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The full form of CNG is Compressed Natural Gas. The fuel gas known as compressed natural gas (CNG) is mainly composed of methane (CH4) and is compressed to less than 1% of its volume at standard atmospheric pressure. It is typically distributed and stored in hard containers with spherical or cylindrical shapes at a pressure of 20–25 megapascals.
What is CNG?
Compressed natural gas, is clear, odorless, and non-corrosive. This indicates that CNG is not only more environmentally friendly for our naturally lush landscape, but it can also be used as a cost-effective substitute.
CNG, also known as “green fuel,” has been used successfully as a fuel in our transportation system for decades. CNG, is an alternative fossil fuel to gasoline, diesel, or LPG. In addition to being safer than other fuels in the case of a spill, CNG is a more environmentally friendly substitute for those fuels.
CNG History
Internal combustion engines were initially powered by gases. In the 1850s, France conducted the first compressed gas experiments. During World War I, natural gas was first used as a fuel for transportation. Ohio’s Columbia Natural Gas tested a CNG carrier in the 1960s.
The ship’s design failed due to the high cost of the pressure vessels, which were intended to carry compressed natural gas in vertical pressure bottles. Since then, efforts have been made to create a CNG carrier that is profitable.
For CNG ocean transportation, there are currently a number of competing designs. To keep costs competitive, each design suggests a different strategy for maximizing gas transport while utilizing as much off-the-shelf technology as feasible.
How is CNG Produced?
Compressed natural gas is a cost-effective and environmentally beneficial alternative to fuels like gasoline and diesel. It is produced by compressing a gas, primarily CH₄, to less than 1% of its initial volume, or the volume it occupies at STP (Standard Atmospheric Pressure). Drilling holes in rocks allows for the extraction of natural gas from subterranean deposits.
CNG Energy Density
At 53.6 MJ/kg, CNG has the same energy density as liquefied natural gas. Because it is not liquefied, its volumetric energy density, 9 MJ/L, is 25% that of diesel fuel and 42% that of LNG (22 MJ/L).
CNG Composition
It is the gaseous byproduct of petroleum and the first product to separate during the distillation process. CNG is non-toxic and has no taste or odor. It is comprised of up of 93.05% methane, nitrogen, propane, carbon dioxide, and trace amounts of ethane.
Uses of CNG
The Indian Supreme Court ruled that automobiles manufactured after 1995 would need to be powered by unleaded gasoline. CNG is used in modified petrol/internal combustion engine vehicles or in vehicles built specifically for CNG. Types of CNG vehicle configurations include:
- Dedicated: Runs only on CNG.
- Dual Fuel: Has a separate liquid fuel system to extend range.
- Bi-fuel: Can switch between CNG and another fuel (like petrol).
- Compressed Natural Gas can replace petrol, diesel, and LPG.
- CNG combustion emits fewer harmful gases compared to other fossil fuels.
- In case of a spill, natural gas poses less danger as it is lighter than air and disperses quickly.
It is possible to convert any existing gasoline-powered vehicle to a dual-fuel gasoline/Compressed Natural Gas vehicle. Authorized shops can complete the retrofitting, which includes installing electronics, a CNG injection system, plumbing, and a CNG cylinder.
Installation of a CNG conversion kit is typically reserved for vehicles that travel a lot of miles annually and can cost up to $8,000 for passenger cars and light trucks. In addition to being roughly 50% less expensive than gasoline, CNG produces up to 90% fewer emissions.
CNG in Locomotives
Many railroads use CNG locomotives. Prior to 2002, the US’s Napa Valley Wine Train successfully converted a diesel locomotive to run on compressed natural gas. This converted locomotive is currently the main locomotive of the Napa Valley Wine Train and was modified in May 2008 to use a computer-controlled fuel injection system.
Since 2005, Ferrocarril Central Andino in Peru has operated a CNG locomotive on a freight line. CNG locomotives are typically diesel-electric locomotives that have been modified to produce the electricity needed to run the traction motors using compressed natural gas generators rather than diesel generators.
CNG in Public and Commercial Transport
Due to high fuel prices and environmental concerns, CNG is widely used in:
- Auto-rickshaws
- Pickup trucks
- Transit buses
- School buses
- Trains
CNG in Natural Gas transport
Natural gas is transported by sea using CNG carrier ships over intermediate distances, particularly in situations where pipeline or LNG infrastructure is lacking. Undersea pipelines are frequently more economical for short distances, while LNG is frequently more economical for longer distances.
CNG Advantages
CNG offers several benefits compared to traditional fuels like petrol and diesel. Below are some key advantages of CNG:
- Compared to other vehicles powered by hydrocarbon fuels, natural gas vehicles require less maintenance.
- Because CNG fuel systems are sealed, fuel loss from spills or evaporation is avoided.
- Lubricating oils have a longer lifespan because CNG doesn’t contaminate or dilute crankcase oil.
- CNG mixes readily and uniformly in air because it is a gaseous fuel.
- Because of its high auto-ignition temperature (540 °C) and limited flammability range (5–15 percent), CNG is less likely to ignite on hot surfaces.
- Compared to gasoline-powered vehicles, CNG-powered vehicles are thought to be safer.
- Using CNG can help reduce greenhouse gas emissions because it emits less carbon dioxide. Nonetheless, natural gas leaks (from the fuel’s production and delivery as well as from its direct use) result in a rise in greenhouse gas emissions.
CNG Disadvantages
While CNG is a cleaner and cost-effective fuel option, it comes with certain limitations that may affect its widespread adoption. Below are some of the disadvantages to consider:
- CNG requires more storage space than petrol because it is stored as a compressed gas, not a liquid.
- For each GGE (gasoline gallon equivalent), CNG needs more volume than petrol.
- In converted vehicles, CNG cylinders are usually placed in the trunk or bed of a pickup truck, reducing available space. This issue is resolved in factory-built Compressed Natural Gas cars by setting CNG cylinders under the body of the vehicle, freeing up trunk space. Examples of such vehicles:
- Fiat Multipla
- New Fiat Panda
- Volkswagen Touran Ecofuel na Volkswagen Caddy Ecofuel
- Chevy Taxi (sold in countries like Peru)
- In buses, cylinders are often installed on the roof.
- Roof installations may require structural modifications for safety and balance.
- Unburned methane leakage is a major issue in natural gas systems.
- Methane (CH₄), the main component of CNG, is a strong greenhouse gas. It is over 100 times more powerful than carbon dioxide in trapping heat over a short period.
- Even small leaks can significantly impact climate change, making methane control essential.
Challenges in CNG Adoption
The main barrier to widespread CNG use is the cost and placement of fuel storage cylinders. Public and municipal vehicles were early adopters because:
- They can recover the cost faster.
- CNG is cheaper for large fleet operations.
CNG Growth and Technological Progress
Global CNG vehicle numbers have grown at around 30% per year. Due to this growth, the cost of CNG storage cylinders has come down significantly. For vehicle conversions, CNG Type 1 and Type 2 cylinders are now more reasonably priced in many countries.
CNG Codes and Standards
Another obstacle to NGV market penetration is the absence of uniform codes and standards among international jurisdictions. A technical committee of the International Organization for Standardization is currently developing a standard for vehicle natural gas fueling stations.
Natural gas vehicles have an outstanding safety record worldwide, even in the absence of standardized international regulations. Current international standards include ISO 15500-9:2012, which outlines requirements and tests for the pressure regulator, and ISO 14469-2:2007, which covers CNG vehicle nozzles and receptacles.
Natural gas vehicle safety requirements in the US are outlined in the NFPA 52 code, which is published by the National Fire Protection Association.
CNG Comparison with Other Natural Gas Fuels
The table below summarizes the key differences between CNG, LNG, ANG, and HCNG in terms of storage, cost, energy density, and applications.
| Feature | CNG (Compressed Natural Gas) | LNG (Liquefied Natural Gas) | ANG (Adsorbed Natural Gas) | HCNG (Hydrogen-CNG Blend) |
| State | Supercritical fluid (high pressure) | Liquid (cryogenic) | Adsorbed gas (sponge-like materials) | Gas mixture (CNG + Hydrogen) |
| Storage Pressure | 205–275 bar (3000–4000 psi) | Near-ambient pressure (~1 bar) | ~35 bar (500 psi) | Similar to CNG (200+ bar) |
| Storage Temperature | Ambient (~25°C) | Cryogenic (-162°C) | Ambient (~25°C) | Ambient (~25°C) |
| Energy Density | Lower than LNG | Higher than CNG | Similar or greater than CNG | Lower than CNG (due to H₂ addition) |
| Production Cost | Lower (no cryogenic cooling needed) | Higher (requires liquefaction & cryogenic storage) | Moderate (requires adsorbent materials) | Higher (requires hydrogen blending) |
| Storage Requirements | Heavy, high-pressure tanks | Expensive cryogenic tanks | Lighter, low-pressure tanks | Similar to CNG tanks |
| Refueling Source | Requires high-pressure compression | Requires LNG infrastructure | Can use natural gas pipelines directly | Requires hydrogen blending |
| Transportation Use | Short-distance distribution | Long-distance (ships, trains, pipelines) | Emerging technology (limited use) | Experimental (improves combustion efficiency) |
| Advantages | Lower storage cost and Mature technology | High energy density and Efficient for transport | Lower pressure and Lighter tanks | Faster flame speed and Lower emissions |
| Disadvantages | Large storage volume and High-pressure risks | High production cost and Boil-off losses | Limited adsorbent capacity and Developing tech | Reduced energy density |
CNG Full Form FAQs
Is CNG better than petrol?
When compared to petrol, compressed natural gas, or CNG, is a far cleaner fuel option.
Is it safe to drive a CNG vehicle?
In general, CNG (Compressed Natural Gas) cars are regarded as safe, particularly when contrasted with older, less sophisticated automobiles.
What are the drawbacks of CNG?
Performance Lag: Perform worse than cars that run on gasoline and diesel.
Does CNG catch fire?
Compressed natural gas has the potential to ignite. This fuel contains mostly a flammable gas (methane).
