Series 50 – Section 2.39 Overview of the Low Pressure Fuel System for the Series 50G Generator Set Engine (1998 and Later)

Section 2.39
Overview of the Low Pressure Fuel System for the Series 50G Generator Set Engine (1998 and Later)

The purpose of the fuel system is to store the fuel, keep it clean and free from air, water, or other impurities and to deliver it to the combustion chamber at the correct pressure, temperature, air and fuel mixture. The Series 50G engine requires an adequate fuel supply for proper performance and to develop full rated power. This section describes the Detroit Diesel Series 50G compressed natural gas fuel system.‪

The following are DDC supplied parts:‪

  • Pulse width modulated stepper motor valve (PSV)
  • Low pressure regulator
  • Venturi fuel mixer
  • Regulator hoses
  • Air inlet tube

The following are OEM supplied parts:‪

  • Gas inlet pipe
  • Genset controlled gas shutoff valve

The fuel system uses computer calculations for both fuel flow and air flow, while maintaining a lean air - fuel mixture for low emissions and good fuel economy. Calculations are based on knowing the temperature of the air and fuel along with the temperature and pressure of the fuel and air mixture in the inlet manifold. The air temperature sensor is located in the air intake tube located in front of the gas mixer. The fuel temperature sensor is located in the gas mixer. An intake manifold pressure sensor is located in the intake manifold. See Figure "Series 50G Generator Set Engine — Right Side, Rear View" and see Figure "Series 50G Generator Set Engine — Left Side, Front View" .‪

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 1. Fuel Mixer Assembly‪

 7. Air Inlet Tube‪

 2. Pulse Width Modulated Stepper Motor Valve‪

 8. Thermostat Housing‪

 3. Fuel Supply Hose‪

 9. Exhaust Manifold‪

 4. Fuel Balance Hose‪

10. Fresh Water Pump‪

 5. Low Pressure Regulator‪

11. Turbocharger‪

 6. Air Balance Hose‪

12. Lube Oil Filters‪

Figure 1. Series 50G Generator Set Engine — Right Side, Rear View

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 1. Vibration Damper‪

 7. Throttle‪

 2. Crankshaft Pulley‪

 8. Rocker Cover‪

 3. Accessory Drive Assembly‪

 9. Intake Manifold‪

 4. Alternator Drive Belt‪

10. Electric Control Module‪

 5. Fan Pulley‪

11. Electric Starting Motor‪

 6. Alternator‪

12. Oil Filter‪

13. Dipstick‪

Figure 2. Series 50G Generator Set Engine — Left Side, Front View



To avoid injury from an explosion of natural gas, the following precautions must be taken:‪

  • Use a combustible-gas detector. Liquefied natural gas (LNG) is odorless and cannot be detected by smell. Compressed Natural gas (CNG) may be odorless and may not be detected by smell.
  • Equipment fuel systems are the responsibility of the Original Equipment Manufacturer (OEM). Equipment fuel system guidelines must be closely adhered to when installing or servicing equipment. Refer to OEM guidelines specifying which maintenance procedures require venting of fuel lines and fuel tanks.
  • LNG systems are pressurized and contain extremely cold (-162° C [-260° F]) fluids. Contact the fuel supplier or OEM for LNG safety requirements. Contact with LNG may cause personal injury (freezing).
  • Vent systems on the equipment should be ducted to a safe area whenever equipment is in an enclosed area.


To avoid injury from arc welding, gas welding, or cutting, wear required safety equipment such as an arc welder's face plate or gas welder's goggles, welding gloves, protective apron, long sleeve shirt, head protection, and safety shoes. Always perform welding or cutting operations in a well ventilated area. The gas in oxygen/acetylene cylinders used in gas welding and cutting is under high pressure. If a cylinder should fall due to careless handling, the gage end could strike an obstruction and fracture, resulting in a gas leak leading to fire or an explosion. If a cylinder should fall resulting in the gage end breaking off, the sudden release of cylinder pressure will turn the cylinder into a dangerous projectile. Observe the following precautions when using oxygen/acetylene gas cylinders:‪

  • Always wear required safety shoes.
  • Do not handle tanks in a careless manner or with greasy gloves or slippery hands.
  • Use a chain, bracket, or other restraining device at all times to prevent gas cylinders from falling.
  • Do not place gas cylinders on their sides, but stand them upright when in use.
  • Do not drop, drag, roll, or strike a cylinder forcefully.
  • Always close valves completely when finished welding or cutting.

The Series 50G engine low pressure fuel system consists of a venturi type fuel mixer, Pulsewidth Modulated Stepper Motor Valve (PSV), throttle actuator, and low pressure regulator. It is referred to as a "demand" system in that the venturi mixer generates a suction at the regulator outlet. The regulator adjusts its outlet pressure in response to the demand (suction) of the venturi resulting in an increase of fuel flow. The opposite is true for conditions requiring a decrease in fuel flow. See Figure "Low Pressure Natural Gas Fuel System (Series 50G)" .‪

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Figure 3. Low Pressure Natural Gas Fuel System (Series 50G)

Fuel supply is routed to the inlet side of the low pressure regulator at a pressure of 1-5 kPa (5-20 in. H2 O). The low pressure regulator is a "balanced" regulator and as such, reduces this pressure to a level approximately equal to air inlet pressure.‪

Regulated fuel is routed from the low pressure regulator to the PSV. The PSV is fully controlled by DDEC III/IV and is used to bias fuel flow, rich or lean, based on a predetermined engine calibration.‪

Fuel from the PSV enters the venturi mixer where it is drawn into and mixed with the airstream ahead of the turbocharger compressor inlet, charge air cooler, throttle and intake manifold.‪

Series 50 Service Manual - 6SE50
Generated on 10-13-2008

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