Compressed natural gas (CNG) is a fuel gas produced from gasoline consisting primarily of methane (CH4) compressed to less than 1% of the volume it occupies at normal atmospheric pressure. It is stored and distributed in rigid containers at pressures of 20-25 MPa (2,900-3,600 psi), usually in cylindrical or spherical form.
CNG is used in conventional gasoline/IC vehicles that have been modified or in vehicles made specifically to use CNG: standalone (custom), with separate liquid fuel systems for extended range (dual fuel), or in conjunction with each other fuel (bi-fuel).
Can be used as a substitute for gasoline (petrol), diesel, and liquefied petroleum gas (LPG). When burning CNG, fewer unwanted gases are produced compared to the above-mentioned fuels. Compared to other fuels, natural gas is less hazardous in the event of a spill as it is lighter than air and spreads quickly if released. Biomethane – biogas purified from anaerobic digestion or landfill – can be used.
The cost and location of fuel storage tanks are the main barriers to the wider/rapid adoption of CNG as a fuel. This is another reason why cities and public transport vehicles are the most visible early adopters, as they can return the money invested in new (and usually cheaper) fuels faster.
Despite these circumstances, the number of CNG vehicles worldwide continues to increase (30 percent per year). As a result of the continued growth of the industry, the cost of these fuel storage cylinders has now been lowered to a much more affordable level. Especially for Type 1 and Type 2 CNG cylinders, many countries are capable of producing reliable and cost-effective conversion cylinders.
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Energy density
At 53.6 MJ/kg, the energy density of CNG corresponds to that of liquefied natural gas. The mass-energy density of 9 MJ/L is 42 percent of LNG (22 MJ/L) because it is not liquefied, and 25 percent of diesel.
History
Gas provides the basic fuel for internal combustion engines. The first experiments with compressed gases took place in France in the 1850s. Natural gas first became a transportation fuel during World War I. In the 1960s, Columbia Natural Gas of Ohio tested a CNG tanker. The ship will transport compressed natural gas in vertical cylinders.
However, this design failed due to the high cost of the pressure vessel. Since then, there have been several attempts to develop commercially viable CNG carriers. Several competing CNG designs for marine transportation have emerged over the last five years. Each design offers a unique approach to optimizing gas transportation while utilizing as much of the available technology as possible to maintain cost competitiveness.
Uses
Motor vehicles
Globally, there were 14.8 million natural gas (NGV) vehicles in 2011, mostly in Iran (4.07 million), Pakistan (2.85 million), Argentina (2.07 million), and Brazil (1.7 million). million) and India (1.1 million). Asia-Pacific leads with 5.7 million NGVs, followed by Latin America with nearly four million vehicles.
Several car and vehicle manufacturers such as Fiat, Opel/General Motors, Peugeot, Volkswagen, Toyota, Honda, Maruti Suzuki, Hyundai, Tata Motors, and others sell dual fuel vehicles. In 2006, the Fiat Siena Tetrafuel was launched in the Brazilian market, equipped with a 1.4 liter FIRE engine that uses E100, E25 (Brazilian standard gasoline), ethanol, and CNG.
Any existing gasoline-fueled vehicle can be converted into a gasoline/CNG dual-fuel vehicle. Authorized workshops can perform the conversion, which includes the installation of CNG cylinders, piping, CNG injection systems, and electronics. The cost of installing a CNG conversion kit can often be as high as $8,000 for cars and light trucks and is typically reserved for vehicles that drive many miles each year. CNG costs about 50% less than gasoline and produces up to 90% fewer emissions than gasoline.
Locomotives
CNG locomotives are operated by several railway lines. The Napa Valley Wine Train was successful in converting diesel locomotives to CNG before 2002.[9] This rebuilt locomotive was upgraded in May 2008 to use a computer-controlled fuel injection system and is now the main locomotive on the Napa Valley Wine Train. Ferrocarril Central Andino in Peru has been operating CNG locomotives since 2005.
CNG locomotives are typically diesel-electric locomotives that have been converted to use a compressed natural gas generator instead of a diesel generator to generate electricity that drives the traction motor. Some CNG locomotives can selectively fire their cylinders only when electricity is needed, theoretically giving them greater fuel efficiency than traditional diesel engines. It is also cheaper than gasoline or diesel.
Natural gas transport
It is used to transport natural gas by sea using medium-haul CNG carriers, especially when pipeline or LNG infrastructure is not available. Subsea pipelines are often cheaper over short distances, and LNG is often cheaper over longer distances.
Advantages
- Gas-fueled vehicles have lower maintenance costs than other hydrocarbon vehicles.
- Its fuel system is sealed to prevent loss of fuel through spills or vapors.
- Longer lubricating oil life because it does not contaminate or dilute crankcase oil.
- As a gaseous fuel, CNG mixes easily and evenly with air.
- CNG is less likely to ignite on hot surfaces because it has a high auto-ignition temperature (540 °C) and a narrow range (5-15 percent) of flammability.
- CNG-powered vehicles are considered safer than gasoline-powered vehicles.
- Less pollutant and more efficient:
- During combustion, CNG releases significantly fewer pollutants directly than gasoline or oil (e.g. unburned hydrocarbons (UHC), carbon monoxide (CO), nitrogen oxides (NOX), sulfur oxides (SOx), and PM (particles)). For example, an engine running 100 km on gasoline produces 22 kilograms of CO2, while the same distance on CNG produces only 16.3 kilograms of CO2.
- The life cycle of greenhouse gas emissions from compressed CNG natural gas from the California pipeline is defined by CARB (California Air Resources Board) as a value of 67.70 grams of CO2 equivalent per megajoule (gCO2e/MJ), about 28 percent lower than the average fuel gasoline in this market (95.86 gCO2e/MJ).
- CNG produced from landfill biogas has the lowest GHG emissions of all the fuels analyzed, according to CARB, with a value of 11.26 gCO2e/MJ (more than 88 percent lower than conventional gasoline) in the Low Carbon Fuel Standard applicable to January 12, 2010.
- Due to lower carbon emissions, switching to CNG can help reduce greenhouse gas emissions.[12] However, natural gas leaks (both in direct use and in the manufacture and delivery of fuels) mean increased greenhouse gas emissions. CNG’s ability to reduce greenhouse gas emissions throughout the fuel’s life cycle depends on the source of the natural gas and the fuel it replaces.
Drawbacks
CNG-powered vehicles require more fuel storage space than traditional gasoline-powered vehicles. Because it is a compressed gas and not a liquid like gasoline, CNG takes up more space for each GGE (Gasoline Gallon Equivalent). However, the cylinders used to store CNG occupy space in the trunk of a car or in the back of a pickup truck that has been converted to CNG.
This problem has been solved in factory CNG vehicles where the cylinder is mounted under the vehicle body and the trunk is left empty, e.g. B. Fiat Multipla, New Fiat Panda, Volkswagen Touran Ecofuel, Volkswagen Caddy Ecofuel, Chevy Taxi are sold in countries like Peru. Another option is a roof mount (typical for buses), but this may require structural modifications. In 2014 tests (by the Danish Institute of Technology) Euro6 heavy vehicles with CNG and diesel showed that CNG had higher fuel consumption.
The leakage of compressed natural gas into the environment “from wells to wheels” is a recognized contributor to climate change. According to a study by the Environmental Defense Fund and its partners, “Assuming EPA leak rate estimates, vehicles using compressed natural gas are not a viable strategy for mitigating climate change due to methane leaks from natural gas production, delivery infrastructure.
The release of unburned methane as natural gas is a significant problem because methane, a major component of natural gas, is a potent and short-lived greenhouse gas. It is more than 100 times more powerful at capturing energy than carbon dioxide (CO2), the main driver of human-caused climate change. When conversion to carbon dioxide over time is taken into account, the impact on an integrated weight basis is 84 times greater at 20 years and 28 times greater at 100 years, according to the Environmental Defense Fund’s Impact of methane emissions report.”
Comparison with other natural gas fuels
Compressed natural gas is often confused with LNG (Liquified Natural Gas). Both are stored in the form of natural gas. The main difference is that CNG is stored at ambient temperature and high pressure, whereas LNG is stored at low temperature and pressure close to the environment. Under the respective storage conditions, LNG is a liquid and CNG is a supercritical fluid.
It has lower production and storage costs than LNG because it does not require refrigeration processes and expensive cryogenic tanks. However, it requires a much larger volume to store the energy equivalent of gasoline and uses very high pressures (3000 to 4000 psi or 205 to 275 bar). As a result, LNG is often used to transport natural gas over long distances on ships, trains, or pipelines where the gas is converted to CNG before being distributed to end users.
Natural gas is experimentally stored at lower pressures in a form known as ANG (adsorbed natural gas) cylinders, where it is stored at 35 bar (500 psi, gas pressure in natural gas pipelines) in various sponges materials such as carbon and MOF. (organic metal skeleton). The fuel is stored at the same or higher energy density than CNG. This means the vehicle can be refueled from the natural gas grid without additional gas compression, the fuel cylinder can be attenuated and made from lighter and weaker materials.
It is possible to combine ANG and CNG technologies to achieve increased natural gas storage capacity. In this process, known as high-pressure ANG, the high-pressure. CNG tank is filled with an adsorbent such as activated carbon (high surface area absorbent) and stores natural gas through the CNG and ANG mechanisms.
