Page 268 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

• Air injection with catalytic converter: A catalytic converter with air injection is a type of emission control
system used in vehicles. It injects air into the exhaust system before the catalytic converter to help burn
off harmful pollutants more efficiently, reducing emissions. This system aids in meeting stricter emissions
standards and improving air quality.
1 Selective catalytic reduction (SCR): Selective catalytic reduction (SCR) is the process by which oxides
of nitrogen (NOx) contained in diesel exhaust are reduced to nitrogen (N ) and water (H O)
2
2
2 Selective catalytic reduction
SELECTIVE: targets NOx in diesel exhaust
CATALYTIC: requires a catalyst
REDUCTION: NOx is reduced to nitrogen (N )
2

SCR requires diesel exhaust fluid (DEF) - a urea based solution
SCR reduces NOX emissions up to 93%.

Selective catalytic reduction (scr) system components
• Diesel exhaust Fluid (DEF)
• DEF injector
• Mixing tube
• SCR catalyst

1 Working principle of SCR system: SCR works by injecting diesel exhaust fluid (DEF), into the hot exhaust
stack. DEF works in conjunction with the hot exhaust gases and catalyst to break NOx into two components
of our normal atmosphere wair vapor and nitrogen.

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CITS : Automotive - Mechanic Diesel - Lesson 80 - 83