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Understanding HPDI Natural Gas Fuel Systems A1

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  • Understanding HPDI Natural Gas Fuel Systems A1

    By Paul Pate, Training Manager, NGVi

    There are two different types of natural gas engines and systems for the heavy-duty natural gas market: spark ignited and compression ignited. Spark-ignited systems are by far the most numerous, and account for more than 90% of the market. There is a limited number of compression-ignited systems available. These systems, which only exist as dual-fuel systems, come in two types: substitution systems and high-pressure direct injection (HPDI) systems.

    Substitution systems simply add natural gas to the diesel fuel, "substituting" a percentage of the diesel with natural gas. These trucks will run either on natural gas mixed with diesel or pure diesel, but will not run on natural gas only. The substitution percentage of diesel with natural gas ranges between 0-65%, dependent upon load and operating conditions. This type of system accounts for the majority of dual-fuel diesel/natural gas engines.


  • #2
    The compression ratio of an engine with Westport™ HPDI is the same as the diesel engine on which it is based, which results in fewer changes to engine components and preservation of the fuel economy benefits associated with high compression.

    Westport’s proprietary, patented HPDI technology utilizes the same Diesel thermodynamic cycle used by diesel fuel. This Diesel cycle is inherently more efficient than the Otto thermodynamic cycle used by spark ignited (SI) gasoline and natural gas engines.

    Westport™ HPDI uses natural gas as the primary fuel along with a small amount of diesel as an ignition source. The two fuels are not pre-mixed with the intake air before they enter the combustion chamber so there is no risk of engine knock and therefore no need to lower the compression ratio and peak torque output. As compared to diesel fuel, directly injected natural gas burns with a lower adiabatic flame temperature and has a low propensity to the formation of carbon particles and therefore offers inherent nitrous oxide (NOx) and particulate matter (PM) emissions benefits.


    • #3
      American Power Group said today that it’s taking its dual fuel technology to British Columbia, having signed authorized dealer and certified installer agreements for its Turbocharged Natural Gas V5000 hardware with Cullen Diesel Power.

      The first ten APG dual fuel systems will be installed on conversions for Clark Freightways of Coquitlam, B.C.