DETROIT - A new type of high-performance fuel injector starting to appear on European cars could play a big role in helping diesel engines meet stringent U.S. emissions.
It's the piezo injector, a smaller, lighter and faster electronic fuel injector that is expected to debut on an unnamed North American vehicle nameplate in 2008.
In automotive applications such as fuel injectors, crystal structures change shape when electricity is applied. That's known as the piezo electric effect. Piezo is a Greek word that means to apply pressure.
Fuel injectors work like this: Gasoline or diesel fuel from a pump is sent under high pressure to the fuel injector. It enters the engine in a fine, highly atomized spray when a small aperture at the end of the injector is opened and the fuel passes through a nozzle.
How they work
Today's standard-issue fuel injector uses an electrically operated solenoid - an electro-magnet and a spring - to open the aperture.
A piezo injector has small crystalline discs. Those discs expand when electricity is applied. The expanding discs push down on a spring-loaded needle that enables fuel to shoot through the nozzle and into the engine. The fuel is injected at a much higher pressure than with solenoid injectors.
"The crystalline discs expand and contract in the exact same dimensions every time you apply electricity," explains Siemens VDO spokesman Brad Warner. One full stroke takes just .02 milliseconds.
Because the discs are fast-acting, as many as seven injections can be made per piston stroke, compared with two or three for most mechanical solenoid injectors. Multiple injections enable a diesel engine to run smoother and quieter. They also lower combustion chamber temperatures, which reduces oxides of nitrogen or NOx.