines.

Basic Description

Fuel injectors deliver fuel from the fuel rail into the cylinders by use of a solenoid powered valve. The coils in the solenoid will have electricity applied in short bursts called the pulse width (typically from 2-20ms depending on engine speed and throttle position) which will pull on the valve to open it up spraying the atomized fuel. A spring will reset the valve to the closed position when the solenoid is no long activated.

There are two types of injector tips: pintle and hole/disk type, seen in the image below. Pintle types were the first design and have the valve at the very tip of the injector. It provides good atomization of the fuel, but could easily have deposit buildup on the valve restricting the flow. Hole/disk type fuel injectors fixed the deposit buildup problem by recessing the injectors tip further up the injector and having the fuel spray through a cap with holes drilled in it atomizing the fuel.

Manufacturers

Bosch, AC Delco, Delphi, Venom Performance, Denso, FAST, Holley

For More Information

[1] Carburetor, Wikipedia.

[2] How Fuel Injection Systems Work , Karim Nice, HowStuffWorks.com.

[3] Fuel Injection, Wikipedia.

[4] Venom Hi-Performance Injectors, Venom.

[5] Fuel Injector Operation, YouTube, May 18, 2011.