Article Index

There have been several organizations that have evaluated LNG in their fleets. Their experiences are likely very similar to those of other organizations.

Liquid Carbonic

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When Houston Metro began the evaluation of the LNG in 1992, they awarded Liquid Carbonic Inc (LCI) a 7-year LNG fuel supply contract. LCI ordered 5 LNG tractor for LNG distribution fleet, which used the prototype 12.7L spark-ignited DDC S60G engine. Due to Houston Metro's reduced demand for LNG, only 1 of the 5 tractors was used significantly to supply Houston Metro. Three of five LNG tractors eventually ended up in the Jack B. Kelley, Inc. fleet for demonstration purposes in Southern California.

Houston Metro

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The Metropolitan Transit Authority of Harris County, Texas, (Houston Metro) started converting their entire transit fleet to LNG in 1992 to 1996 and by 2002 switched back their entire fleet to clean diesel and diesel hybrid buses. Houston Metro used the DDC 6V92TA PING in their bus fleet, which is a 9.0L two-stroke, V6 diesel-LNG dual fuel engine. There were 10 LNG buses and 5 diesel powered control buses. Tank pressure collapse was one of the problems they encountered due to single line filling. The work-around they came up with was a cryogenic fuel pump to boost fuel pressure. However, the additional equipment inside the fuel tank became another problematic component to maintain. HM also found that fuel loss due to storage over time and during transfer could be as significant as 25%.

DART - Dallas Area Rapid Transit

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DART experience with LNG started with buses powered by the 10L, spark-ignition Cummins L10-280G engine in January of 1998. DART later included Cummins M11-280 powered buses in the evaluation. Although DART seemed to have a strong commitment to LNG with an order of 200 LNG vehicles, by the time the fleet reached a total of 139 by mid-1999, they subsequently cancelled the remaining orders for LNG buses and returned to diesel-powered buses because of poor performance and reliability. Although not directly mentioned in the reports, tank venting could have contributed somewhat to the poorer than expected fuel economy as it would be difficult to measure this blow-off. The Final Results did mention the possibility that the fueler would have to manually open tank vent valve in event of an LNG tank not taking on fuel.

OCTA - Orange County Transportation Authority

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OCTA operates a large fleet of LNG vehicles and is in the process of replacing its entire bus fleet with CNG-powered vehicles or other available or required cleaner-burning fuel. They have had issues with venting of the vehicle LNG tanks because the tanks could not maintain insulating vacuum. Because of the greatly increased heat gain due to vacuum loss, there OCTA buses had much greater than expected venting from the LNG tanks. Rather than trying to resolve heat gain problems, OCTA instead chose to switch the fleet to CNG. At the pumping station, submersible cryogenic pumps contributed additional heat to the fuel, which exacerbated venting problems and caused significant fuel losses.