Dear Sonil,
CNG installation is beneficial only if your daily running is high on a consistent basis for a considerable period of time.
Quickly:
Pros:
1. Cheaper than petrol. However, price differs from state to state. A quick calculation would let you know how much you shall have to drive after CNG installation in order to break even.
2. Cleaner than petrol: If you are the environment friendly type, then you'd be happy to note than CNG pollutes much lesser than petrol.
3. Cleaner engine: CNG is a clean burning fuel, so your engine shall not have to cough due to carbon deposits in the long run.
4. Kitna deti hai?: CNG pe zyada deti hai (running on CNG shall give more 'average' than running on petrol).
5. Safety first: RTO authorised CNG tanks are built like Dara Singh. Also, when petrol leaks, it evaporates relatively slowly; a spark in this case would translate to Dhoom 3. CNG on the other hand evaporates immediately and hence the risk of an explosion is less.
Cons:
1. Economics: CNG kits don't come free. Initial outlay could range from anything between Rs. 30000-45000. Then its the matter of recovering this initial cost.
2. Marginals get marginalized: The calorific value (energy = heat produced by burning 'x' amount of fuel) of CNG is lesser than that of petrol. Therefore, your engine will lose bhp and torque (in simple terms, power) when you would run it on CNG. How much power is lost differs from engine to engine but it would be safe to assume that it could be from 10% to 20%. You would feel it when you drive.
3. Honey, does my bum look big in this?: CNG cylinder would occupy your boot space and would weigh your car down. In an i10, you would be left with ZERO boot space.
4. Why is everyone looking at me?: Most CNG kits require you to open your bonnet for a refill. Nothing wrong in this, but still...
5. Such a long journey: Though finding CNG stations in Delhi is not a big problem, you would have to think twice before embarking on a long trip as CNG bunks are still rare to find in the country.
6. Time and tide wait for no one: A CNG kit in an i10 would probably take around 8 kgs of CNG in one go which means frequent trips to the CNG station.
7. Warranty: Get an aftermarket CNG kit fitted and your warranty goes for a six. By the way, is your i10 in warranty period? If yes, then please check out sequential CNG kit for the i10 offered by Hyundai.
Apart from all this, there is some talk that CNG harms the engine in the long run but I have seen engines fitted with CNG kit go on for more than a lakh kilometres without any problem. So I dont think you have much to worry about this point PROVIDED you get a good, RTO approved CNG kit installed.
Happy savings,
Sam