CNG – the sustainable alternative
CNG vehicles combine the comfort and suitability for everyday use of conventional petrol-driven models with lots of advantages that primarily relate to the issue of sustainability. CNG has a higher energy density and is conducted to the engine in a homogeneous gaseous state. It is therefore more economically efficient than petrol or diesel and undergoes a particularly clean burn. The noise and particularly the emissions of harmful substances are significantly lower than when conventional fuels are used. This applies to CO2, nitrogen oxide and fine dust. Another factor is that the environmental benefit of CNG will continue to grow over the medium and long term. This will be ensured by the enhanced admixture of biogas and synthetic natural gas. The use of these renewable energy sources comprised of renewable natural raw materials means that the engine of a CNG vehicle only releases as much CO2 as was previously bound during the growth of the plants. CNG therefore has the potential to become a climate-neutral energy source for individual mobility.
Out of all fossil fuels, CNG – or its main constituent element of natural gas – is the fuel that causes the least CO2 emissions in the course of its combustion. This is due to its chemical composition. In the chain of molecules, the ratio between carbon (C) and hydrogen (H) atoms is about 50 percent lower than in the case of petrol or diesel. As a result, significantly lower volumes of carbon dioxide (CO2) and a higher proportion of water (H2O) are released during combustion with the addition of oxygen (O2).
If CNG comprises pure natural gas, the CO2 emissions caused during driving are around 18 to 25 percent lower than with engines running on petrol. The addition of biogas enables the CO2 footprint of CNG mobility to be further optimised. This is because the use of biogas does not contribute to the greenhouse effect. On the basis of the average proportion of biogas in CNG amounting to some 20 percent and in direct comparison with modern Euro 6 vehicles operating on petrol or diesel, the CO2 values are therefore already 35 and 23 percent lower respectively. Furthermore, the nitrogen oxide emissions can be reduced when drivers move to CNG: by 67 percent compared with petrol vehicles and by as much as 96 percent compared with diesel vehicles. The CNG exhaust gases also have lower fine-dust components. They are 99 percent lower compared with petrol and 50 percent less by comparison with diesel.
According to a study commissioned by the European Natural Gas Vehicle Association (NGVA), the total greenhouse gas emissions are significantly reduced by using CNG as a fuel, particularly in the countries of Central Europe. The reason for this lies in the comparatively low upstream emissions. Thanks to advanced technology, the treatment and distribution of natural gas produces fewer harmful substances than in other regions of the world.
Alongside the potential of CNG use for passenger automobiles, the study published by the NGVA also looked at the potential greenhouse gas savings when transporting goods on the road. According to this study, trucks powered by CNG could generate up to 18 percent fewer emissions by comparison with diesel. The greenhouse gas savings are between 16 and 22 percent if trucks are powered by LNG (Liquified Natural Gas).
A further increase in the proportion of biogas and synthetic natural gas above the current value achieved would allow the sustainability of CNG to be gradually increased. If biogas were used exclusively, this would entail a CO2 reduction of 97 percent in road traffic – less a residual proportion of upstream emissions.
Energy crops like maize and sugar beet along with biological waste and agricultural residues are used to generate biogas in Germany. Fermentation of these substances in biogas plants generates gas containing methane which has the same properties as natural gas after it has been treated. The cultivation of energy crops provides a yield per hectare of land sufficient to supply five CNG vehicles for a year (distance travelled: in each case around 15 000 km/year) if they are run on pure biogas. This means that the area efficiency for generation of biogas based on land use is higher than that of fuels generated from other fuels derived from renewable materials.
An area of land measuring around two million hectares in Germany is currently used for cultivating energy plants. By way of comparison, an area of land around five times higher is required to generate feedstock for keeping cattle. Generally speaking, the biogas association – Fachverband Biogas e. V. – continues to perceive significant scope for expanding energy extraction from renewable raw materials. The association reported that this scope is available without any additional arable land for energy plants since in many regions the fermentable green waste already available is not yet being used to generate biogas. A further side effect could be a contribution to protecting the groundwater – for example by making use of liquid manure through fermentation in biogas plants. If this waste material is only spread on the fields once it has fermented, it is easier for the plants growing there to absorb the nutrients. The continuous increase in the proportion of biogas in CNG is therefore associated with a gradual expansion of generating capacities while at the same time developing the technology further and enhancing production efficiency.
Independently of this, owners of CNG vehicles can already enjoy a virtually climate-neutral form of mobility by filling up with pure organic natural gas. This is supplied nationwide at 125 filling stations. Automobile manufacturer Audi is also taking account of the awareness of its customers for sustainability with an additional offering to permit CO2 neutral mobility. A special billing procedure ensures that the CNG volume consumed in an Audi g-tron model is registered and a corresponding amount of synthetic natural gas is produced in a power-to-gas plant operated by the automobile manufacturer.