The problem with diesel

Headline : The problem with diesel

Details :

Context

• Automakers in India in the recent times have started moving away from diesel cars value chain.
• The proportion of diesel cars in the total passenger vehicles sales has decreased from 48% in 2012-13 to 22% in 2018-19.

 

Reason

Decrease in price differential

• The price differential between petrol and diesel has reduced substantially after the deregulation of diesel prices in 2014.

 

Introduction of BS VI norms

• India is leapfrogging from BSIV to BSVI with 13 cities adopting BS VI norms starting this year and the entire country switching to BS VI fuel by April 2020.
• The technological changes needed in a diesel engine are more complicated when compared to petrol engines.
• As a result diesel cars will be prohibitively expensive.

 

Constraint on Oil Makers

• The transition to BS IV took 7 years for oil refiners to start producing better fuel.
• Thus the ability of oil refiners to produce enough quantity of high-grade dieselin accordance with BS VI standards is questioned.

 

Design constraints for Indian roads

• The new-gen vehicles to meet the BS VI standards require the following technology upgrades:
  • Diesel particulate filter
  • Selective catalytic reduction system
  • Lean NOx trap
• However the slow speeds on Indian roads makes it difficult for carrying out design changes with these critical components.
• For instance the diesel particulate filter has a system to burn soot produced in the emissions.
• This requires temperatures of around 600 degrees Celsius which is difficult to achieve at low speed driving on Indian roads.

 

In brief: BS VI Norms

• Bharat Stage VI (BS VI) is an emission standard that will induce technology in the vehicles to reduce pollutant emissions.
• The vehicles will mandatorily include OBD (On-board diagnostics) which will monitor the pollution caused by the vehicle in real time.
• The BS-VI vehicles use selective catalytic reduction technology which substantially reduces particulate matter emission.

 

Specification of BS-VI norms for diesel engines

• BS-VI grade fuel contains 10 parts per million (ppm) of sulphur as against 50 ppm in BS-IV fuels.
• 10-20% reduction in particulate emission when used in BS-IV or lesser grade engines.
• The Octane number for petrol engines – 91 under BS-VI emission norms. (BS II – 88)
• The PM emission in diesel engines – 80% reduction
• NOx emission in diesel engines – 68% reduction.

 

Diesel Engine Emissions

• Incomplete combustion of diesel results in carbon monoxide, hydrocarbons and aldehydes.
• The characteristic smell of the diesel is due to hydrocarbons and aldehydes.
• High temperature and pressure inside the engine gives rise to Nitrogen oxides including nitric oxide (NO) and traces of nitrogen dioxide (NO2).
• Sulphur present in diesel gives rise to Sulfur dioxide (SO2) upon combustion.
• Particulate matter includes soot, aromatic hydrocarbons, and hydrated sulfuric acid.

 

Selective catalytic reduction system

• SCR systems are emissions control system that injects a fluid through a special catalyst into the exhaust stream of a diesel engine.
• The fluid used is usually a reducing agent like urea that converts nitrogen oxides into nitrogen and water.
• Thus SCR technology is used to reduce NOx emissions in diesel engine.

 

Diesel particulate filter

• Diesel particulate filter is a filter that captures and stores exhaust soot to reduce particulate matter emissions from diesel engines.
• If the soot is trapped inside the filter it gets clogged.
• As a result the filter is regenerated by burning the soot particles at the exhaust pipe.
• The soot is burnt at high temperatures of around 600 degree Celsius which is obtained by the temperature of the exhaust gas itself.
• This regeneration process burns off the excess soot deposited in the filter, reducing the harmful exhaust emission and thus reduces the black smoke seen in diesel vehicles.