CNG – what is compressed natural gas? Its importance in transport

With the growing importance of climate protection and stricter requirements for transport emissions, the automotive industry is now facing the need for a profound transformation. The introduction of clean transport zones, rising prices of traditional fuels and regulatory requirements are prompting transport operators to seek more sustainable and cost-effective solutions.

One fuel that is gaining in importance is CNG, or compressed natural gas, which is becoming a viable alternative to diesel, LPG or electric vehicles, especially in urban and regional transport.

In this article, we discuss in detail what CNG is, what its properties are, where it is used and when it may be the most advantageous choice – not only for the environment, but also for your wallet.

What is CNG?

CNG (Compressed Natural Gas) is a fuel produced by compressing naturally occurring natural gas – mainly methane (CH₄) – to a pressure of 200–250 bar. Importantly, this gas does not change its state of aggregation. Unlike LNG, it remains in gaseous form, but with increased density.

CNG is ideal as a fuel for vehicles, from city buses to light commercial vehicles. Its use in road transport is in line with global strategies to reduce greenhouse gas emissions and promote alternative energy sources.

Interestingly, CNG is the same gas that is supplied to homes for heating and cooking. In automotive applications, however, it is thoroughly purified and compressed, then transported to CNG filling stations as a ready-to-use fuel for vehicle engines.

Read also: LNG – what is liquefied natural gas? Its importance in transport >>>

Composition and properties of CNG

Compressed natural gas consists mainly of methane – its content reaches up to 98%. For this reason, CNG has a high energy value, which is approximately 50 MJ/kg. The gas also contains small amounts of other compounds, such as nitrogen, carbon dioxide, ethane and propane.

CNG is colourless, odourless and non-toxic, which is why an odorant – a characteristic odour substance that enables quick detection of a possible leak – is added to it for safety reasons. One of the advantages of using CNG in the automotive industry is the fact that in the event of a leak, the gas escapes vertically upwards, without forming dangerous puddles, as is the case with petrol or LPG.

CNG has a high auto-ignition temperature – as high as 540°C – so it is a non-flammable fuel and stable in terms of safety. It also does not cause corrosion of the fuel system, which translates into lower wear and tear on consumable parts and less frequent visits to the service station. In addition, its high octane rating (110–130) ensures high resistance to knocking and smooth engine operation.

CNG storage requires appropriate conditions – the gas is stored in special, reinforced tanks made of steel or composites. This makes the cylinders resistant to mechanical damage even under difficult operating conditions.

Advantages of CNG (compressed natural gas) in transport

Compressed natural gas (CNG) is currently gaining popularity, and for good reason. In transport – especially urban, fleet and municipal transport – it stands out from other types of fuel, offering a number of measurable benefits.

Low exhaust emissions

Vehicles powered by compressed natural gas emit significantly fewer harmful substances than conventional combustion engines. Their use is associated with:

• a reduction in carbon dioxide (CO₂) emissions by up to 20-25% compared to diesel,
• a 70-90% reduction in nitrogen oxides (NOx),
• and an almost complete elimination of particulate matter (PM) – up to 99%.

What does this mean in practice? These parameters mean that CNG vehicles meet even the most stringent emission standards (Euro VI/6) and can travel without restriction in low emission zones (LEZ), which are rapidly expanding in Europe.

More about low emission zones: Ultra Low Emission Zone and other low emission zones in Europe >>>

Lower operating costs

CNG prices can be volatile, but even at slightly higher levels, they can still be competitive with diesel or petrol.

Maintenance costs are also lower – CNG combustion is cleaner than liquid fuels, which translates into lower oil consumption and longer component life. The absence of deposits and soot in the exhaust system has a positive effect on performance and reduces the need for costly repairs to DPF or EGR filters.

Quieter engine operation

Natural gas engines run noticeably quieter than their diesel counterparts. The difference can be as much as 3-5 dB, which in urban conditions translates into a real improvement in the quality of life for residents and drivers.

In night-time or municipal transport, e.g. when emptying waste containers, lower noise levels are a major advantage, and in the case of delivery vehicle fleets, they improve the comfort of everyday work. This is an aspect that has a significant long-term impact on the quality of the urban environment.

High safety

CNG is one of the safest fuels available on the market. As already mentioned, thanks to its very high auto-ignition temperature (540°C), the way the gas evaporates upwards in the event of a leak, and modern tank and valve safety systems, the risk of ignition or explosion is minimal. This makes compressed natural gas ideal for use in fleet, municipal and urban vehicles, where safety is of paramount importance.

The use of CNG in transport – where does it work best?

China, Iran and India are among the world leaders in the number of natural gas-powered vehicles, but fuels such as CNG are also becoming a popular solution in our European market. Why? Because they work well when ecology, economy and reliability matter – and these are increasingly valued qualities. Let’s take a look at the areas of transport where compressed natural gas is currently used in practice.

Urban and municipal transport

One of the first and largest consumers of CNG is public transport companies. CNG-powered buses run on the streets of many cities, offering lower noise levels, greater environmental protection and savings (compared to diesel vehicles). The same is true for refuse collection vehicles and other technical vehicles that operate in city centres – where strict environmental standards apply.

Last mile logistics and urban deliveries

In cities where online commerce and express delivery services are growing rapidly, CNG is becoming an excellent solution for courier and e-commerce companies as an alternative to diesel. Not only does it reduce fuel costs and allow unrestricted access to low-emission zones, but it also does not generate noise during night-time deliveries.

Another advantage is the ability to refuel quickly – in cities where CNG stations are more readily available, fuel logistics are practically non-existent. Although CNG also works well for deliveries in smaller towns and rural areas, the lack of infrastructure there may require support in the form of a dedicated refuelling station or more careful route planning.

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Light and fleet transport

Companies with fleets of delivery, service or representative vehicles are increasingly opting for CNG installation at the vehicle purchase stage. This is due to benefits such as:

• tax breaks or exemptions from fees in certain cities and regions,
• greater control over fuel costs,
• an eco-friendly image, which is becoming increasingly important to customers and public institutions.

In addition, with high mileage, the return on investment (ROI) in compressed natural gas vehicles can bring significant benefits, especially when the company has its own refuelling infrastructure.

In summary, CNG works best when vehicles are heavily used and the refuelling infrastructure is well planned. Under such conditions, it is not only a more environmentally friendly solution, but also an investment with real potential for return. It is also worth mentioning that, in addition to road transport, CNG is increasingly being used in coastal, ferry and port shipping. Compressed natural gas is thus becoming a versatile low-emission fuel used in various modes of transport.

Refuelling with CNG step by step

Refuelling with CNG may seem complicated at first glance. However, the procedure is intuitive and safe, as long as you follow a few basic rules.

How to refuel with CNG?

1. Stop the vehicle in the designated area and secure it against movement.
2. Turn off the engine and electrical devices, including the radio and mobile phone. Turn off the lights.
3. Read the available instructions and signage – some steps may vary depending on the station.
4. Make sure you do not see any damage or leaks in the refuelling system – if you have any doubts, move away and contact the station staff.
5. Connect the nozzle of the dispenser to the refuelling valve and follow the instructions. The connection must be tight and securely locked.
6. Start refuelling – the fuel flows into the tank under high pressure. The system controls this process automatically.
7. Disconnect the nozzle only after refuelling is complete and secure the valve with a protective cap.

Caution! It is recommended to wear gloves and safety goggles.

Importantly, for safety reasons, CNG refuelling station dispensers are equipped with:

• automatic gas shut-off systems when a leak is detected,
• breakaway couplings to prevent the hose from being torn out if the vehicle accidentally drives away,
• temperature and pressure sensors that constantly monitor the refuelling process.

CNG refuelling usually takes 3-5 minutes at fast-fill CNG refuelling stations, which is the same as refuelling with petrol or diesel. In the case of slow-fill stations, e.g. at fleet bases, refuelling can take from several dozen minutes to several hours and usually takes place at night when the vehicles are not in use.

Comparison of CNG, LNG and LPG

The table below shows the most important differences between the three popular types of gaseous fuels: CNG, LNG and LPG.

FEATURE	CNG (compressed natural gas)	LNG (liquefied natural gas)	LPG (liquefied petroleum gas)
Main component	Methane (CH₄): ~95–98%	Methane (CH₄): ~95–98%	Propane (C₃H₈) and butane (C₄H₁₀)
State of matter	Gas	Liquid	Liquid
Additional conditions	Compressed at a pressure of 200–250 bar	-162°C (cryogenic conditions)	Stored at ambient temperature, under moderate pressure of 5–10 bar
Energy density	Average	High	High
Type of vehicles	Urban transport, municipal transport, light delivery vehicles	Mainly heavy goods vehicles for long-distance routes	Passenger cars, delivery vehicles, some heavy goods vehicles
Safety in case of leakage	Escapes upwards, does not form puddles	Risk of freezing on contact with liquid, evaporates quickly	After evaporation, it settles and accumulates on the ground – forms flammable mixtures
Exhaust emissions	Very low (low CO₂, NOx, PM emissions)	Similar to CNG	Higher than CNG, but lower than diesel fuel
Application	Urban and local transport	Long-distance transport	Widely used in passenger cars in Europe
Comparison with diesel	Quieter, cleaner	Quieter, longer range	Cheaper, more readily available

Summary

In recent years, CNG, or compressed natural gas, has been gaining importance as a viable alternative to traditional fuels, especially in urban and fleet transport. It is characterised by low CO₂, particulate matter and nitrogen oxide emissions, quieter engine operation, high safety levels and operating savings.

Although the cost of installing or purchasing a CNG vehicle may be higher, in many cases the investment pays off, especially with high mileage and good refuelling infrastructure. Additional benefits, such as tax breaks or exemptions from LEZ charges, increase the attractiveness of this type of fuel.

Compressed natural gas is therefore not a passing trend, but a conscious choice made by many companies looking to save money and reduce the environmental impact of their transport operations.

Frequently asked questions (FAQ)

Is CNG an alternative fuel?

Yes, CNG (compressed natural gas) is classified as an alternative fuel – alongside biofuels, LPG, LNG and electricity. Its main advantage is lower emissions and less impact on the environment than petroleum-based fuels.

How does CNG differ from LPG?

CNG (compressed natural gas) consists mainly of methane and is stored under high pressure in gaseous form. LPG (liquefied petroleum gas) is a mixture of propane and butane, stored as a liquid under lower pressure. Another key difference is their behaviour in the event of a leak – CNG is lighter than air and rises, while LPG sinks and can form flammable mixtures near the ground.