Emission Control and Environmental Aspects
What the exam tests
Emission control and environmental aspects covers pollutants, Bharat Stage norms, catalytic converters, EGR, DPF, SCR, PCV and evaporative controls. Questions test how each device reduces a specific pollutant.
Core rules and concepts
- Petrol exhaust pollutants include CO, HC and NOx; diesel adds PM. CO arises from rich mixtures; NOx from high temperature and pressure.
- A three-way catalytic converter oxidises CO and HC and reduces NOx, but needs stoichiometric operation and unleaded fuel.
- EGR lowers combustion temperature and reduces NOx.
- A diesel particulate filter traps soot and burns it during regeneration.
- SCR uses urea injection to reduce NOx in diesel exhaust.
- PCV returns crankcase vapours to the intake; EVAP traps fuel vapour from the tank.
Worked example
A catalytic converter reduces CO from 1.2% at the inlet to 0.12% at the outlet. Efficiency = (1.2 - 0.12)/1.2 × 100 = 90%. If the outlet rises to 0.30%, efficiency falls to 75%, indicating catalyst ageing, a misfire or a rich mixture. The calculation links a measured gas reading to a diagnosis rather than simply failing the vehicle.
Traps that cost marks
- Using leaded fuel with a catalytic converter; lead poisons the catalyst.
- Confusing DPF regeneration with normal exhaust smoke.
- Assuming EGR reduces CO rather than mainly NOx.
- Ignoring evaporative emissions from the fuel tank.