The big picture

Contrary to common belief, airborne emissions from road vehicles come not just from the exhaust pipe. The zero-emissions vehicle, which is currently been hyped, is actually a myth. Neither hydrogen, nor biofuels nor the pure battery-powered electric vehicles are genuinely emissions-free, as in having zero impact on the environment. When assessing the impact of a fuel on the environment, especially its potential to contribute to climate change, and when comparing alternative fuels like Autogas to conventional fuels, one needs to take into account all aspects of the supply of the fuel, as well as how much of it is consumed in the vehicle.

LPG is a by-product of the extraction of petroleum and natural gas, of the refining of petroleum products and the production of synthetic liquid fuels, including – in some cases – those from renewable sources. Supply of LPG is set to continue to expand in the coming years, particularly with increased production of liquefied natural gas (LNG), as the separation of methane from other products contained in the natural gas stream is performed more easily in the liquefaction process. The portability and ease of transportation of LPG as a commodity fuel also favours the development of the market. The fuel’s environmental advantages provide a further reason to be confident about the prospects for availability for LPG in general and Autogas in particular.

Providing information on the benefits of using Autogas isn’t the end of the story. A holistic comparison with other fuels, taking all their different attributes into account provides a solid basis for evaluation. Given the practical constraints on a number of alternative transport fuels, it makes sense to compare the environmental characteristics of Autogas with those of its close relative: compressed natural gas (CNG).

Comparative research

In an attempt to set the record straight about how well Autogas and CNG – the two most widely used alternative fuels worldwide – compare in reality, Professor Thomas Heinze of the University of Applied Sciences in Saarland, has carried out a detailed benchmarking analysis taking account of emissions at all stages of the supply chain, including production, transportation and final combustion of the fuel. While tail-pipe emissions data suggest that the reductions in emissions of carbon dioxide (CO2) compared with conventional fuels (gasoline and diesel) are typically about 50% higher for CNG than for Autogas, his analysis reveals that the actual emissions reductions are generally quite similar for both fuels.

“Natural gas companies have always been pointing to lab data in preaching to politicians that natural gas is the cleanest fuel for spark-ignition engines. I want to prove that the reality is different from the pure heating value comparison, and that Autogas is one of the cleanest of all realistic options”, says Professor Heinze.

In his study, “Well-To-Wheel (WTW) Analysis of Gas Vehicles”, published in 2010 and updated in 2012, he compares Autogas and CNG used in spark-ignition engines, using gasoline as a baseline. A well-to-wheel analysis represents an analytical framework to assess the global warming potential of a fuel taking into consideration not just the tail-pipe emissions from the vehicle but also the emissions from the energy consumed along the entire production and transport chain, including the delivery of the fuel to service stations, as well as other emissions such as leakages of gas from pipelines into the atmosphere.

The Facts and Figures

A simple heating-value comparison suggests that tail-pipe emissions of CO2 are 19% lower for CNG than for gasoline; the equivalent reduction in emissions for Autogas is 9.2%. Professor Heinze suggests that once you factor in the energy consumed in piping natural gas over long distances, compression at the station, as well as the actual tail-pipe emissions, CNG’s environmental profile is less pronounced; in some cases, its carbon performance is bettered by that of LPG. An important but often forgotten factor in determining tail-pipe emissions is the weight of the vehicle. The average CNG system weighs in at around 150 kg, whereas an Autogas system adds only 35-70 kg to the total weight of a standard passenger car. Additional weight means that more energy needs to be consumed to move the vehicle along the road. For this reason, differences in vehicle emissions were studied across a range of vehicles by applying average fuel consumption data (as provided by the manufacturer) from all new gas-fuelled cars available in Germany in 2010.

Beyond certain ranges the compression process used in long-distance pipeline transportation of natural gas consumes more energy than shipping and road transport. There is also the possibility of distribution losses from NG pipelines to consider. The study finds that the transportation distance at which emissions from CNG exceed those of Autogas is a mere 2 350 km. At this distance, CNG’s total environmental performance in terms of a reduced CO2 emissions equivalent in comparison with gasoline drops to 15.2% – equal to that of Autogas – only slightly lower than 18% in the case of gas supplied from the North Sea. At greater distances, CNG’s environmental performance is inferior to that of Autogas. At gas-pipeline distances of around 7 000 km, which would equate to fields in far eastern Russia, CNG manages to maintain a meagre 2% CO2 advantage over gasoline.

As the supply of CNG from near sources is not unlimited and the reduction potential of the entire mix is thus limited by the pipeline distances, both gaseous fuels ideally supplement each other to maintain the CO2-advantage for alternative fuels in Western Europe.

Autogas carbon emissions are at least on a par with CNG in Europe!

The environmental performance of fuels can only be assessed by looking at the whole picture which includes transportation as well as combustion. The reality of logistics, once factored in, dramatically changes the conclusion we get from chemical material data and lab experiments. About 60 % of the LPG consumed in Europe is sourced from North Sea terminals and 40 % from refineries within Europe, making it a truly local energy source.

Based on well-to-wheel analysis for our market, Autogas is actually at least on a par with CNG with respect to well-to-wheel emissions. It thus compares very favourably to CNG and – given Autogas’ other advantages – represents the only other alternative fuel to be taken seriously in Western Europe.

To find out more about the results of Professor Heinze’s comparative well-to-wheels study of CNG and Autogas, please do not hesitate to contact Alex by email at: A.Stoehr@dvfg.de.