Glossary of Terms

Closing Time (CT)

This time is a measurement of the time required for the armature of the injector to first reach the fully closed position after the driver’s circuit pulse was terminated.

Duty Cycle
This is a calculation derived from the amount of time that an injector is turned on or energized. Safe operating duty cycle is commonly stated at 85%. However, most injectors tend to run static after 92%. Running “static” means the injector is Fully open 100% of the time.

Dynamic Flow (Qd)
This is the measurement of fuel delivered per pulse of the injector when it is energized at a specific Pulse Width (PW) rather than fully energized.

Dynamic Flow Rate (Q) Q = Qd / P
Impedance A term used to describe the resistance of the injector’s coil. A low impedance injector typically has a resistance of less than 3 ohms and a high impedance injector has a resistance of more than 10 ohms.

Injector Driver
A circuit supplying voltage to an injector for a predetermined time at a predetermined rate.

Gasoline Direct Injection (GDI)
A newer method of fuel injection where fuel is injected directly into the combustion changer rather than the intake system. GDI systems operate at much higher pressures than traditional MPI or SFI systems.

Multiport Fuel Injection (MPI)
Each cylinder uses a dedicated fuel injector positioned in the intake manifold above the intake valve. I n most MPI systems, the injectors all fire at once every revolution of the crankshaft. The fuel for one combustion cycle is delivered in two pulses.

Opening Time (OT)
This time is a measurement of the time required for the armature of the injector to first reach the fully opened position after the initiation of the driver’s circuit pulse input.

Peak & Hold
Uses two levels of current to operate the injector. The driver applies a predetermined voltage to the injector. Once this voltage level is reached (Peak), the driver is held (Hold) at a lower level for the durration of the Pulse Width. The use of the higher Peak current minimizes injector (“lag”) OT while holding it open at the lower current reduces the time it takes for an injector to close (CT). Heat is disapated at the injector in a P&H driver.

Period (P)
The time elapsed from the beginning of one injection pulse to the beginning of the next pulse. Expressed in units of PW (ms/pulse)

The valve inside the injector and its seat, usually located at the tip of the injector. The shape of the pintle determines the spray pattern.

Pressure across the injector at which the test was performed.

Pulse Width (PW)
The time, measured in ms, that the injectors are programmed to deliver fuel for a single injection event. (ms/pulse)

Turns on 100% for the entire duration of the injector Pulse Width and is used with High impediance coils. Heat is usually disapaded through the injector itself or through a resistor rather than the injector driver circuit. The slower response of this system dereases the usable flow rage of the injector increasing OT and decreasing CT.

Sequential Fuel Injection (SFI)
Each cylinder uses a dedicated injector like the MPI system. The injectors are fired individually in cylinder firing order on a sequential system. The fuel for one combustion cycle is delivered in one pulse instead of two.

The change in Dynamic Flow (Qd) per unit of Pulse Width (PW) determined by the calculated linear regression flow curve.

Static Flow Rate (Qs)
The maximum flow rate of an injector when energized in the fully open position usually measured in g/s or mg/pulse.

Usable Pulse Width Range
A relative measurement of the total time for an injector to fully open and fully close.