Compressed natural gas (CNG) and liquefied natural gas (LNG) are both composed primarily of natural gas, or methane (CH4). It is produced either from gas wells or in conjunction with crude oil production.
Natural gas is used for a range of energy purposes, including transport fuels.
Under the right circumstances natural gas can be an environmentally responsible transport fuel. For example, trials conducted in Australia and overseas show that the best natural gas technology available today can reduce greenhouse gas emissions by around 20 per cent. There can also be fuel cost savings. However, to make these kinds of savings, engines must be optimised to run on natural gas.
While CNG and LNG have a lower energy content than either petrol or diesel, their environmental performance in terms of exhaust emissions and the availability of abundant natural gas reserves in Australia makes them a potentially viable alternative transport fuel.
CNG and LNG are predominantly used in Australia in the heavy vehicle market in specialist applications such as metropolitan bus fleets, garbage trucks and line haulage. LNG as a heavy duty vehicle fuel is a recent development; improvements in vehicle tanks, storage vessels and gas dispensers have all contributed to its adoption by heavy vehicle fleets and bus and locomotive operators. LNG-fuelled vehicles have ranges and refuelling times comparable to those of diesel-fuelled vehicles without any power to weight disadvantages. Vacuum-insulated LNG storage tanks are designed to replace the diesel units without any vehicle modifications, minimising down time for truck/bus conversions.
The use of CNG as a transport fuel presents a number of practical impediments. For example CNG needs to be stored under pressure and requires specialised heavy-duty storage tanks on board the vehicle. These storage tanks affect the amount of fuel that a vehicle can carry and its operating range, therefore limiting its broader application within the Australian vehicle fleet.
Further, natural gas fuels require abundant, appropriately placed, specialist refuelling facilities that are not readily adaptable to, or available across, Australia's petroleum distribution infrastructure. Home based natural gas refuelling systems which can be connected to reticulated gas are becoming available in the market.