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CNG demystified

Rahul Sharma, 01-Jul-2011
14860 Views;

Part 1

CNG demystified

We explain the various components and their functions in a typical CNG kit

Use of CNG in cars can be seen in most cities now. The obvious reason for it is the exponential increase in the price of petrol. The use of CNG as a fuel also reduces emissions significantly. Carbon Monoxide (CO) emissions are reduced by over 70 per cent and hydrocarbon emissions by over 40 per cent as compared to cars using conventional fuel. Carbon Dioxide emissions, a cause for global warming, are also reduced significantly, by 10 per cent. The running cost of CNG is at least two times as less as that in a petrol car. CNG is also one of the combustible gases which can aid in running of engine and is claimed to prolong the life of the engine as well. Increase in CNG usage also corresponds with increased availability and reduced wait times at pumps.

If you have got a CNG kit fitted then you need to be aware of the basic operation and all the different components and their functions so that you are able to better understand and so can derive a better engine life, performance and also increase your safety while driving the vehicle. Greater understanding will also help you assess problems that might crop up in future.

1. Reducer

Reducer

CNG is stored at a very high pressure (200BAR). The job of the reducer is to reduce the pressure to 0.5BAR before it enters the intake manifold using a three stage process. As it has a critical function get it checked if the car’s performance shows even a slight dip.

2. Emulator

Emulator

It is the ECU of the fuelling system and is found on all fuel injected cars fitted with a CNG system. It controls the amount of natural gas that is to be supp lied to the engine depending on the load requirements. It requires no manual adjustments and can automatically adapt to the different working conditions and use of the vehicle.

3. Changover Switch

Changover Switch

The changeover switch is located in the cabin and is used to switch between petrol and gas. The car starts on petrol and reverts to CNG automatically and can be switched to petrol while driving. Though remember that continuously switching between fuels puts extra load on the system.

Part 2

4. Hi-pressure Piping

A high pressure pipe travels from the cylinder in the boot to the engine bringing the gas. It travels from underneath the car; hence it’s advisable to get the underbody checked. A scraped undercarriage could damage the piping even though it is covered in PVC.

5. Shut-off valve

The valve is used to shut down fuel supply to the engine. If you are not going to use the car for a long time, start the engine and let it run on CNG for a while. Then close the valve and let the engine die down. This will ensure that there is no gas in the pipelines and the car can be safely parked.

6. CNG Cylinder

A CNG cylinder is usually placed in the boot on a raised frame. They are built to withstand of pressures of 300BAR though working pressure is only 200BAR. It is not advisable to keep luggage on top of it, especially in summer. A 100-litre capacity cylinder can hold upto 24.88 cubic metres of gas.

7. Timing advancer

A car running on gas runs at almost 15 per cent less power output while running on CNG . As CNG have a slower combustion time in comparison to petrol, therefore it is necessary for the spark to ignite in advance in comparison to the original point. The timing Advance Processor modifi es the original ignition point, calculated for a correct fuel running of the car.

8. Refuelling valve

The refuelling valve has bushes in it to hold the nozzle while filling the gas. With use over time there is a chance of the bushes wearing out, which can give problems during refuelling the car. A replacement costs around Rs 1,000 depending on the manufacturer. It is the one which has a pressure gauge located next to it, which shows the amount of gas present in the tank.

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