dont do it dude..firstly,if u install another cylinder,there wont be no space left to see whats comin at ur back of car! plus its already risky to have one cylinder in,let alone talkin about 2nd..
i guess,petrol py setting krwa he laen bhai,in winter,cng is goin to be a problem,and in comin future,this is gonna get worse..so instead of wasting more money on cng,save money for petrol..or u can always buy a motorcycle!