How BS VI cars work: Two tanks, diesel in one, AdBlue in the other

BS VI emission norms will be introduced in India from April 2020 in order to reduce pollution caused by vehicles. However, unlike earlier norms, introducing BS VI norms won't be that easy. Car makers introduced CRDI or common rail direct injection (CRDI) technology when India implemented BS III emission norms way back in 2005. The CRDI technology gave a new lease of life to small diesel engines that were crude and less powerful. But the changes that are going to come with BS VI is not something similar to what had happened to diesel engines in 2005.

The new norms could lead to an increase in the cost of diesel cars and perhaps make them less popular with buyers. This should be seen along with the statements of several car makers who have announced that they will stop production of even small diesel engines.

In order to reduce emissions, diesel vehicles will have to be fitted with a selective catalytic reduction (SCR) system, and components like diesel particulate filters (DPF). Moreover, like engine oil, it will need regular refilling of diesel exhaust fluid also known as AdBlue.

What is diesel exhaust fluid?

The SCR is used to considerably reduce the amount of dangerous nitrogen oxides emitted by diesel engines. The SCR converts nitrogen oxides into two harmless products – water vapour and nitrogen. The SCR uses the diesel exhaust fluid or AdBlue to reduce harmful NOx emissions.

AdBlue is composed of 62.5% de-ionised water and 37.5% urea. When AdBlue meets a hot exhaust gas, the urea is converted into ammonia and carbon dioxide. When the ammonia encounters the catalytic elements inside the SCR core, it reacts with the NOx in the exhaust stream. The reactions that take place convert the NOx into water and nitrogen.

At present, all heavy vehicles use diesel exhaust fluid. In small vehicles, AdBlue will be kept in small tanks of up to 10 litres' capacity. The only car that currently uses a BS VI diesel engine is Jeep Compass Trailhawk. The diesel exhaust fluid tank in the Trailhawk has a capacity of 13 litres.

AdBlue, which is sold only through dealerships, costs Rs 127 for a litre. However, when BS VI vehicles become common, the price could come down. A full tank could help cover 6,000 km to 10,000 km. Without diesel exhaust fluid, a BS VI diesel vehicle can't be turned on.