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Written by CH Cheah
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Tuesday, 10 June 2008 09:09 |
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 With the rising costs of petrol (gasoline) many vehicle owners are looking into alternatives with which they can replace petrol with. Compressed Natural Gas (CNG) appears to be a viable alternative which promises to save cost, less polluting to the environment and can be easily retrofitted into existing vehicles. However most may still have concerns on safety, efficiency, miles per gallon and performance (power loss) of the vehicle once converted to CNG. What is the real deal in vehicles burning CNG (NGV). I hope to answer some of these questions in this article.
Environment Friendly
Natural gas requires little processing before use (unlike gasoline which requires the refinery process). Chemically, natural gas contains 90% methane with smaller amounts of ethane, propane, butane, carbon dioxide and other trace gases. The high methane gives natural gas a high octane rating (120 - 130).  Though methane itself is a greenhouse gas, it has clean burning characteristics, allowing high efficiency and low emissions. According to ConsumerReports.org, natural gas burns cleaner than gasoline. Compared to gasoline burning it reduces carbon monoxide by 90 - 97%, nitrogen oxide by 35 to 60% and non-methane hydrocarbon emissions by 50 - 75%. Though not a renewable resource, natural gas is plentiful in supply. According to Natural Gas Supply Association (USA), current reserves point to another 60 years of supply.
CNG cars are typically greener than hybrids like Toyota Prius or the Civic hybrid.
Safety
Safety of CNG vehicles is on par or higher than with gasoline. The pressurized tank is built to withstand severe impact, temperature and environment exposure. CNG lighter than air, it will evaporate quickly into the atmosphere when there is a leak instead of collecting as a puddle under the car like gasoline would. According to the Clean Vehicle Education Foundation (USA) natural gas has very limited flammability. It will not burn at concentrations below 5% or above about 15% when mixed with air. Gasoline and diesel burns at much lower concentrations and ignite at lower temperatures. Natural gas is naturally odorless, however an odorant is added to provide a distinctive unpleasant smell which is easy to recognize and detectable by the human nose at one-fifth of the gas's lower flammability limit. Natural gas is non toxic when evaporated into air. CNG storage tanks also have an automatic relieve valve. When the pressure or temperature is excessive this valve will open and release the gas into the atmosphere to reduce the pressure.
 Performance
Performance is comparable to petrol powered vehicle. However some people have reported up to 15% power loss when compared to gasoline. This is because unlike the gasoline system which delivers full power until empty, CNG vehicles typically achieved similar power to gasoline when the CNG tank is under the full pressure of 3000psi, but when pressure drops to 300-400psi you may have difficulty going up hills. When power is required there is always the option of switching back to gasoline at the flick of a switch, so this may not be a real problem. A study on New York City taxis shows maintenance cost is also reduced for CNG vehicles over those running on regular gasoline. The fact that CNG burns cleaner may be a contributing factor to this observation.
Though the CNG tank is larger than regular gasoline tank, you get fewer miles per liter because the CNG tank is considered empty when pressure drops below a low limit. Hence it actually carries less usable fuel per volume of tank. You may experience a mileage loss per full tank of 35% as compared to regular gasoline. Another disadvantage is also you will typically have half the trunk space because of the space taken by the CNG cylinder.
Cost Savings
What kind of cost savings can you expect from you conversion to CNG? The conversion itself may set you back around RM2000-3000 (USD645 - 970) for a carbureted car and around RM4000-5000 (USD1290-1612) for a fuel-injection car. However with the volume of CNG conversion currently on the rise, economics of scale may push this price down a little. Readers who got a better deal would do us a favor to let us know about it.
Based on Jun 2008 cost of gasoline and CNG in Malaysia and after some conversations with taxi drivers we estimate (mixed city and highway driving) these potential savings:
Gasoline: RM0.35 / km (at retail pump price of RM2.70/per litre)
CNG: RM0.08 / km (at retail pump price of RM0.68/per litre)
Do I see that smile on your face!
The Nitty Gritty Stuff
 Ok, some things that you might want to keep in mind in deciding on a CNG conversion for your vehicle:
- The CNG cylinder that you need to install in your trunk is huge, typically larger than the standard gas cylinder that you use for cooking at home. There are also several sizes of the CNG cylinder available. Just remember smaller tank equals less range for your vehicle when running on CNG. But it also means more trunk space.
- Some people have reported that acceleration of their vehicle using CNG may not be as good as when running on gasoline and you have to floor the pedal more. However for typical city traffic, this will not be a problem.
- You need to plan on when to refuel your CNG as during peak hours there can be a long queue.
- The problem above is due to the dearth of CNG refilling stations in this country at this moment.
On the last point of lack of refilling stations above, our neighbor, Thailand, is fast moving to adopt more CNG powered vehicles. According to Bangkok Post on Jun 6th 2008, four companies in Thailand are starting to make CNG cylinders to meet the soaring demand. In Thailand there are currently about 78,000 CNG vehicles on the road and this is expected to rise to 332,000 by 2012. Authorities are planning to increase CNG pumps from 171 to 740 to meet the demands. I wonder if in Malaysia, the government have similar plan in mind?
CNG is cheaper now, but with demand who knows? The greed factor in the CNG supply chain's owners may affect the increase of CNG's retail price. That would mean that the time to recoup you investment in the CNG conversion would be pushed out further into the future.
There are clear advantages now for CNG powered vehicles and the facts have been laid out. The next move belongs to you.
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Compressed Natural Gas (CNG) Vehicles (NGV) Pros and Cons - Facts on Cost, Safety and Performance
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