You can convert your Sunny XL petrol to CNG easily from any of the reputed aftermarket fitment store. The warranty for the car has already expired and there won’t be any issue with the practicality of the car as you can have nearly 300 liters of boot space left after the fitment of CNG kit. Nissan may launch an official CNG fitted Sunny in the coming time but it is easy to have a kit from other stores as they will sell the same at nearly half the price of that by the official store. You should go for a sequential CNG kit as it minimizes the performance alteration as computer controlled gas injection retains the overall performance of the car.