There's nothing wrong with using CNG in a bigger engine, or a smaller engine. CNG is cleaner and does no harm to the engine if the engine is tuned right. Be sure to run the car atleast 10kms on petrol after every 100kms run on CNG. The thing is, we love to abuse priviliges granted to us, same is the case with alternate fuels. The world is looking towards alternate energy sources and we laugh at each other. Do you know what a methanol based race fuel is? These were used in Indy cars and monster truck racing, and guess what it was made up of? Methane, aka natural gas. Ethanol, Bio ethanol, Methanol, Bio Diesel, Alchohol fuel, Butanol fuel, Nitro Methane are all alternate fuels being used on roads and tracks all over the world. And we laugh...
About CNG
Around the world, this gas powers more than 5 million vehicles, and just over 150,000 of these are in the U.S. American usage is growing at a dramatic rate.