It was recently announced that Shell had entered into an agreement with Vancouver-based Westport Innovations to promote the wider use of liquefied natural gas (LNG) as an alternative fuel in North America, mainly for commercial vehicles, by helping to consolidate fuel supply and customer support by way of specialised after-sales services.
Natural gas as a vehicle fuel, mainly in compressed form (CNG), is already in widespread use, especially in parts of the world adjacent to gas fields. In such situations, the cost of getting the gas, often by pipeline, to the point of use – typically the depot of a large truck or bus fleet – is relatively modest. There are powerful lobby groups such as the Natural Gas Vehicle Association, with astute publicity machines behind them, which have succeeded in boosting the profile of CNG as an automotive fuel. However, its penetration into a market dominated by diesel power remains limited.
Moving from diesel to CNG or LNG fuelling usually brings ongoing fuel cost savings.
LNG is the same fuel as CNG but lowered in temperature to cryogenic form so as greatly to reduce its volume, both for transporting it to the point of use, in ship and/or road tankers, and to give trucks and buses an increased range from a given on-board fuel tank capacity. Elaborately insulated and consequently expensive tanks are required for holding LNG.
Moving from diesel to CNG or LNG fuelling usually brings ongoing fuel cost savings. Those savings come not from combustion efficiency improvements – where the diesel continues to reign supreme – but chiefly from more favourable fuel duty levels imposed by national governments keen to encourage NG use, for emission and/or oil import reduction reasons.
But adoption of NG as a truck or bus fuel is beset with numerous constraints. Very different engine technology is called for. The most popular NG engines are spark-ignited, 100% dedicated to gas fuelling and carry a massive initial on-cost. That can be hard to justify, especially when the resale value of the vehicle at the end of five or seven years is taken into account. Second-hand buyers have, to date, proved to be extremely wary of NG vehicles. Fuel availability away from home depots is a key issue and because of their much lower compression ratio than a diesel’s, those engines also lack torque performance.
The main shortcoming of GTL is one of production scale. For it to be competitive in price, production plants requiring investment comparable with that of large oil refineries are needed.
It is felt in some quarters that a more technically attractive use of NG, as an alternative to cryogenically liquefying it, is to convert it into an easily-handled synthetic fuel, able to be consumed by any regular diesel engine. The GTL (gas-to-liquid) Fischer-Tropsch catalytic process is now well proven. The end-product is virtually free of sulphur, making for very low noxious emissions. The main shortcoming of GTL is one of production scale. For it to be competitive in price, production plants requiring investment comparable with that of large oil refineries are needed.
But if, as predicted, future global oil price rises outstrip those for NG, then GTL will become a more viable proposition and, crucially, a more practical one when compared with LNG. In a decade or so, competition between LNG and GTL is likely to become a key issue for the truck and bus fuelling business.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Alan Bunting has a background in engineering, and has been writing on commercial vehicle and powertrain related topics since the 1960s. He has been an Automotive World contributor since 1996.
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