Q: What does the abbreviation CNG stand for?
A: CNG is the abbreviation for the term “compressed natural gas”. Compressors are used to compress natural gas so as to reduce its volume. This allows more energy to be transported and stored in a limited space. The compression is carried out at a pressure of about 200 bar. This increases the energy content per cubic metre of gas 200-fold.
Apart from the underground reservoirs of natural gas extracted, biogas can also be produced from renewable raw materials and agricultural waste and compressed to form CNG.
Q: How is CNG distributed to filling stations?
A: CNG filling stations source their fuel from the underground distribution grid which supplies households and businesses with natural gas. CNG does not therefore need to be transported by road or rail. The gas distribution grid in Germany alone has a total length of around 500 000 kilometres. This guarantees nationwide distribution of CNG.
Q: Natural gas is also a fossil fuel – are there “green” alternatives?
A: During the course of the energy transition, the share of biogas as a proportion of the overall consumption of gas for heating, for mobility and electricity consumption has gradually increased over the years. This guarantees certainty of supply and increases independence from imports. It also contributions to improving the carbon footprint. Biogas is produced from natural raw materials. The combustion of biogas only produces as much CO2 as was bound by the growth of the plants. Another carbon neutral alternative is provided by power-to-gas technology. Electrolysis can be used to split water into oxygen and hydrogen using renewable electricity generated from wind, water or solar power. The hydrogen – also compressed– can be mixed with natural gas and feed into the supply grid.
Q: Can biogas be filled directly into the tank of a CNG vehicle?
A: Biogas is produced by fermentation of natural raw materials. Generation of biogas is supplementary to and also an alternative to natural gas production. The most important common attribute: methane is the principal component and key energy source of natural gas and biogas. However, the proportion of methane is not constant. Biogas – like natural gas – therefore has to be refined before being fed into the supply grid. This process creates organic natural gas – an energy source that can be used for heating and driving without any problems.
Q: How safe are CNG power units in an automobile?
A: The tanks for CNG models are among the most robust and therefore the safest components in a vehicle, and are subject to extremely stringent safety checks (including by the German Technical Inspectorate (TÜV) and the German Automobile Association (ADAC)). After CNG tanks have been manufactured, each tank is individually tested to a maximum pressure of up to 300 bar. This exceeds the actual loads in practice. CNG at the pump is filled into the tank at a pressure of around 200 bar. The CNG tank is located in the area of the vehicle underbody and if an accident occurs, the tank is optimally protected. If severe damage occurs in an accident, safety valves also ensure targeted release, or respond to the effect of heat – e.g. if the vehicle catches fire – with controlled combustion of the gas reservoir and therefore prevent the hazard of an explosion.
Q: How many CNG vehicles are there on Germany’s roads?
A: According to the German Federal Motor Vehicle Transport Authority (KBA), 91 436 automobiles powered by CNG engines are licensed on Germany’s roads (status: 1. Jan. 2018).
Q: Which CNG vehicles does the Volkswagen Group supply?
A: Volkswagen has been integrating vehicles with CNG engines into its brand strategy for a long time now. The selection of models that can be powered by natural gas is continually growing. The following models are currently available (status: May 2017):
- Audi A3 Sportback g-tron
- Audi A4 Avant g-tron
- Audi A5 Sportback g-tron
- VW eco up!
- VW Caddy TGI BlueMotion
- VW Caddy Maxi TGI BlueMotion
- VW Golf TGI BlueMotion
- VW Golf Variant TGI BlueMotion
- VW Polo TGI
- SEAT Leon TGI
- SEAT Mii 1.0 Ecofuel
- SEAT Leon ST TGI
- SEAT Ibiza TGI
- ŠKODA Citigo G-TEC
- ŠKODA Octavia G-TEC
- ŠKODA Octavia Combi G-TEC
Q: Why is CNG measured in kilograms instead of in litres?
A: CNG is supplied at filling stations in compressed form (CNG = Compressed Natural Gas). It is pumped into the vehicle tank at a pressure of around 200 bar. This means that CNG at the filling station and in the vehicle is always in the gaseous state. At low pressure, the gas expands without the energy content important for the customer increasing. Because the volume could at least theoretically fluctuate depending on the compression intensity, CNG is measured in kilograms and not in litres in accordance with the German Calibration Act. This is because in contrast to volume, the weight always remains constant, irrespective of how much the CNG is compressed. Data in kilograms therefore provides the customer with a reliable unit for measuring the amount of energy that is received when filling the tank.
Q: How do you compare the energy content of 1 kilogram of CNG with 1 litre of petrol?
A: The energy content of one kilogram of CNG corresponds approximately to that of 1.3 litres of diesel fuel or 1.5 litres of premium petrol. Calculated differently: One kilogram of CNG has an energy content almost 50 percent higher than one litre of petrol – 13.3 kilowatt hours (kWh) compared with 8.6 kWh. One litre of diesel is equivalent to 9.9 kWh.
Q: How great are the savings for fuel costs?
A: Using CNG instead of petrol or diesel leads to a substantial decrease in fuel costs. One example: Anyone driving a ŠKODA Citigo G-TEC will pay 3.19 euros for every 100 kilometres at a CNG price of 1.10 euros per kilogram and an average consumption value of 2.9 kilograms. The comparable petrol engine version of this model generates fuel costs of 5.90 euros per 100 kilometres (at a price of 1.31 euros per litre of petrol).
Q: Where can I refuel my vehicle with CNG?
A: More than 900 public CNG filling stations are available in Germany.
Q: Is it possible to do something wrong when filling up with CNG?
A: The refuelling procedure is completely unproblematic with CNG. No adaptor or other accessories are necessary for refuelling. The dispenser is simply inserted and engaged with the tank nozzle of the vehicle. Both connectors are in conformity with a uniform European standard. Any operating error is therefore precluded. The actual filling procedure into the tank only commences after a correct connection has been made.
Q: What is the emission behaviour of CNG vehicles?
A: Current vehicles with a CNG power unit correspond as a minimum to the latest extremely rigorous Euro 6 exhaust gas standard. The fact that the fuel is already present in gaseous form makes metering and feeding into the combustion chambers easier and therefore ensures clean combustion. The engine’s CO2 emissions per kilometre are around 35 percent less than in the case of comparable models powered by petrol engines. The emissions of nitrogen oxide and hydrocarbons are as much as 87 and 67 percent less respectively. Furthermore, the exhaust gases generated during operation of a CNG vehicle contain virtually no fine dust.
Q: Is there a loss of performance in CNG vehicles?
A: No, vehicles with a CNG power unit have been designed by manufacturers for use of this type of fuel from the factory. Their power units are based on the engines developed for operation with spark-ignition fuel. They therefore also generate a comparable degree of driving fun as an equivalent petrol vehicle. Slight performance losses have to be anticipated only when retrofitting a CNG power unit owing to the necessary modifications to the engine.