BS-VI Tech vs BS-IV: How Different Are The New Emission Norms?

Here’s why diesel vehicles will become far more expensive than petrol once the new BS-VI emission norms come in.

India shifts to Bharat Stage VI emission norms (Euro 6) by April 2020.

Photo: The Quint

From 1 April 2020, all cars, two-wheelers, three-wheelers, buses and trucks sold in India will have to meet the country’s stringent emission standards: Bharat Stage 6 or BS-VI / BS-6. This is equivalent to Euro 6 emission standards that are already in place in many countries since 2015.

India is leap-frogging from BS-IV emission standards directly to BS-VI to become at par with the developed world in emission norms and battle rising pollution levels in many Indian cities.

That doesn’t mean that by April 2020, all other vehicles will have to be off the road. Vehicles that adhere to BS-III / BS-IV emission standards can continue to ply as long as they have a valid registration (of 15 years). Diesel vehicles in the Delhi-NCR region will be allowed to ply for only 10 years, in a bid to reduce the number of diesel vehicles on the road.

How Are BS-6 Norms Different From BS-4?

Bharat Stage VI emission norms drastically reduce the number of pollutants from vehicular exhaust, compared to the current Bharat Stage IV norms. While the difference in emission levels is not that drastic for petrol engines, it is significant for diesel vehicles.

The nitrous oxide emission levels (responsible for acid rain) will drop by 25 percent in the case of petrol vehicles and 68 percent for diesel vehicles. Particulate matter emissions, which is the main concern among diesel vehicles in Delhi, will come down by 89 percent for BS-6 diesel vehicles.

In addition, all vehicles will have real-time monitoring of emissions. All vehicles will have on-board software and OBD (on-board diagnostic) ports to be able to monitor emission levels and give out warnings.

The changes are not related to just vehicles. Fuel quality will also have to be changed, with low-sulphur petrol and diesel being introduced to meet BS-6 norms. Petrol will have to meet a minimum octane rating of 91 RON (which even BS-4 petrol meets).

What New Tech Is Required For BS-6 Petrol Vehicles?

The reason why many car manufacturers in India are already rolling out BS-VI compliant petrol models, but holding back on diesel is because the changes for petrol engines aren’t much.

All BS-IV petrol vehicles were already fuel-injected, which is a primary requirement to meet BS-VI also. The main change is to the sensors used. A BS-VI petrol engine will require faster oxygen sensors and better injectors that can deal with low-sulphur fuel.

Some gasoline-direct injection (GDI) turbo-petrol engines will also have a particulate filter in the exhaust system, while most will have changes to the ignition timing to ensure cleaner combustion. This will help reduce NOx levels.

Bharat Stage 4 and Stage 6 emission norms compared.Photo: The Quint

What New Tech Is Required For BS-6 Diesel Vehicles?

Getting a BS-IV diesel engine to comply with BS-VI emission norms requires major changes to the hardware and layout of a diesel engine. Small capacity diesel engines will have to be fitted with a diesel particulate filter (DPF) to reduce particulate matter emissions (PM levels).

In addition to bring down the NOx levels, small diesel will require a second catalytic converter or selective catalytic reduction (SCR) to break down nitrous oxides into nitrogen and water vapour. These are sometimes called Lean Nitrous Traps (LNT).

Larger diesel engines achieve NOx reduction by urea injection. Here a separate tank with a urea chemical solution like Ad Blue, is injected into the exhaust gases to break them down.

Vehicles will need more space under the bonnet (hence it is difficult to package BS-6 diesel engines in small cars) with the addition of these components. And the cost increase is nearly 20 percent over conventional diesels, as LNTs and DPFs are expensive.

Diesel emission standards compared - BS-4 vs BS-6.  Photo: The Quint

Can I Run My BS-6 Vehicle With BS-4 Fuel?

In 1998, when India was shifting to unleaded petrol, vehicles came with catalytic converters. However, unleaded petrol was not available everywhere, and using regular petrol then, lead to many vehicles damaging their catalytic converters. Does such a worry exist when running a BS-6 vehicle with BS-4 compliant fuel?

Not quite. BS-6 vehicles can safely handle BS-4 compliant fuel. The only thing is the emissions from the tail-pipe will not be BS-6 level compliant. BS-4 fuel has 50 ppm sulphur content, which will be reduced to 10 ppm in BS-6 level fuel.

This means there will be higher particulate emissions likely, which can quickly clog up the particulate filter especially in diesel vehicles.

Can I Run My BS-4 Vehicle with BS-6 Fuel?

What happens post 2020, when most of India shifts to BS-VI standard fuel? Is it possible to run your old BS-IV vehicle with BS-VI grade fuel? Here too there are advantages and disadvantages.

The clear advantage is that the fuel will be of a higher quality and hence cleaner. However, petrol and diesel will also have lower sulphur content. Sulphur has lubricant properties for injectors and in-line fuel pumps.

While BS-VI compliant cars are built to handle low sulphur levels, BS-4 vehicles may need to use a lubricant additive in the tank to ensure that expensive parts like fuel injectors don’t get prematurely worn out.