CNG is an acronym for Compressed Natural Gas, which is ordinary Sui Gas (natural gas) that is widely used in homes, industries and factories. In this section, the information is presented under following headings:

• - Economic advantages of using CNG
• - Description of CNG Conversion Kits
• - Description of CNG Cylinders
• - What is a good conversion system
• - Effects on engine performance
• - Safety
• - Future Outlook (Diesel to CNG)

Conversion of vehicles to CNG:

Conversion of vehicles to CNG involves installing a Conversion Kit and a cylinder in the vehicle.

Basic Components of a CNG Conversion Kit:

Pressure Regulator: This is the heart of the system. It provides the system with fuel at a consistent operating pressure even if the fuel storage pressure varies.

Mixer: Mechanical device which uses the Venturi principle to ensure correct air/fuel mixing in both stationary and dynamic conditions.

Fixed venturi mixer: A conventional, old style venturi mixer, which unfortunately not only affects the drive but also does not completely fulfil the prime objective of conversion i.e. reduced fuel and maintenance costs.

Variable venturi mixer: This is an advanced and technically sophisticated type of mixer which dramatically improves the drive of the vehicle, reduces vehicle maintenance, and reduces fuel costs due to improved mixing.

High Pressure Solenoid : It allows gas to flow through only when the engine is running and the switch is in the "gas" position.

Petrol Solenoid valve: It cuts off the flow of petrol to the engine during gas operation.

Filling Valve: This device is installed in the engine compartment between the storage cylinder and the regulator, includesa a connection to the refueling system and a manual ball device to open/shutoff gas in case of an emergency or for maintenance.

Pressure Indicator: Displays the level of natural gas remaining in the storage cylinder.

Change over Switch: An electronic control module whose function is to allow the user to select the desired fuel (Gas/Petrol) at any time.

High Pressure Piping: The gas from the cylinder goes to the engine compartment through a pressure pipe which is also connected with the refueling system.

Kits are of two types

Electronic Kit: Controlled by the high impulse of the ignition coil. In this type of kit the gas level indicator has four displaying lights and as the gas pressure goes down the light starts switching off indicting the gas pressure at every level.

Vacuum Kit : This kit is operated by the engine vacuum. In this type the gas level indicator has only one light and a reserve indication.

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Effects of using CNG on the Engine:

The life of an engine actually increases by using CNG.

This is due to the fact that :

• CNG enters the engine in the form of gas whereas petrol enters in the form of a spray or mist. The spray/mist washes down the lubricating oil from the top piston ring area thereby increases the rate of depreciation of the engine.
• The Octane Number of CNG is 130 as compared to 87 of gasoline. Therefore, when gas and air in the correct proportion are brought together, they mix thoroughly and rapidly which improves the combustion efficiency.

What is a good conversion system:

A good conversion system should operate as close to gasoline as possible, save fueling costs, reduce the vehicle emission, be safe and reliable and durable to last the life of the vehicle. This can only be achieved / accomplished with a level of conversion technology that includes a variable venturi carburetor.

Unfortunately, in Pakistan the technology being employed for conversion of vehicles is quite outdated, resulting in poor vehicle performance, fuel economy and power loss. Kits which are being installed currently are of a fixed venturi type which results in uncontrolled mixing of air and fuel (gas). Whereas the kits being installed in other parts of the world are of mixer or variable venturi carburetor type which dramatically improves the drivability, reduce vehicle maintenance (by eliminating constant engine adjustment), reduces fuel costs due to improved fueling (better mileage) and more controlled vehicle emission.

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While planning to convert his/her car to CNG a consumer is concerned about

Safety: Generally the first question people ask to a converter is : Is it Safe ?
Factual data has proven that CNG is safer than gasoline (petrol).

Compressed Natural Gas	Gasoline (Petrol)
It has a self-ignition temperature of 700C.	The self-ignition temperature of gasoline is 415C.
It has a specific gravity of 0.587, means it is lighter than air. So if it leaks it rises up and dissipates into the atmosphere.	Petrol in case of a leakage puddles onto the ground causing a danger of catching fire.
CNG storage cylinders are made of special materials to withstand high pressure. They are made entirely of a single piece so there are no joints. They are fire and bulletproof.	Petrol tanks are made of ordinary steel sheets.

Economy::

CNG is the most economical fuel and saves more than 55% of your fuel expenditure over petrol. The lubricating oil life is considerably extended too because CNG does not contaminate and dilute the crank case oil. It eliminates frequent vehicle maintenance. Due to the absence of any lead content in CNG, the lead fouling of plugs is eliminated and plug life is greatly extended.

	Petrol.	CNG.	Savings.
Cost per liter.	Rs- 58.71	Rs-30.25	Rs-28.46
Cost of 8 Litres.	Rs-469.68	Rs-242.80	Rs-226.88
Monthly Concumption.	Rs-14090.4	Rs-7260.00	Rs-6830.4
Yearly Consumption.	Rs-169084.8	Rs-87120.00	Rs-81964.08

Drivability:

CNG provides easy starting, reliable idling and smooth acceleration. While running on CNG, there is a power loss of approximately 5-15%, which can be minimized by using kits with a variable mixer and proper tuning (advancing the spark timing).

Future Outlook:

In the future the main focus of the CNG industry is to convert diesel driven vehicles to CNG. This technology has been developed in many parts of the world and has mainly been used to convert heavy transport vehicles, like buses, trucks, etc. As compared to gasoline conversion, the conversion of diesel is much more expensive yet much more efficient. Moreover, it is a customized kit that is designed for specific engines.

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