What low-emission fuel made its debuts decades ago yet still offers a highly-competitive alternative to other low-carbon energy sources? Gas, of course, and our expert says its benefits remains the same
Discussion of low-emission bus technologies has thus far examined new and emerging fields, but this column will give an overview of an ultra-low emission power source that is new to the UK, but which has been in use abroad from as early as 1935.
There are thousands of such buses in use in Europe, and hundreds of thousands of them worldwide. They are natural gas-fuelled, and they have practically no noxious or particulate emissions.
Developments in biomethane production and distribution via the national gas grid mean that renewable gas fuel is available UK-wide. It is carbon neutral, and in some cases it is carbon-negative.
Gas engines are as quiet as electric propulsion and the only exhaust treatment needed is a three-way oxy catalyst. Gas buses, fuelled with biomethane, satisfy all LCEB and OLEV requirements.
Gas engines are spark ignition, four-stroke Otto cycle units and very similar to petrol engines. Their performance, in terms of power and torque, is similar to or better than the equivalent diesel.
There is no unfamiliar technology to master in the operation and maintenance of the powertrain; only the fuel’s storage and delivery differs. Gas is stored in vehicle tanks at pressures of up to 200bar (2,900psi).
The tanks are of a well-tested and proven design, usually constructed from lightweight composite material, and they meet stringent safety requirements.
Gas is metered and sold by the kg via dispensers that look like diesel fuel pumps. 1kg of gas is approximately equivalent to one litre of diesel. It is compressed from the grid to the required pressure in an on-site station. There is never more than a day’s supply stored on-site; usually it is much less, and the gas is paid for monthly in arrears.
Current experience shows around a 20% operating cost saving for gas compared with diesel. The benefits are ultra-low emissions, quiet running and a carbon neutral or carbon negative environmental impact.
Future columns will look in more detail at biomethane production and distribution, the technology of the fuel and the buses, and will include some operator experience.
Our industry expert speaks with authority and can back up all of his facts, but what do you think? Email editorial@divcom.co.uk if you agree or disagree with him.
