Fuel injection principle
Fuel injection: fuel enters cylinders directly or just ahead of intake valve. No carburettor mixing (PHAK ch.7).
Six basic components:
- Engine-driven fuel pump
- Fuel-air control unit
- Fuel manifold (fuel distributor)
- Discharge nozzles
- Auxiliary fuel pump
- Fuel pressure/flow indicators
Flow (tank to cylinder):
| Step | Part | Job |
|---|---|---|
| 1 | Engine-driven pump | After start, sends pressurized fuel to control unit |
| 2 | Fuel-air control unit | Replaces carburettor. Meters fuel by mixture control setting. Sends it to manifold valve at throttle-set rate |
| 3 | Fuel manifold valve | Distributes fuel to nozzles |
| 4 | Discharge nozzles | One per cylinder head. Inject directly into cylinder intake port |
Advantages:
- Less evaporative icing
- Better fuel flow
- Faster throttle response
- Precise mixture control
- Better fuel distribution
- Easier cold weather starts
Disadvantages:
- Hard hot-engine starts
- Hard restart after engine quits from fuel starvation
Trap: injection makes cold start easier, hot start harder.
References
- PHAK ch.7 (Fuel Injection Systems)