Fuel Rail Pressure Relief

A major source of engine-off evaporative hydrocarbon emissions is fuel injector leakage. Methods and devices to relieve fuel rail pressure after key-off, and thus reduce leakage are introduced. Impact on fuel manifold re-pressurization is considered.

The basic principles governing this behavior: fuel thermal expansion, fuel vapor pressure, and dissolved gasses in liquid are elaborated. Fuel pressure relief data is shown.