Life Cycle Environmental Implications of the Use of Catalytic Converters in Vehicles Operating on Liquefied Petroleum Gas (LPG)

Liquefied petroleum gas (LPG), and natural gas (NG) are widely used as transport fuels in Australia, and indeed, some new vehicles are manufactured to run predominantly or entirely on LPG. Such fuels usually produce significantly lower carbon monoxide (CO) and hydrocarbon (HC) emissions than liquid fuels, and therefore the need for an exhaust catalyst in these vehicles is reduced. Although an exhaust catalyst provides near-complete abatement of HC and CO emissions (when fully functional), particulate heavy metals, such as platinum, rhodium and palladium are emitted during the utilisation stage. Furthermore, the manufacture of exhaust catalysts is energy intensive. This work details a life cycle assessment to determine whether it is environmentally beneficial to fit catalytic converters to vehicles which solely combust LPG, using data representative of common LPG passenger vehicles (taxis) in Australia. Surprisingly, it was found that the use of an exhaust catalyst in an LPG vehicle was only beneficial in reducing eutrophication, and detrimental in all other aspects. Therefore, if NOx emissions from LPG combustion can be reduced, there may be no net benefit in fitting LPG vehicles with an exhaust catalysts.