The diesel engines also have better combustion as they operate with excess air, low energy and with higher compression ratio. One more reason to favour diesel engine is the new particulate filter first introduced by PSA Peugeot Citroen which were also adopted by other companies like Toyota.

Moreover, when the engine becomes old, the emission output is more in the petrol engines compared to the diesel ones. Now the Fiat is working on a new project called NZEV (Near Zero Emission Vehicles). Fiat has also started their project on common rail direct injection system. Engines that will be free from oil change are under trail. This work was already achieved by Mercedes-Benz that is ten times better than the technology that was used decades back. There are diesel direct injection engines available in the market where the oil change is needed only after 40,000 km compared to the petrol version, where oil change takes place between 14,400 km and 20,000 km.