1.  Module I
 Module goals
 How NOx is created
 How temperature affects NOx
 How compression affects NOx
 How EGR affects NOx
 How A/F ratios affect NOx
 Post combustion controls to reduce NOx
 How cats reduce NOx

2.  Vehicle emissions have been controlled since
PCV systems were introduced in 1961
 Early exhaust diagnosis was done using CO &
HC
 Later 02 & C02 was used

3.  NOx was associated as a key player in the
production of photo chemical smog in the late
60’s
 Efforts to reduce CO & HC caused NOx to
increase
 Module 1 addresses NOx
 Formation
 Control

4.  The internal combustion engine is a large air
pump
 Oxygen = 20% = small amount of what is
drawn into the engine
 Nitrogen = 80% = Large amount of what is
drawn into engine
 Plus a very small amount of inert gas
 As an engine wears NOx forms

5.  Two ways to control NOx
 Precombustion
 Before combustion
 Post-combustion
 After combustion

6.  Precombustion controls
 Keeps combustion chamber temperatures below 2500
degrees Fahrenheit
 Lower compression ratios
 Less compression = less heat
 Richer A/F ratios
 More fuel = less heat
 When A/F ratio reaches 16:1 NOx decreases (lean misfire)
 EGR systems lowers combustion temperature.
 Computer Programming
 Retarded timing
 Richer A/F ratios

7.  Post-combustion controls
 After combustion
 Three way Catalytic Converters
 Catalytic Converters are a secondary method
only – they will not overcome excess NOx
created by the engine.

8.  Ignition timing
 Initial & total
 EGR system
 Must pass functional test
 Fuel octane
 Low burns too fast and tends to explode!
 Air intake temperature
 Air duct or cooling systems problems
 Carbon buildup
 Increases compression
 Hot spots
 Air pump operation
 Must divert
 Dirty fuel injectors
 Restricted or bad pattern
 Lean engine operation
 Lean = heat, lean fuel mixture burn too slow!

9.  Other early precombustion systems
 Spark control -- controls timing advance
 TAC -- preheats intake air when cold
 EGR -- recirculates exhaust gasses to lower
combustion chamber temperatures
 EFE -- heats intake manifold

10.  Combustion chamber carbon treatment
 Run additive through engine to burn off carbon
 NOx diagnosis = think what will cause heat