The use of Liquefied Natural Gas (LNG) in transport is a suitable option to power, large long distance trucks in areas where gas is transported as LNG because there are indigenous gas supplies and no gas network. The use of LNG in passenger cars is far less viable because on average passenger cars stand idle more often, which would give rise to high evaporative losses. The use of LNG requires storage facilities for the cold (-162 0C) liquid natural gas at the roadside refueling stations and special fuelling equipment which can handle cryogenic temperatures. In addition, the trucks must be equipped with special dual fuel engines to be able to use LNG. Moreover, the fuel tank on board of the truck needs to be adapted for LNG usage. These requirements make the use of LNG relatively expensive. Nevertheless, the use of LNG in the transport sector can still have substantial environmental benefits. It is reported that a truck powered by a dual fuel LNG-diesel engine can emit up to 75% lower NOx emissions and about 13% lower Well-To-Wheel CO2 emissions compared to diesel powered trucks. Overall, the technology to use LNG as a transport fuel is well developed, but is expected to remain a niche market.
Special LNG trailers can deliver the liquid fuel from the storage tanks to LNG fueling stations. At the site of the fueling station the LNG has to be stored in very well insulated tanks. The insulation only, however, will not keep the temperature of LNG low enough. LNG is stored as a so called "boiling cryogen", a very cold liquid at its boiling point which stays at the low temperature by evaporative cooling. (McMullen et al, 2002) As long as the LNG vapor is allowed to leave the storage tank, the temperature will remain constant. At the refueling site this boil off natural gas vapor can be compressed to CNG (Compressed Natural Gas) and be sold to passenger cars. This fuel type is called “LCNG”, Liquefied Compressed Natural Gas and is preferable for passenger cars.
The use of LNG in vehicles is a tradeoff between the duty cycle (i.e. the time in operation) of the vehicle and the evaporation rate (boil off rate). In general the annual mileage of passenger cars is too low to compensate for the boil off losses. However, the direct use of LNG can be an attractive alternative for heavy duty vehicles, which travel high mileages in one go.
Feasibility of technology and operational necessities
Boil off (evaporation) losses in the fuel tank of the vehicle require a high mileage of the vehicle and make the direct use of LNG only economically feasible for Heavy Duty trucks. LNG has a much higher storage density than compressed natural gas, making it more suitable as an alternative to diesel fuel than compressed natural gas (California Energy Commission, 2006). However, the heavy duty trucks need to be equipped with a special natural gas diesel dual-fuel engines (Frailey, 1998). Moreover, sufficient special refueling stations are needed with a storage tank for the cold liquid natural gas. The boil off losses at the site of the fueling station can be compressed to CNG and be used in passenger cars.
Status of the technology and its future market potential
Contribution of the technology to protection of the environment
Financial requirements and costs
Figure 1: Investment costs for LNG production and distribution according to a Swedish case study (source: Petterson, 2006)
In comparison a conventional CNG fuelling station where the natural gas is supplied by pipeline costs around $ 500.000 (Roeterdink et al, 2010). The financial benefit of LNG usage over CNG lays mainly in the lower transport costs, which makes to use of LNG only cost effective in large countries.
Figure 2: Distribution costs as function of the transport distance
- Clean Energy (2008): The Clean Energy California LNG Plant. Available at http://www.cleanenergyfuels.com/pdf/CE-OS.Boron.pdf
- California Energy Commission (2006): Liquefied Natural Gas (LNG) as a transportation fuel. Available at http://www.consumerenergycenter.org/transportation/afvs/lng.html
- Centre for Energy Economics (2006). How much does LNG cost. Available at http://www.beg.utexas.edu/energyecon/lng/LNG_introduction_09.php
- Frailey (1998): Development of LNG-powered Heavy Duty trucks in Commercial Hauling. M. Frailey, NREL/SR-540-25154, December 1998
- Kroon, P. (2009): Ketenemissies van nieuwe transportbrandstoffen: Broeikasgasemissies van winning tot verbruik (Concept rapport). Unpublished
- McMullen et al, (2002): New technologies and alternative fuels: Working paper on Alternative propulsion and fuel technology review. John J. McMullen Associates Inc with Booz Allen Hamilton
- McPherson, C. (1999): Natural Gas, private sector participation and market development,
- Petterson (2006): LCNG Study - possibilities with LNG supporting supply of methane as a vehicle fuel in Sweden. Vattenfall 2006-11-21: A. Petterson, S. Liljemark and M. Losciale.
- Roeterdink, W.G., Uyterlinde, M.A., Kroon P. and Hanschke, C.B. (2010): Groen Tanken: Inpassing van alternatieve brandstoffen in de tank- en distributie infrastructuur. ECN report E—09082