Passenger vehicles compliant with Bharat Stage-III emission norms vary widely from their Bharat Stage-IV compliant engines, depending on the size of the car and whether they are petrol or diesel versions. On the outside, the differences are indistinguishable. However they differ in the electronics, sensor system, the engine’s ability to process low-sulphur fuel and their “after-exhaust” system that determines emissions.
The Hindu spoke to experts from multiple car companies, who said that most passenger cars today were designed to comply with BS-IV emission standards. However, many heavy commercial vehicles, if they had BS-III built engines, employed a mechanical fuel pump and used fuel less efficiently. This in turn influenced subsequent emissions of nitrous oxide, carbon monoxide and particulate matter.
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Sulphur content
BS-IV engines also require that the sulphur content of the fuel they use be less than 50 part per million (ppm) whereas BS-III ones can run on 350 ppm fuel. “You cannot retrofit these engines as high sulphur can clog the injectors,” said an expert from a prominent car manufacturer on condition of anonymity. “The passenger cars are not a problem, it’s the heavy vehicles and two-wheelers,” he said.
The Centre for Science and Environment said that the transition can lead to substantial reductions in particulate matter emissions. For instance, from new trucks, the emissions can dip by 80% and from cars by half.
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Dipankar Saha, who heads the Air Quality Division, Central Pollution Control Board, said that a major benefit in the city’s air was unlikely. “There may be more efficient cars around but the growth in cars continues to be high and that will not improve the air quality,” he said.