Some observations found from the above reports:

  • LNG spark ignition engines have higher maintenance costs and lower fuel economy than the diesel engines they replace. The fuel cost must be low enough to compensate for the additional capital and O&M costs.
  • Since there are very few public LNG refueling stations, LNG fleets must have a central terminal where vehicles return regularly to refuel.
  • Diesel-LNG dual-fuel engines have much better fuel economy than equivalent LNG mono-fuel spark ignition engines.
    • Westport HD's ISX-G diesel-LNG engine has about 89.5% of the diesel gallon equivalent (DGE) fuel economy of the ISX diesel engine.
    • Spark-ignition LNG engines have lower DGE fuel economy than their diesel counterparts. Raley's found a 38% lower equivalent fuel economy (or that the LNG truck had 62% of the fuel economy) of a diesel truck. Comparing energy contents, LNG has 57.7% the energy of low-sulfur diesel.
  • Norcal reported tank vacuum issues that appeared to be similar to OCTA's experience.