Compressed natural gas (CNG) is a fossil fuel substitute for gasoline, diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels. It is also much safer than other fuels in the event of a spill as natural gas is lighter than air, and disperses quickly when released. CNG may also be mixed with biogas, produced from landfills or waste water, which doesn’t increase the concentration of carbon in the atmosphere.
CNG is made by compressing natural gas, which is mainly composed of methane [CH4], to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 200–248 bar (2900–3600 psi), usually in cylindrical or spherical shapes.
CNG is used in traditional gasoline internal combustion engine cars that have been converted into bi-fuel vehicles (gasoline/CNG). Natural gas vehicles are increasingly used in the Asia-Pacific region (especially Pakistan and the Indian capital of Delhi ), Latin America, Europe, and North America due to rising gasoline prices. In response to high fuel prices and environmental concerns, CNG is starting to be used also in tuk-tuks and pickup trucks, transit and school buses, and trains.
The cost of this conversion is a barrier for CNG use as fuel and explains why public transportation vehicles are early adopters, as they can amortize more quickly the money invested in the new and cheaper fuel. In spite of these circumstances the number of vehicles in the world that use CNG has grown steadily at a 30 percent annual rate.
CNG’s volumetric energy density is estimated to be 42% of liquefied natural gas’s because it is not liquefied, and 25% of diesel’s.
1. Due to the absence of any lead or benzene content in CNG, the lead fouling of spark plugs is eliminated.
2. CNG-powered vehicles have lower maintenance costs when compared with other fossil fuel-powered vehicles.
3. CNG fuel systems are sealed, which prevents any spill or evaporation losses.
4. Increased life of lubricating oils, as CNG does not contaminate and dilute the crankcase oil.
5. CNG mixes easily and evenly in air being a gaseous fuel.
6. CNG is less likely to auto-ignite on hot surfaces, since it has a high auto-ignition temperature (540 °C) and a narrow range (5%-15%) of flammability.
7. Less pollution and more efficiency: CNG emits significantly less pollutants such as carbon dioxide (CO2), unburned hydrocarbons (UHC), carbon monoxide (CO), nitrogen oxides (NOx), sulfur oxides (SOx) and particulate matter (PM), compared to petrol. For example, an engine running on petrol for 100 km emits 22,000 grams of CO2, while covering the same distance on CNG emits only 16,275 grams of CO2. CNG is essentially methane, i.e. CH4 with a calorific value of 900 kJ/mol. This burns with oxygen to produce 1 mol of CO2 and 2 mol of H2O. By comparison, petrol can be regarded as essentially benzene or similar, C6H6 with a calorific value of about 3,300 kJ/mol and this burns to produce 6 mol of CO2 and 3 mol of H2O. From this it can be seen that per mol of CO2 produced, CNG releases over 1.6 times as much energy as that released from petrol (or for the same amount of energy, CNG produces nearly 40% less CO2).] The corresponding figures are 78 and 25.8 grams respectively, for nitrogen oxides. Carbon monoxide emissions are reduced even further. Due to lower carbon dioxide and nitrogen oxides emissions, switching to CNG can help mitigate greenhouse gas emissions. The ability of CNG to reduce greenhouse gas emissions over the entire fuel lifecycle will depend on the source of the natural gas and the fuel it is replacing. The lifecycle greenhouse gas emissions for CNG compressed from California’s pipeline natural gas is given a value of 67.70 grams of CO2-equivalent per megajoule (gCO2e/MJ) by the California Air Resources Board (CARB), approximately 28% lower than the average gasoline fuel in that market (95.86 gCO2e/MJ). CNG produced from landfill biogas was found by CARB to have the lowest greenhouse gas emissions of any fuel analyzed, with a value of 11.26 gCO2e/MJ (over 88% lower than conventional gasoline) in the low-carbon fuel standard that went into effect on January 12, 2010.
▪ Lowest Cost Fuel – As low as $.70-80 a GGE (Gasoline Gallon Equivalent) If your car gets 30 mpg on gasoline you will still get the same 30 mpg on CNG and at a lower cost. In many areas the cost of natural gas is regulated, keeping the price low.
▪ Domestic Fuel – Not dependent on foreign oil and their constant price increases. You will save even more in the future as gasoline continues to rise faster than natural gas.
▪ Environmentally Friendly – Fewer emissions as hydrocarbons are virtually eliminated.
▪ Engine Runs Cleaner and Lasts Longer – No Carbon Deposits Which Create Friction and Engine Wear.
▪ Ignition (Spark) Plugs Stay Cleaner and Last Longer – No carbon deposits to clog and dirty the plugs.
▪ Catalytic Converter Lasts Longer – No carbon deposits to dirty and clog the catalytic converter.
▪ Fewer Oil Changes – Carbon deposits which dirty the engines oil are eliminated.
▪ Engine Runs Quieter – Less engine noise due to the higher octane of natural gas.
▪ Bi-Fuel – Change to either fuel with the push of a button.