Traditional diesel injectors use electromagnetic, or solenoid, controls. The electronic engine management system sends an electrical signal to activate the mechanical valve that controls fuel flow through the injector.
The technology is well-known, reliable, cost-effective, and the unit is physically smaller than piezo units. But solenoid injectors tend to vibrate more than piezo units, creating more noise.
In a piezo injector, the electronic engine management system also sends an electrical signal to the valve. But the unique property of a piezo crystal is that it changes shape when exposed to electric current. The actual movement is microscopic, but enough to make the piezo element act as the valve. Piezo injectors are quieter and more precise than solenoid units, a benefit in a microsecond environment, but they are more expensive.
In both cases, the common-rail principle remains the core of diesel injection systems. A single (common) high-pressure fuel line is connected to individual injectors at each cylinder.
The electronic engine management system controls the precise opening and closing of the fuel-flow valve in each injector. Increased injector pressure requires higher pressure in the common-rail system.
Rival diesel fuel-injector suppliers are fighting a technology duel to win new business as tougher EU emissions rules take effect before the end of the decade.
