Before understanding the difference between BS4 and BS6-compliant engines, we will first have to understand how an engine works. After that, we will learn about BSES (Bharat Stage Emission Standards) which regulates emissions of regular vehicles like cars and Bikes. 

Why BSES has stopped BS4-compliant engines and made BS6-compliant engines mandatory for each vehicle and implied it on 1st April 2020. 

So In this article, we will understand how an engine works, and what is BS4 and BS6 engines. The difference between their performance and the norms of pollution emission on the basis of BS4 and BS6.

Who is BSES

Bharat stage emission standards (BSES) are emission standards instituted by the Government of India to regulate the output of air pollutants from internal combustion engines and Spark-ignition engine equipment, including motor vehicles.

The standards and the timeline for implementation are set by the Central Pollution Control Board under the Ministry of Environment & Forests and climate change.

The standards, based on European regulations were first introduced in 2000.

How does an engine work?

Basically, in an internal combustion engine (or ICE for short), the fuel is ignited and burned right inside the engine itself. The engine then uses that energy to do work, like making your car go.

The engine is made up of a fixed cylinder and a moving piston. When the fuel burns, the gases produced push the piston, which then rotates the shaft. This motion is ultimately what drives your car's wheels via a system of gears in the powertrain.

There are two main types of internal combustion engines out there: the spark ignition gasoline engine and the compression ignition diesel engine. Most of them are what's called "four-stroke cycle" engines, which means it takes four piston strokes to complete a full cycle.

During that cycle, there are four different stages: intake, compression, combustion and power stroke, and exhaust. Basically, the engine sucks in air and fuel, compresses it, burns it, and then expels the byproducts (like carbon dioxide, carbon monoxide, and so on) out through the exhaust system.

What is BS4?

So, in April 2017, a set of rules called Bharat Stage IV norms were put into effect all across the country. These rules say that any vehicle made or sold after April 2017 has to meet certain standards called BS IV.

Basically, this means that vehicle registration authorities can't register any vehicles that don't meet these standards. And what are those standards, you ask? Well, under the BS IV rules, vehicles can only have 50 parts per million of sulfur content, which is way less than the 350 parts per million allowed under the older BS III rules.

Plus, the amount of nitrogen oxide, hydrocarbon, and particulate matter emissions have all been reduced a lot under the new rules. So basically, the BS IV norms are all about making vehicles cleaner and more environmentally friendly.

What is BS6?

The central government has mandated that vehicle makers must manufacture, sell and register only BS-VI (BS6) vehicles from April 1, 2020. 

This important step was taken to control the heavy pollutant emission faced by the people became worse around 2019. The adoption of norm BS6 is introduced to bring down pollution levels.

Under something called the BS6 emission regime, which is a set of rules that started in India recently, the amount of particulate matter (or PM for short) that petrol vehicles can emit has been limited to just 4.5 milligrams per kilometre.

And that's not all – the overall limit for pollution has been greatly reduced under the BS6 rules. 

For example, while diesel vehicles were previously allowed to emit up to 250 milligrams per kilometre of a pollutant called NOx under the older BS4 norms, that limit has been lowered to just 80 milligrams per kilometre under the newer BS6 rules.

What is BS6 2.0?

Did you know that in India, there's a new rule that's all about making cars emit less pollution? It's called the BS6 emission standard, and it was introduced last year in April 2020. Basically, this rule says that cars have to emit lower levels of harmful pollutants like NOx and Particulate Matter.

To make sure that cars are complying with these new rules, car companies have been using either Lean NOx Trap (LNT) or Selective Catalytic Reduction (SCR) technology. That’s why this new BS6 rule called BS6 2.0 that has been introduced on 1st April 2023.

So what's different about BS6 2.0? Well, the big change is that the emissions levels for cars will be monitored in real-time, instead of just being tested in a lab. This means that the actual amount of pollution that a car puts out can vary depending on things like traffic and driving behaviour. But don't worry – these new rules are all about making sure that cars are as clean as possible, and that they're not harming the environment.

With the new BS6 2.0 emission standards, vehicles are going to need some serious upgrades. That means things like particulate filters, selective catalytic reduction, and better engine management systems.

If you've got a diesel engine, you're going to need something called an SCR device, which stands for Selective Catalytic Reduction. Basically, this device uses a special solution called AdBlue to help reduce the amount of NOx emissions that your car produces.

Now, here's the catch – getting all of these fancy new upgrades is going to cost you! If you're buying a diesel passenger vehicle with a BS6 2.0 engine, you can expect to pay a lot more than you would for a petrol car. In fact, the price difference is already pretty big, and this is only going to make it worse.

That's why a lot of people are starting to look at other options, like CNG, petrol, or petrol-hybrid models. It's all about finding the right balance between performance, price, and environmental impact.

What were the previous BS1, BS2, and BS3 norms?

BSI or BS1 Emission Norms

In India, the BS-I regulation imposed stringent limits on carbon emissions, allowing only up to 272 mg per kilometre, as well as a cap on respirable suspended particulate matter discharge at 14mg. Car manufacturers had to adhere to an additional limit of 97 mg per kilometre on the release of Nitrogen Oxides+ and Hydro Carbons.

To comply with the BS-I regulations, automakers were required to make significant adjustments to their vehicles' secondary air intake systems, exhaust gas recirculation systems, and carburettors, and install a tri-metal layer in the system.

BSII or BS2 Emission Norms

The Bharat Stage-II emission norms in India put a cap on the sulphur content in fuels, limiting it to 500 parts per million. To comply with the emission standards, acceptable Carbon Monoxide emissions were set at 220 mg per kilometre, while the maximum allowable respirable suspended particulate matter discharge was 8mg. Additionally, car manufacturers had to ensure that their vehicles met the maximum discharge limit of 5mg per kilometre for Nitrogen Oxides and Hydro Carbons.

To achieve these stringent emission limits, automakers had to ditch the conventional carburettor and instead, equip their vehicles with a more advanced Multi-point Fuel Injection system.

BSIII or BS3 Emission Norms

In 2010, the Indian government made it mandatory for all automobiles to adhere to the BS-III emission norms. According to the BS-III standards, the maximum permissible levels of Respirable suspended particulate matter discharge was capped at 500 mg per kilometre, while Hydro Carbons+Nitrogen Oxide discharge was limited to 35 grams per kilometre. The maximum allowable Carbon Monoxide emission was set at 230 mg per kilometre.

To further reduce emissions, the BS-III norms restricted the sulphur content in fuels to 100 parts per million. Moreover, to meet the emission standards, car manufacturers had to equip their vehicles with a catalytic converter, which could effectively handle Hydro Carbons and Carbon Monoxide emissions.