Advantages
- Due to the absence of any lead or benzene content in CNG, the lead fouling of spark plugs is eliminated.
- CNG-powered vehicles have lower maintenance costs when compared with other hydrocarbon fuel-powered vehicles.
- CNG fuel systems are sealed, which prevents any spill or evaporation losses.
- Increased life of lubricating oils, as CNG does not contaminate and dilute the crankcase oil.
- Being a gaseous fuel, CNG mixes easily and evenly in air.
- CNG is less likely to ignite on hot surfaces, since it has a high auto-ignition temperature (540 °C) and a narrow range (5%-15%) of flammability.
- 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 mole of CO2 and 2 moles 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 moles of CO2 and 3 moles of H2O. From this it can be seen that per mole 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.
Read more about this topic: Compressed Natural Gas
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