What Is BS6 Engine?- Norms And How Does it Work

What is BS6 Engine?

BS6 emission standard is the sixth emission norm in the sequence in terms of reducing pollution as compared to retiring the BS4 emission standard. BS4 and BS6 are the assigned emission norms that set the maximum allowable levels of pollutant releases from a motor vehicle engine exhaust.

“BS” refers to Bharat Stage, which is an emission measuring yardstick for all the vehicles plying on the Indian roads. The BS emissions are decided by the Central Pollution Control Board under the helm of the Ministry of Environment, Forest and Climate Change.

The Bharat Stage 6 (BS6) is a stage of emission control set by the CPCB after a slew of stages, with the first standard coming in the year 2000, named ‘India 2000’, followed by BS2 and BS3 in the year 2005 and 2010 respectively. The current BS4 standards came into effect in 2017, after a long gap.

To fill up the time wasted for the long gap of seven years and in an attempt to reduce pollution standards the Government decided to take a long jump to BS6 while skipping BS5 completely.

BS6 vs previous emission norms

With every different stage, comes a few changes in the manufacturing of the vehicles and the emission standards. Here are a few changes that came in the past before BS6.

BS1 (Bharat Stage 1)

It was the first stage to be formulated based on European Standards or the Euro 1 norms and was rolled out in 2000. The emission standards were also known as ‘India2000’.The Bharat Stage 1 required the manufacturers were required to retune the carburettor, the secondary air intake system, exhaust gas reconciliation system and a lot more.

BS2 (Bharat Stage 2)

The BSII norms came into place in the year 2000 and the sale lasted till 2010. Multi-Point fuel injection had to be included by replacing the carburettor. The BS2 norms were considered to be successful keeping in mind the fact that during this period the emissions were reduced quite significantly.

BS3 (Bharat Stage 3)

The Bharat Stage 3 emission norms came into effect in the year 2005, with the sale of the vehicles made mandatory after the year 2010. The BS3 emission norms in the vehicles led to lower emissions in petrol vehicles.

BS4 (Bharat Stage 4)

The Bharat Stage 4 emission norms came in after a long wait in the year 2017. The newer norms required the manufacturers to add a bigger catalytic converter to minimize nitrogen-based emissions while also bringing a small change in the Engine Control Unit of the vehicles to ensure efficient combustion.

BS6 (Bharat Stage 6)

The Bharat Stage 6 (BS6) will bring down and restrict the emissions from the tailpipe to 1.0g/km of Carbon Monoxide. The BS6 fuels will have a lesser amount of sulfur in it and involve more additives. The BS5 emission norms were skipped by the standard body to curb pollution by bringing in stricter norms.

BS6 Engine

What are the advantages of using BS-6 compliant cars?

In the Indian urban areas, vehicle pollution is one of the major contributors to the worsening of air quality. Studies have shown that the release of SO2, CO2, NOx, and other particulate matter harms the health of Indians. The BS6 vehicles are over 50% less polluting than the BS4 vehicles.

With the BS-6 standards, the NOx emission rate can come down by approximately 25% in the case of petrol engines and 70% in the case of diesel engines. The cancer-causing particulate matter emissions from the diesel engines will also come down by 80%.

The major objective of the BS-6 engines is to reduce the sulphur content in emission, as the intake of sulphur is very harmful to health (especially cause’s respiratory issues) in the long term. BS 6 fuel has lower sulphur content than BS-4 fuel.

Some of the advantages of using BS-6 engines are:

  • it is eco-friendly
  • it is more refined
  • more cleaner
  • decreases the atmospheric pollution and improves the air quality
  • it is equipped with fuel infusion resulting in better throttle response & fuel efficiency
  • It mandates the installation of Selective Catalytic Reduction (SCR) technologies and Diesel Particulate Filters (DPF) inside the engine to reduce the emission of soot from the vehicle.
  • OBD (on-board diagnostics) and RDE (Real Driving Emission) is the mandatory feature for all the BS-4 vehicles, and they are used to monitor the real-time emission from the exhaust gases of the vehicle.
  • BS-4 fuels contain 50 parts per million (ppm) sulphur, but the BS-6 grade fuel consists of only 10 ppm sulphur content.

How does a BS6 engine work?

The BS6 engines work on the account of the Selective Catalytic Reduction unit, which is an advanced emissions control unit developed by the manufacturers to control emissions in a car using a reductant agent which is usually automotive-grade urea.

In Bharat Stage 6, (BS6) the SCR unit converts NOx (Nitrogen Oxide) into two harmless particles i.e. diatomic nitrogen and water using AdBlue or diesel exhaust fluid. The diesel fluid is made of urea and deionized water.

When exhaust gases from the engine come in contact with the AdBlue, the urea gets converted into ammonia and carbon dioxide and the ammonia later converts the gases into nitrogen and water vapour, thereby reducing pollutant emission from the engine.

What is an SCR?

The SCR or Selective Catalytic Reduction unit is a specially designed component in a BS6 engine, which is added to reduce emissions.

The SCR system reduces NOx emissions by increasing the combustion temperature, which reduces the production of Particulate Matter in the engine. The NOx although increases while doing so, but it is controlled by the SCR using catalytic reduction.

How is SCR beneficial?

The SCR is beneficial as it increases fuel efficiency to some extent and provides better power. With the inclusion of an SCR in the engine, the maintenance period is reduced and the life of the engine is increased.

The urea solution which is dosed into the fuel pump is suitable for the Indian climatic conditions and can be used to reduce the pollutants emitted from the cars.

What is Adblue?

AdBlue is the trade name for a type of diesel exhaust fluid. It’s a mixture of urea and deionised water that’s stored in a separate tank from the car’s fuel. When the car’s engine is running, tiny amounts of AdBlue are squirted onto the exhaust gas produced, turning the NOx into nitrogen and water.

It is a diesel exhaust fluid used in vehicles with Selective Catalytic Reduction (SCR) technology to reduce harmful gases being released into the atmosphere. AdBlue is a 32,5 % solution of high-purity, synthetically manufactured urea in de-mineralized water. It is a safe-to-use fluid.

How AdBlue works?

Vehicles with SCR technology have a separate tank filled with AdBlue. This is then injected into the exhaust pipe, in front of the SCR catalyst, downstream of the engine.

Heated in the exhaust, it decomposes into ammonia and CO₂. When the NOx from the engine exhaust reacts inside the catalyst with the ammonia, the harmful NOx molecules in the exhaust are converted to harmless nitrogen and water, which are released from the tail pipe as steam.

Will BS6 fuel be more expensive?

As of now, BS6 fuels cost the same as BS4 fuel in Delhi and other metro cities. But the refinement process and the up-gradation of refineries to churn out BS6 fuel might impact the fuel prices. So, it’s safe to expect a hike in fuel prices as time marches forward or once the norms come into place.

Will BS6 increase mileage?

Yes. In layman terms, a BS6-compliant engine will be more restricted in comparison and will thereby result in a minor drop in power and efficiency. For example, the Maruti Suzuki Dzire with the 1.2-liter BS6-compliant petrol engine is claimed to return 21.21 kmpl.

What are BS-VI norms?

The central government has mandated that vehicle makers must manufacture, sell and register only BS-VI (BS6) vehicles from April 1, 2020. The first emission norms were introduced in India in 1991 for petrol and in 1992 for diesel vehicles.


  • BS6 emission standard is the sixth emission norm in the sequence in terms of reducing pollution as compared to retiring the BS4 emission standard. BS4 and BS6 are the assigned emission norms that set the maximum allowable levels of pollutant releases from a motor vehicle engine exhaust.
  • The BS6 norms vehicles required to emit nearly 60mg/km of NOx (nitrogen oxides) emission, not more than that. Whereas, it was 80mg/km in the case of BS4 norms. Though, the particular matter (PM) limit has also been capped at 4.5mg/km in petrol engines.
  • In the case of diesel cars emission norms, it’s way strict. NOx emissions should go down from 250mg/km to 80mg/km, HC+NOx emission must go down from 300mg/km to 170mg/km, PM emissions from 25mg/km to 4.5mg/km.
  • The level of sulphur and nitrogen oxide content in fuel plays a significant role. BS6 fuel has lower sulphur content than BS4 fuel. The sulphur content in BS6 fuel is five times lower (10ppm) as compared to sulphur content in BS4 fuel (50ppm). And, the nitrogen oxide level for the BS6 diesel engine and petrol engine will be brought down by 70% and 25%.
  • After BS6 norms come in effect from 1st April 2020, BS6 fuel will start dispensing across all petrol pumps in the country. You can even use BS6 fuel in BS4 or older cars without any trouble.
  • Sulphur in fuel helps in proper lubrication inside the engine and burn more efficiently. BS6 contain lower sulphur than BS4 fuel with additives that imitate the lubricating properties of Sulphur.
  • Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) came up with a role in BS6 norm, whereas, it wasn’t available with BS4.
  • With the introduction of BS6 emission norms, Real Driving Emission (RDE) will also be implemented to measure a vehicle’s pollutant emission in real-time conditions. It was not paired with BS4 emission norms.
  • Onboard Diagnostic (OD) feature is another change that came up with BS6. It wasn’t introduced with BS4.
  • A vehicle that has BS6 compliant engine require to fill with BS6 fuel. It won’t adhere to BS6 norms if someone with a BS6 engine uses BS4 engine fuel. Whereas, the emissions will be increased if a vehicle with BS4 fuel engine uses BS6 engine fuel.