Injector Duty Cycle (IDC) refers to the amount of time a fuel injector is open (injecting fuel) relative to the total time available for one engine cycle. It’s expressed as a percentage and is a crucial factor in tuning and ensuring optimal engine performance.
Formula:
Where:
- Injector Pulse Width (ms) = the time the injector stays open during each cycle.
- Time Available per Engine Revolution (ms) = determined by engine RPM (higher RPM means less available time).
Example Calculation:
At 6,000 RPM, a four-stroke engine completes one cycle in 20 milliseconds (since it takes 2 revolutions to complete a cycle). If the injector pulse width is 10 milliseconds, the IDC would be:
Why IDC is Important:
- Optimal Performance: A safe IDC is typically below 80-85% to allow proper injector closing and prevent over-fueling.
- Fueling Limits: If IDC reaches 100%, the injectors are “static,” meaning they are open continuously, which can cause lean conditions and engine damage.
- Tuning Indicator: High IDC suggests the need for larger injectors or adjustments to fuel delivery systems.
How to Reduce High IDC:
- Upgrade to larger fuel injectors.
- Increase fuel pressure (within safe limits).
- Adjust engine tuning (e.g., air/fuel ratio adjustments).