High Pressure Fuel Circuit

Courtesy of NISSAN NORTH AMERICA, INC.

ECM controls fuel rail pressure by controlling the quantity control valve according to a signal transmitted from the fuel pressure and temperature sensor and adjusting fuel pressure necessary to the direct injection in the high pressure circuit to approximately 20 MPa (200 bar, 204 kg/cm ² , 2, 900 psi).

The high pressure fuel pump pressurizes fuel sent from the fuel pump up to approximately 20 MPa (200 bar, 204 kg/cm ² , 2900 psi) and pumps the pressurized fuel to the fuel rail. In addition, the high pressure fuel pump has a fuel pressure damper to control pressure fluctuation occurring at rapid acceleration, contributing to the reduction in fuel fluctuation. Since the high pressure fuel circuit does not have a return circuit, the pressure increases up to 27 MPa (270 bar, 275.4 kg/cm ² , 3, 915 psi) due to temperature rise in the high pressure fuel circuit after engine stop or in deceleration mode. The pressure drops to 13 MPa (130 bar, 132.6 kg/cm ² , 1, 885 psi) only at vehicle standstill and for a selector lever position "N" or "P" in order to reduce the noise emissions from the fuel system high pressure pump. In the case of shutting off a vehicle with a hot engine, the fuel pressure can increase up to 25 - 26.7 MPa (250 - 267 bar, 255 - 272.34 kg/cm ² , 3, 625 - 2, 871.5 psi) in the fuel high pressure circuit. Upon reaching this threshold a valve opens in the fuel system high pressure pump and the pressure is reduced. Upon starting the engine the pressure falls rapidly to the normal operating pressure of about 20 MPa (200 bar, 204 kg/cm ² , 2, 900 psi).

During regulation of the fuel high-pressure circuit one differentiates between the following operating conditions.

• Start
• Normal mode
• Low-pressure limp-home mode (fuel high pressure is not reached)
• Stop

Start 

• The quantity control valve is energized and closed, so there is full delivery from the fuel system high pressure pump and rapid pressure buildup.
• Fuel pump pressure is approx. 450 - 670 kPa (4.5 - 6.7 bar, 4.59 - 6.834 kg/cm ² , 65.25 - 97.15 psi).

Normal mode 

• The quantity control valve regulates the supplied and the required fuel quantity over the duty cycle.
• Fuel pump pressure is dependent on the fuel temperature between approx. 300 - 550 kPa (3 - 5.5 bar, 3.06 - 5.61 kg/cm ² , 43.5 - 79.75 psi).
• The fuel predelivery pressure is dependent on the engine speed and fuel temperature and varies between 450 - 670 kPa (4.5 - 6.7 bar, 4.59 - 6.834 kg/cm ² , 65.25 - 97.15 psi) (absolute).

Low-pressure limp-home mode (fuel high pressure is not reached) 

• The quantity control valve is de-energized and therefore opened.
• Fuel pump pressure about 450 - 670 kPa (4.5 - 6.7 bar, 4.59 - 6.834 kg/cm ² , 65.25 - 97.15 psi), fuel flows over the open quantity control valve into the rail.
• Actuation of fuel injectors extended.
• Reduced performance, max. speed approx. 70 km/h (43.49 MPH).

Stop 

• Quantity control valve is de-energized and opened.
• Fuel pump not actuated.