CNG Case Studies Highlight Performance

CNG Case Studies Highlight Performance

May 24, 2013

The Colorado Energy Office has done a case study analysis of natural gas use. The report presents real-world experiences with compressed natural gas in heavy trucks and pickups used in three fleets: The City of Grand Junction [Colo.], Republic Services, and Denver International Airport.

Here are some highlights from the municipal fleet.

Grand Junction reported a variety of changes in preventive maintenance procedures.

  • “One specific item cited by Grand Junction fleet supervisor Tim Barker is the need for specialized spark plugs for the refuse trucks. The plugs need changing every 1,500 to 2,000 hours of vehicle use. Each engine requires six spark plugs, costing $75 each.”
  • “Another issue is related to the presence of ‘heavy ends’ or ‘heavy oils’ that can separate out from the CNG in the compressors. There is a specific coalescing filter for the heavy ends on the vehicles that requires daily draining. If it is not drained regularly, in Grand Junction’s experience the oil can get into the CNG fuel system and cause maintenance issues. Maintenance technicians at Grand Valley Transit were only draining this oil once per week, which resulted in performance issues. They have since adopted the once-per-day recommendation, and this has addressed the performance issues.”

Grand Junction staff trained themselves using manuals provided by the engine manufacturer.

  • “Cummins Westport operates a virtual college for engine maintenance, which was a very helpful training tool for the vehicle technicians. Cummins Westport offers training CDs that the maintenance technicians watch during downtime or in dedicated training sessions. Three employees were also sent to an in-person CNG training hosted by Cummins Westport in Las Vegas.”
  • “One reported challenge is the inconsistency in maintenance recommendations among different sources, including engine manufacturers, truck manufacturers, and third-party training courses. For example, Cummins Westport suggests different routines than the truck manufacturers and third- party training courses.”

In most cases, the city offset the increased cost of a CNG truck with fuel savings. Application affected the extent of the cost recovery.

  • “The city paid for the first two CNG vehicles from its 2010 budget without any external funding. The city anticipated that fuel savings would offset the incremental cost of the CNG vehicles over time. Since the initial purchase, Grand Junction has purchased and received three additional CNG refuse trucks and purchased three more that are on order.”
  • “The city also purchased a CNG dump truck. The city will not directly recover the $6,000 incremental cost of the CNG dump truck within the vehicle’s lifetime because of its modest use profile. The city decided that the energy and environmental benefits of CNG justified the additional purchase costs of the vehicle.”

The city also built its own fueling stations: a time-fill station and  fast-fill station. The fast-fill is open to the public and operated by a private company on property leased from the city.

  • “The time-fill station has 10 dispensers. Average monthly fuel throughput for the time-fill station was 2,185 DGE for the most recent 12-month period. During that period, the maximum throughput in a single month was 3,999 DGE, occurring in April 2012. When a CNG truck comes in for fueling, the driver connects the pump nozzle to the fuel tank. The truck then fuels unattended, reducing labor time needed for fueling. This process takes 2.5 to 3 hours if the truck’s fuel tank is empty.”
  • “The fast-fill station looks more like a traditional gas station with a digital display, card reader, and pump nozzle. Anecdotal experience suggests that the fast-fill station can sequentially fuel up to five cars fully, and most of a sixth, an unusual occurrence for the fast-fill pump. After such an occurrence, the compressor will need to run for 2 to 2.5 hours to refill the storages spheres. Average monthly throughput for the fast-fill station is 661 DGE in the most recent 12 month period, with a maximum of 1,830 DGE for a single month.”