A Global Roadmap for Autogas

The main rationale for Autogas – from a societal perspective – is its environmental advantages. Because LPG is made up of chemically simple and pure hydrocarbons, it mixes easily with air allowing almost complete combustion. Consequently, Autogas out- performs gasoline and diesel and most other alternative fuels in the majority of studies comparing the environmental performance of conventional and alternative fuels that have been conducted around the world in recent years.¹ The results of these studies vary to some degree, according to the types of vehicles selected, the quality of the fuel, the types of emissions measured and the conditions under which they were carried out vary: actual vehicle emissions are highly dependent on vehicle technology and driving behaviour. But, overall, the picture is clear: switching to Autogas can bring major social, economic and environmental benefits

Numerous studies have shown that Autogas-related emissions of noxious and toxic air pollutants – both regulated and unregulated – are among the lowest of all the automotive fuels commercially available today. Autogas vehicles perform particularly well when a direct fuel injection system, which improves the anti-knock behaviour of the fuel and boosts fuel economy, is deployed.

The environmental performance of Autogas is particularly impressive with respect to regulated toxic gases, notably NOx and PM, or soot. Emissions of NOx – the most important of the regulated gases for air quality – from Autogas are much lower than from gasoline and, especially, diesel (Box 3). One of the key environmental advantages of Autogas over gasoline and, especially diesel, is the near-absence of PM emissions.

They are negligible for Autogas and very low for gasoline vehicles, but remain a major problem for diesel vehicles. Autogas emissions are comparatively even lower for cold starts, since gasoline needs to be enriched when the engine is cold due to its poor vaporisation characteristics at low temperatures. Since most city car trips involve very short distances, urban emissions from Autogas are generally much lower than from gasoline. The environmental advantages of Autogas are even bigger with respect to unregulated emissions, including air toxics such as aldehydes, benzene, toluene and xylene, poly-aromatic hydrocarbons, as well as smog-forming components and acidification potential (through mixes of NOx and sulphur dioxide).

NOx is a toxic air pollutant in its own right as well as the main cause of smog – a leading form of air pollution and a major public health problem. When nitrogen is released during fuel combustion it combines with oxygen atoms to create nitric oxide (NO), which combines again with oxygen to create nitrogen dioxide (NO2). Nitrogen dioxide and nitric oxide are referred to together as oxides of nitrogen, or NOx. NOx reacts with VOCs from industrial activities, vehicles and naturally occurring sources in the presence of sunlight to form photochemical smog – a cocktail of ground-level ozone and other toxic chemical compounds. Smog increases during the summer when solar radiation is highest, which is why this type of smog is commonly referred to as summer smog.

NOx harms human health in a variety of direct and indirect ways. NO2 is an irritant gas, which at high concentrations causes inflammation of the respiratory system. Ozone causes damage to lung tissue and reduces lung function, especially among children, the elderly and asthmatics. The nitric acid vapour and related particles formed when NOx reacts with ammonia, moisture and other compounds can penetrate deep into lung tissue, causing severe damage and even premature death. Inhaling such particles can cause or worsen respiratory diseases, such as emphysema or bronchitis, and can aggravate existing cardio-vascular disease. Smog also contributes to acid rain. NOx emissions also contribute directly and indirectly, through chemical reactions with other compounds in the atmosphere, to the greenhouse effect, accentuating climate change.

Evaporative and fugitive emissions of hydrocarbons from motor vehicles and refuelling facilities are also much less of a problem with Autogas than for conventional fuels and biofuels since it is used in gaseous form in sealed systems. Such emissions are known to make a substantial contribution to total VOC emissions. This is a particular problem with gasoline, due to its volatility. Because they have completely sealed fuel systems, Autogas vehicles and pumps have virtually zero evaporative emissions and fugitive emissions are normally limited to the very small release of gas when the fuelling coupling is attached and removed.

Switching to Autogas can also make a significant contribution to reducing greenhouse-gas emissions. With respect to CO2, Autogas performs better than gasoline and, according to some studies, emits less than diesel, when emissions are measured on a full fuel-cycle, or “well-to- wheels” (WTW), basis and when the LPG is sourced from natural gas processing plants. Autogas also compares well with other alternative fuels. A recent study suggests that well-to-wheel emissions for Autogas are generally quite similar to CNG because of the much higher emissions associated with the processing and transportation of natural gas. Biofuels, in principle, can achieve significantly lower greenhouse- gas emissions on a well-to-wheels basis as the feedstock is renewable. However, in practice, these reductions are often minimal, as they depend on the type of feedstock and the process used to produce the fuel, which is often highly energy-intensive. As a result, Autogas emissions on a WTW basis are often no higher than those from ethanol or biodiesel.

In the future, bioLPG used as Autogas could help reduce CO2 emissions from road transport even further. BioLPG is LPG derived from production processes that use renewable biomass as the feedstock, usually as a co-product. As such, net CO2 emissions from the production and use of bioLPG are zero.

The molecular structure of pure biopropane is identical to that of conventional pure propane produced from hydrocarbons, so can be blended into conventional LPG as a “drop-in” fuel or sold in a pure form. The main source of commercial supplies of bio-LPG at present is a plant in Rotterdam operated by the Finnish company, Neste, with the output sold to SHV Energy. But a number of other companies and organisations around the world are producing bioLPG, which could be marketed as such, or conducting research into advanced biofuels production processes, some of which involve the production of bio-LPG as a co-product or the principal output.