CNG for automotive use has interesting physical and thermodynamic characteristics, in terms of quality and cleanliness of combustion and safety of use. The gaseous state of methane and its high speed of diffusion in the air make it easy to obtain excellent carburation even in the initial phases of operation with a cold engine. This circumstance, together with the fact that, compared to petrol engines, methane emissions upstream of the catalytic converter are considerably lower, accentuates the benefits of using natural gas vehicles in city centres, where cold starts, short journeys and slow running in columns are particularly frequent; conditions which do not allow the engine and catalytic converter to reach ideal operating temperatures quickly.
