Natural gas is now a very common fuel used in stationary
and some automotive diesels. It burns more cleanly than diesel
fuel, with very low emissions levels, and is often cheaper.
The gas is usually metered into the engine inlet manifold,
or directly into the engine cylinders in some cases. As with
a gasoline engine, a means of controlling the ignition of
the gas is required, either a spark ignition system, or small
quantity of diesel fuel injected to initiate the combustion.
Gas also presents a storage problem for mobile vehicles.
Natural gas is usually supplied either as liquefied natural
gas (LNG) requiring an insulated tank, or compressed natural
gas (CNG). Both require high pressure storage.
Other fuels such as biodiesel, made from oil-seed rape or other oil bearing seeds
and Liquid Petroleum Gas also offer some environmental benefits.