What is BS6 ?

BS6 Emission Norms

Scorpio with exhaust smoke
BS6 emission norms created a lot of tense in the automotive industry. BS4 to BS6 has a drastic reduction in emission. Internal combustion engines are one of the main reasons for air pollution. The production of carbon dioxide, carbon monoxide, hydrocarbons, and NOx are the main reasons for bringing strict emission norms. Particulate matters and carbon soot are another bi-product of diesel engine.

Changes made to petrol engines

BS6 petrol engine
Upgrading petrol engines to BS6 was a lot easier. Petrol engines emit far lower PM(particulate matter) and NOx( oxides of nitrogen) than diesel, Hence eliminating the need for expensive hardware’s.  To meet the norms, petrol engines needed bigger catalytic converters that aren’t expensive. However, the problem with this was increased engine back pressure due to which BS6 petrol engines are tuned to have linear power delivery and dull throttle response. 

Changes made to diesel engine

BS6 Ad-blue tank cap
For diesel engines to jump from BS4 to BS6 was a lot of work for the engineers. The BS4 norms went easy on diesel but to meet BS6 norms they needed both Particulate matter and NOx treatment. It needs expensive hardware to reduce 82% of PM emission and 68% of NOx emission

Large diesel engines

Selective catalytic reduction
NOx reduction of all the diesel engines above 2.0-liter is done by selective catalytic reduction (SCR), that injects ammonia based urea also called Diesel exhaust fluid (DEF) into the exhaust. The DEF creates a chemical reaction that converts NOx to harmless nitrogen and water. The SCR technology can achieve NOx reduction of up to 90% but is very expensive, this alone can add ₹1 lakh to the cost of the car. This led to discontinuation of a lot of diesel cars and hence Maruti Suzuki’s bold step to use only petrol.

Small diesel engines

BS6 NOx trap
The more cost effective solution that is used in diesel engines below 2.0-liter engines is the NOx trap. As the name suggests a canister placed downstream of the exhaust manifold traps the NOx. When the canister or trap fills up, a richer fuel mixture is injected into the engine that reacts with the NOx and converts it to nitrogen.

What about bikes ?

BS6 fuels and total reduction in emissions

BS6 emission changes
As BS6 engines have filters and exhaust treating chambers. BS4 fuels with higher Sulphur content have the potential to poison  these systems and might have adverse effects on their operations. Hence running a diesel engine with BS6 diesel is important. BS6 Petrol uses better engines and components designed to achieve lower emissions, hence BS6 petrol can operate safely with BS4 fuel as there is no risk of Sulphur poisonings.  
The BS6 engines have 25% NOx reduction in petrol but diesel engines are cleaner than ever with 82% reduction in particulate matter emission, 68% reduction in NOx emission and 43% reduction in hydrocarbon. 

Image Credits:
TVS motors
Maruti Suzuki
Fuel logic Uk

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