LPG stands for ‘liquified petroleum gas’ and is also known as ‘autogas’ in some markets. It consists of a mixture of propane (C3H8) and butane (C4H10) and has very few impurities in it.
It is energy-dense and therefore does not require a large tank, which makes it suitable for vehicles such as forklift trucks and passenger cars. It can also be used in conjunction with diesel on trucks and buses which have been converted to run on dual fuels.
Engines running on LPG can be lean-burn or stoichiometric. Lean burn engines can be fitted with two-way catalytic converters whilst stoichiometric engines enable the use of three-way catalytic converters.
Because LPG engines run quite hot, NOx emissions can be high so three-way catalytic converters have to be specified with this in mind. Another consideration is that lambda control on stoichiometric LPG engines is not always very precise, so a catalyst which can give high efficiency in a wide lambda window is a benefit.