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Gas Engines

Bi-Fuel System

  • Overview
  • Applications & Key Technologies

    Gaseous Fuel System™

  • Overview
  • Gas Operating Characteristics
  • Gas Supply
  • Gas Control Components
  • Gas Installation
  • Gas Commissioning
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    Gaseous Fuel Systems

  • Air-Fuel Ratio / LEL
  • Combustion Process
  • Engine Governing
  • Engine Performance
  • Gas-Diesel Ratio
  • Engine Lube Oil
  • Engine Operating Temperatures
  • Engine Efficiency
  • Emissions
  • Engine Warranty
  • Gaseous Fuel System Warranty
  • Gases Fuel System

    General Operating Characteristics

    Air-Fuel Ratio / LEL

    Operation in Gaseous Fuel mode does not appreciably change engine air-fuel ratio. At maximum allowable gas substitution rates (80%), the gas concentration in the intake air is typically less than 3.0% by volume, which is substantially below the 5.0% Lower Explosive Limit (LEL) of methane. Due to the lean condition of the air-gas charge, the possibility of ignition in the engine air-intake system due to backfire or other causes is minimized.

    Combustion Process

    Combustion in Gaseous Fuel mode follows the normal compression-ignition (CI) sequence. The air-gas mixture is admitted to the combustion chamber through the OEM air-intake valve and then compressed during the compression cycle. The high auto-ignition temperature of the lean air-gas mixture prevents ignition of the charge until the diesel injector is activated.

    The injected diesel fuel provides the necessary ignition source for the air-gas mixture which then combusts at a similar speed and pressure compared to 100% diesel operation.

    Although the injected diesel fuel acts as an ignition source for the air-gas mixture, it is also providing a portion of the total energy needed for combustion, based on the set gas-diesel mixture.

    Engine Governing

    The Gaseous Fuel System allows the original engine governing system to control engine speed. No interface or tie-in is required between the Gaseous Fuel System and the engine governor. The Gaseous Fuel System is compatible with electro-mechanical and hydro-mechanical governors as well as some electronic injection based governing systems.

    Engine Performance

    Conversion to GFS Gaseous Fuel typically results in similar performance levels in terms of engine stability, HP, torque and response.

    Gas-Diesel Ratio

    Vehicle duty cycle is the most important variable for determining average gas-diesel ratio.

    In addition to duty cycle, gas composition, charge-air temperature as well as ambient conditions (temperature and altitude) may also play a factor relative to the knock limit of the air-gas mixture.

    In general, moderate to heavy engine loading (over the road conditions) will typically yield gas ratios between 60-75% (assumes high quality natural gas). Lower average engine loads (stop and go / high traffic conditions) will typically limit gas ratio to between 50-60%.

    Engine Lube Oil

    Unless otherwise indicated by gas composition, no changes in engine lube oil specification are required for Gaseous Fuel operation. Natural gas burns with minimum particulate residues so that engine oil may be kept cleaner during Gaseous Fuel operation.

    This can possibly lead to longer average intervals between lube oil and oil filter changes and extended periods between engine overhauls. No changes should be made to the OEM's recommended service intervals without complete engine oil and wear analysis and consultation with the OEM.

    Engine Operating Temperatures

    Engine heat rejection rates while operating in Gaseous Fuel mode are largely similar to 100% diesel performance. Engine exhaust gas temperature, coolant temperature, oil temperature and manifold air temperature levels remain within the limits set by the engine manufacturer.

    Engine Efficiency

    Because the Gaseous Fuel System utilizes a low restriction air-gas mixing device and maintains the excess-air operation of the diesel engine, net fuel efficiency (specific fuel consumption) is normally equivalent to 100% diesel operation. For each unit of diesel fuel displaced during Gaseous Fuel operation, a calorically equivalent unit of natural gas will be needed to maintain engine power.


    Gaseous Fuel operation will typically reduce production of nitrogen oxides, sulfur oxides, reactive hydrocarbons, carbon dioxide and particulates. Exhaust opacity levels (visual emissions) are also typically reduced. For emissions sensitive applications, a 2-way oxidation catalyst is recommended.

    Engine Warranty

    Installation of the Gaseous Fuel System does not generally impact factory engine warranties. Because the engine is not modified from the original design, OEM's typically take the position that the full force and effect of their warranty will remain valid after conversion to Gaseous Fuel .

    Gaseous Fuel System Warranty

    Primary components of the Gaseous Fuel System including mixers, electronic controllers and gas train components are covered by a one year limited warranty.

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