PakCNG.com- CNG FAQ, CNG cars frequently asked questions. CNG Cars and automobiles.

What is CNG and why should I go in for it?
CNG stands for Compressed Natural Gas. It is one of the most viable alternatives to traditional fuel energy resources for the automotive industry. CNG is low in pollutants, high in calorific value and heat yield, economical and available in abundance globally.

Reasons for switching over to this alternate fuel are mainly
1. Economic benefit: The cost of CNG is almost a third of the cost of Petrol in terms of calorific value resulting in substantial saving in fuel cost, and investment on the CNG kit is paid back in a short period

2. Environment friendly: The use of CNG as a fuel reduces vehicular exhaust emissions significantly. Carbon Monoxide emissions are reduced by 70 to 90% and Hydrocarbon emissions by 40 to 60% as compared to vehicles that use the conventional fuel - Petrol. Carbon Dioxide emissions, a cause for global warming, are also reduced significantly by 10%

3. 100% Income Tax Depreciation: Corporate Organizations, firms, etc. can claim 100% depreciation on a CNG Conversion Kit as this is a pollution controlling equipment. Organizations that buy CNG Conversion Kits should consult their Income Tax Consultants and avail of the depreciation benefits

4. Flexibility and ease of use: The basic engine characteristics of a vehicle are retained while converting it to run on CNG. The vehicle therefore is capable of running either on Petrol or CNG at the flick of a switch on its dashboard.

The Fuelling Process
Pakistan has one of the largest number of refueling stations available now. And this figure is fast increasing.

CNG is stored at compression stations which are directly connected with the gas pipeline. Here the gas is compressed to a required pressure and aids fuelling. CNG can also be transported to other retail outlets by cylinder trucks. these trucks carry a number of cylinders which provide CNG to fuel stations which are not connected by pipelines. These fuelling stations could be placed alongside petrol and diesel pumps too. the whole process requires proper infrastructure and transportation.

What does the kit comprise of?

1. The Cylinder
The cylinder is used to store CNG at a working pressure of 200 bar. It is fitted with a shut-off valve and a safety burst disc. The cylinders are type approved by the Chief Controller of Explosives, Government of India

2. The Vapor Bag
Fitted onto the cylinder, the Vapor Bag is used to enclose the cylinder valve and the pipes connecting it and is vented out of the car

3. The High Pressure Pipe
This High Pressure Pipe connects the refueling valve to the CNG Cylinder and Pressure Regulator

4. The Refueling Valve
The Refueling Valve is used to refuel the CNG cylinder

5. The Pressure Regulator
The Pressure Regulator has a Solenoid Valve to shut-off gas supply to the engine. The CNG stored at a high pressure in the cylinder is reduced to just below atmospheric pressure by this unit. This negative pressure is also a safety feature that will not allow gas to pass through when the engine is not running

6. The Gas-Air Mixer
The Gas-Air Mixer is a unique component, specially designed to suit each engine model. It precisely meters gas fed into the engine

7. The Petrol-Solenoid Valve
The Petrol-Solenoid Valve is used to cut off petrol supply to the engine when it is run on CNG

8. The Selector Switch
The Selector Switch is fitted at the dashboard, enabling the driver to choose either the CNG mode or the petrol mode of operation. The electronics built into this unit also ensures safety by switching off the gas solenoid whenever the engine is switched off. It also serves as a fuel indicator for the quantity of CNG available in the cylinder

Do's and Don'ts for CNG conversion
Ensure that the workshop is authorized and observes Safety Standards and Code of Practices in kit installation and commissioning.

The kit, including the cylinder must be of the type approved for the make of the car. Do not buy components from different sources and install the kit yourself.

Ensure that the car undergoes the required pre-conversion checks thoroughly. After the connections are made, ensure a complete and thorough leak test of the gas system.

Installer's certificate must be collected from the workshop.

Any modification or improvisation should only be done at an authorized workshop.

Acquaint yourself with the mechanism of CNG and the precautions essential for a CNG vehicle. Follow them strictly.

In case of an accident, get the vehicle thoroughly checked by an authorized workshop and obtain re-certification.

Do not install an LPG, Propane or any other cylinder in place of a CNG cylinder. It is illegal and unsafe.

Additional premium is charged by the insurance company for CNG run cars. One should run the vehicle only after the risks of the additional CNG kit system are covered by the insurance company.

How does CNG affect the environment?
If you would like to play a part in reducing the alarming pollution levels in your city then switch to CNG right away. CNG reduces the emission of harmful pollutants. It reduces Carbon Monoxide emission by 80% and Hydrocarbon emission by 45%.

What’s different about CNG against other gases which are in use currently?
In the past, gas-fuelled automobiles used LPG (Burshane). Today it is compressed natural gas (CNG) that is in use. Methane is the prime component of CNG while LPG is a blend of propane, butane and some other chemicals.

Can an existing LPG vehicle run on CNG?
An LPG-fuelled vehicle will not run on CNG as the two fuels are different from each other, have differing calorific values and need different air-fuel ratios for combustion. CNG has to be stored at relatively higher pressure in a cylinder than LPG, so the same cylinder cannot be used for both gases. A vehicle will need specific conversion for CNG operation.

Does CNG have odors like LPG?
No, a vehicle running on CNG is as odor-free as a car running on petrol. If any odor is found which is similar to domestic natural gas in a CNG vehicle, then the incident should be reported immediately to CNG Station for a leak check.

Will my car still run on petrol if I run out of CNG?
The petrol carburetor is retained during conversion for CNG so that the vehicle will still run on petrol. A switch on the dashboard allows one to make instant changes of fuel sources.

How much will I save on CNG?
Savings on fuel cost by using CNG will depend on size and fuel consumption characteristics of the vehicle, as well as mileage. As we have seen in the CNG Omni the cost per kilometer incurred was nearly half that of the costs incurred by the petrol van.

Should I use petrol occasionally?
Occasional use of petrol serves to lubricate the carburetor besides making for better running of the engine.

Is the CNG option safe?
Four key features make CNG a safer fuel than petrol, diesel or LPG. With specific gravity of 0.587, it is lighter than air so in case of leaks, it rises up and dissipates into air. (Other fuels form puddles on the ground in case of leaks.) CNG has a 700 degree Centigrade ignition temperature compared to 455 degree Centigrade for petrol. The range of 4 to 14 per cent in which CNG mixes with air by volume for combustion is small. Storage is far safer than for petrol, as CNG cylinders are designed and built from special materials and to high safety specifications.

What is the pressure of CNG in a cylinder?
CNG is filled to a maximum of 200kg/cm (about 3000psi/g) in a cylinder.

Is refueling cylinders a safe option with such high pressures involved? Is it safe even in an accident?
Refueling is safe as the cylinder is made from a single piece of special steel alloy, with no welded joints, and each cylinder is tested as per international specifications before being installed. A ‘burst’ disc ensures safety as in case of inadvertent high pressure filling, or fore, the disc ruptures so no excess pressure situation over the specified level is created. Italy, New Zealand, Argentina and the US are countries where CNG has been in use for years, and it has been categorized as being safer fuel than petrol.

Will CNG harm my engine in any way?
Use of CNG serves to extend life of lubricating oil as CNG will not contaminate or dilute crankcase oil. Fouling of plugs is eliminated and plug life is enhanced as CNG does not contain any lead. CNG enters the engine as gas while petrol comes in as spray or mist which washes down the lubricating oil from the piston ring area to raise the rate of engine depreciation. This reduces maintenance costs and engine life goes up.

Why are exhaust gases literally non-existent in CNG vehicles?
A major positive aspect of CNG use is that being a natural gas (methane content) its exhaust emissions contain just water vapour and minuscule quantity of carbon monoxide, no carbon or other particles. Being virtually pollution free CNG driven vehicles meet the most stringent of emission standards worldwide.

How does a CNG vehicle compare to a petrol powered one on performance parameters?
Easy starts, steady idling and smooth acceleration are virtues of CNG run vehicles. Power loss of 5-15 per cent means that acceleration is slower, which can be eradicated with spot-on tuning of the CNG kit, by advancing spark timing to derive benefit of its high octane rating. However the power loss is less than noticeable in city driving.

Does CNG equipment require special service?
The CNG kit is easy to service and durable to boot. For optimum efficiency regular checks, every 10,000km, are prescribed.

Can diesel vehicles be converted to CNG?
Yes, diesel vehicles can be converted to CNG and most public transport in metros which previously ran on diesel now use CNG.

Has the CNG movement fared well in developed or developing countries?
Having been around since the 1920s, Italy has 240 stations and 300,000 cars running on CNG, New Zealand has 250 CNG pumps and 250,000 vehicles. Argentina has undertaken a major CNG programme and has 700,000 CNG run vehicles. Thailand, Indonesia, Bangladesh, Canada, France, Pakistan, India, Holland, Australia, UK and the US have also taken to CNG in smaller measure. Availability of natural gas and socio-economic conditions are the two factors conducive to bring about switch to CNG fuel.

How does a country benefit if CNG were to be used on a large scale?
A country can have cleaner environment with comprehensive use of CNG, while new job opportunities and economy are other benefits of using CNG. Motorists will have to pay lesser for fuel and certain countries like India which has huge reserves of CNG can also export it to generate revenue. This will also reduce the expense of fuels we have to import.

How do NGV's work?
The only major difference between a gasoline vehicle and an NGV is the fuel system. Natural gas is compressed to between 3,000 and 3,600 pounds per square inch (200 bar) and is stored on board the vehicle in cylinders installed in the rear, undercarriage, or on the roof. When natural gas is required by the engine, it leaves the cylinders, passes through a master manual shut-off valve and travels through a high-pressure fuel regulator located in the engine compartment. The natural gas is injected at atmospheric pressure through a specially designed natural gas mixer where it is properly mixed with air. Natural gas then flows into the engine's combustion chamber and is ignited to create the power required to drive the vehicle. Special solenoid-operated valves prevent the gas from entering the engine when it is shut off.

What about the vehicle's power?
Gasoline vehicles converted to natural gas are subject to a small power loss when running on natural gas; however, vehicles designed specifically to run on natural gas will have no loss of power and may even have greater power and efficiency. Natural gas has a 130 octane rating, compared with 87 to 96 octane rating of gasoline.

How much energy does Compressed Natural gas release compared to petrol?
A direct answer to your question is that the energy content of natural gas (NG) is about 47 MJ/kg or 40 MJ/m3. (gross heating value). The values for a typical petrol are 60 MJ/kg and 44 MJ/liter. Another comparison on an energy basis is that 1 kg of NG is equivalent to about 1.33 liter of petrol or 1.22 liter of diesel. Or on a volume basis 1 m3 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. 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 NG and diesel engines of similar size will have a much the same thermal efficiency.

What is the miles per gallon equivalent of natural gas compared to gasoline?
If the NGV is an original Equipment Manufacturer (OEM) model, it will have been designed to make the most of the excellent properties of Natural Gas - eg it will have a higher compression ratio than the petrol model and different ignition timing - and you could expect to see an improvement in performance and fuel consumption on an energy basis. This might be about 5% or more. Of course you might then drive faster, and not have any advantage. If the car has been converted from gasoline to NG and you can choose to run on either fuel (i.e. a bi-fuel vehicle) then it is not possible to make the most of the higher octane rating of the NG. In this case the change in fuel consumption will depend very much on the vehicle and engine design and on the conversion equipment used and how it is tuned. In this case you might expect an increase of possibly 5% in consumption. However the tune may be optimized to a particular power and speed range and if you can hit this you might get a small improvement. There may be more scope to achieve this on a high capacity engine with reserves of power. On a smaller engine there may be a noticeable drop in power and your consumption could increase if you try to match the old on-road performance.

Cylinders in Accidents
A pressurized gas cylinder is probably the strongest component on the vehicle. Vehicles that totally destroyed in collisions show the only discernible component being the intact gas cylinder. It is unlikely that cylinders will rupture due to collision impact.

Regarding the danger of fire from leaking cylinders, all we have is the experience to date that indicates that such an event is unlikely to occur. In North America there was a problem with leaking type 4 designs from a particular manufacturer, but there has never been an ensuing fire. The risk of fire from leaking cylinders must be low since there are well over a million CNG vehicle installations worldwide that have not experienced such problems.

It is worth pointing out that natural gas is lighter than air and in the unlikely event of a leak from piping or container the gas will dissipate upwards quite quickly. In the case of petrol and LPG the vapor given off is heavier than air and will tend to pool near the ground. This is where there is a strong risk of some ignition source. In general terms diesel ranks high in terms of safety, but most people rank Naturak Gas next.

What are the factors which affect the fuel efficiency of CNG?
In the first place let us list the energy content of the fuels you mention. Using units of MJ per kilogram, the net heating values of petrol, diesel, LPG and NG are about 45, 43, 46, and 44; the net heating value does not include the heat in the water vapor of the combustion products. If you look up the gross heating values - which do include this, the values are different (higher). So the differences between the fuels are not large. But the values will also vary quite a lot depending on the composition of the fuel - particularly for NG and LPG.

We now need to consider the way in which different engines use the fuels - in particular the efficiency. The engine thermal efficiency is a function of many different factors but perhaps the most important one is the engine compression ratio. The higher the compression ratio the higher is the theoretical and also the actual efficiency. The maximum compression ratio (CR) different fuels can tolerate in fact defines the efficiency. Since diesel used in a compression ignition engine can operate at say 14:1 the diesel will be expected to have the highest efficiency - lets say 40% as an upper limit. The next highest efficiency in the fuels comes from CNG, which can operate at say 12:1. with an efficiency of say 35%. It is possible to run an engine on CNG at 14:1 but that is the very upper limit. We would not expect to be able to run petrol and LPG engines at much more than 9:1 and an efficiency of about 30%. These efficiencies are the upper limits and at full load - in normal operation they will be lower than the values quoted, but in much the same proportion. The main reason for the differences is the variation in limiting CR for the different fuels. So here is a starting point for a discussion of the differences in efficiency.

As far as fuel energy comparisons go (and this does not take into account the different engine efficiencies), 1 kg of NG is equivalent to about 1.33 liters of petrol or 1.22 liters of diesel - but of course occupies a greater volume. Or 1 cubic meter of NG at atmospheric pressure is equivalent to 1.10 liters of petrol and 1.00 liters of diesel.

Note that there are a lot of other factors that we have not considered - for example the diesel engine will be much heavier than the other engines, and the gaseous fuels will need pressure vessels to contain them. Having established how much energy you get from the different fuels and how efficiently the different engines can use the fuels, you will be able find out how much they cost and then work out a cost per km or mile. In many countries CNG will come out as best value and that diesel will be next, followed by LPG and then petrol. But prices do vary a great deal. Incidentally if you have a petrol engine that has been converted to use NG you will not achieve the high efficiency quoted above because the compression ratio will be fixed at the level required for petrol - you will only get the benefit of higher efficiency in an OEM.

What are the economics of small vehicle conversion?
In very general terms the smaller the vehicle the longer is the payback period for the cost of conversion. This is because the fuel consumption - and therefore savings - for the smaller vehicles is lower, and at the same time the cost of conversion does not go down much with vehicle size. The cost of the fuel control system stays much the same and the price of a smaller storage cylinder will not be much lower (and in a small vehicle it is more difficult to find a space for the cylinder).

It may be difficult to justify the conversion on an economic basis, but this does depend on annual mileage. Do a rough sum on the basis of saving half (or whatever the price differential is in your area) of your fuel costs in a year. You should expect better than a three year payback on the basis of economics.

Environmental benefits and lower maintenance costs will be small.

Check where you would be able to find space for the storage cylinder which must be sized to meet commuter needs. And of course allow something for the satisfaction of knowing that you are lowering your output of hydrocarbon emissions.

Is driving around with cylinders full of gas under pressure dangerous?
Thick-walled reinforced aluminum cylinders, steel cylinders or 100% composite materials are used to store compressed natural gas as a vehicle fuel. These cylinders are manufactured and tested in compliance with strict regulations, and have withstood severe abuse testing under conditions far more stringent than tanks designed for storing gasoline. Natural gas vehicles submitted to test crashes up to 52 miles per hour, which have been totally destroyed, but show little or no damage to the compressed gas cylinders. Bonfire and dynamite tests push cylinders to temperature and pressures exceeding specified limits showing that compressed natural gas cylinders are durable and safe. Of course, as with all fuel systems, these cylinders are not indestructible and should be inspected periodically to ensure that no surface damage has occurred.

What are the conversion factors for natural gas?
Methane values are fixed and can be found in any chemical handbook, while the composition of natural gas varies with source and time so try to find a local value. Approximately, 1kg NG is equivalent to about 1.33 liters (L) of petrol or 1.22 L diesel. And 1 cu meter of NG is equivalent to about 1.10 L of petrol or 1.00 L diesel.

Do we have enough natural gas in Pakistan to use in the transport sector on a large scale?
Yes, we have enough resources, if we convert 100,000 vehicles to CNG, the quantity of gas would be 15 million cubic feet per day, which is only 0.7% of our total gas consumption while it will reduce 15% gasoline consumption of country. This would in no way drastically alter the production pattern of our gas fields neither would it significantly reduce the life of our proven gas reserves. And with the intensified exploration and development program being followed these days, we bound to discover more gas to add to our reserves. The gas used for CNG would be much less than the new reserves thus added.

What is the CNG Dual Fuel System?
Under the CNG Dual Fuel System a compressed natural gas Conversion Kit is added to a vehicle with no major modifications to the vehicle's system. In fact the capability of the vehicle is enhanced to include operating on an alternative fuel ie: CNG