Characteristics of CNG
CNG has a much higher octane number and lower cetane number, which makes CNG a good alternative for spark ignition engines but unsuitable fuel for compression ignition engines. The higher octane number makes it a superior fuel than petrol; as the octane number of CNG is high, there is no anti-lock additives are required.
It's important to note that gasoline contains various additives and may have different specifications and regulations depending on the country or region. Some of the characteristics are-
* Volatility: Gasoline is highly volatile, meaning it evaporates quickly at normal temperatures. This property allows it to vaporize easily for efficient combustion in engines.
* Combustibility: Gasoline is highly flammable, making it suitable for use as a fuel. It can ignite easily and burn rapidly when exposed to an ignition source, such as a spark.
* Density: Gasoline is less dense than water, which means it floats on the surface of the water. This characteristic is important for fuel storage and transportation purposes.
* Color and Odor: Gasoline is typically colorless or slightly yellowish and has a distinct odor. The odor is mainly due to the presence of additives, such as detergents and anti-knock agents, which are added to enhance performance and reduce engine knocking.
* Chemical Composition: Gasoline is a mixture of various hydrocarbons, primarily obtained from crude oil through refining processes. The exact composition may vary, but it generally consists of hydrocarbon molecules with 8 to 12 carbon atoms, including compounds such as octane, heptane, and isooctane.
* Energy Content: Gasoline is an energy-dense fuel, meaning it contains a significant amount of energy per unit volume. The energy content of gasoline is measured in terms of its octane rating, which indicates its resistance to knocking. Higher-octane gasoline typically provides better performance in high-compression engines.
* Lubrication: Gasoline has limited lubricating properties compared to other fuels, such as diesel. To compensate for this, lubricating additives are often included in gasoline formulations to protect engine components.
* Volatility Control: Gasoline formulations are carefully engineered to control the volatility characteristics of the fuel. This is crucial to ensure the proper operation of the engine across a range of temperatures and conditions.
Physical Properties of CNG
Due to the absence of any lead or benzene content in CNG, the lead fouling of spark plugs and lead or benzene pollution is eliminated. Being a gaseous fuel, CNG mixes with the air easily and evenly.
The physical properties of CNG, unleaded gasoline, and diesel are as below:
| Properties | Unit | Petrol | Diesel | CNG |
|---|---|---|---|---|
| Liquid Specific Gravity | - | 0.74 | 0.8 | - |
| Heat of Evaporation | BTU/LB | 160 | 200 | _ |
| Density Relative to Air | Air=1 | 3.4 | 3.9 | 0.6 |
| Auto Ignition Temparature | Degree Celcius | 232-282 | 225 | 540 |
| Flammability Limit | % in air | 1-8 | 0.6-5.5 | 5-15 |
| Flame Temperature | Degree Celcius | 1977 | 2054 | 1790 |
| Octane No. | _ | 87 | _ | 127 |
| Cetane No. | _ | 10 | 45 | 10 |
Comparison on an energy basis is that 1 kg of Ng is equivalent to about 1.349 liters of petrol or 1.18 liter of diesel. Or on a volume basis, 1 m^3 of NG is equivalent to about 1.10 L of petrol or 1.0 L of diesel. When making comparisons, you may also need to take into account the relative energy efficiency of the engines that use the various fuels.
Conclusion
Generally, engines that are designed for natural gas fuel are slightly more efficient than a similar petrol engine, because they can run at a higher compression ratio. The CNG and diesel engines are similar in size and will have much the same thermal efficiency.
Faq's
1. What are Dual-Fuel Vehicles?
A vehicle that runs either on diesel fuel only, or diesel fuel and natural gas simultaneously. In a dual-fuel vehicle, the combustion of diesel fuel serves to ignite the natural gas.
2. What is a Dedicated CNG Vehicle?
A dedicated CNG vehicle runs on natural gas only. Dedicated CNG vehicles can be petrol-fueled vehicles that have been converted to run on natural gas.
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