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.
Section : Environment & Ecology

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