100% same happened to me on Motorway, when i drove my car on PETROL, it was fine and i went upto 120 km/h. nothing was bad. but as soon as i switched to CNG near "SUKHEKHI" , the darkest hour started as i was with my family. car stopped, with smoke like "RAIL ENGINE". i thought i had not checked the engine oil and its all gone now. my ring pistons are gone (as it happened with my motorbike exactly same). but thanks to MOTORWAY police, they helped me though it was too costly but still i admire there help.
i changed the PCV valve but now i dont floor full throtle on CNG. and remain at 100 km/h.
This issue is just with PETROL (with me).