Module 2: Genesis and Mechanism of Formation of Engine Emissions
Lecture 3: Introduction to Pollutant Formation
Engine emissions
SI engine vehicles without emission control have three sources of emissions
Exhaust emissions
:
Almost all of 100% of NOx and CO, and 60% of HC are emitted through the engine exhaust or vehicle tailpipe
Crankcase emissions
:
About 20% of HC are emitted via crankcase blow by gases
Evaporative Emissions
:
Fuel evaporation from tank, fuel system, carburettor and permeation through fuel lines constitute another 20% of total HC
CI engines on the other hand release all of harmful emissions into atmosphere through its exhaust gases
Typical Exhaust Emission Concentrations
SI Engine (Gasoline fuelled)
Depending upon engine operating conditions without catalytic control engine out emissions range :
CO
:
0.2 to 5% by volume (v/v)
HC
:
300 to 6000 ppmc1*, v/v
NOx
:
50 to 2000 ppm, v/v
*ppmc1= parts per million as methane measured by Flame Ionization Analyzer/Detector(FIA or FID)
CO emissions are high under engine idling and full load operation when engine is operating on fuel rich mixtures. HC emissions are high under idling, during engine warm-up and light load operation, acceleration and deceleration. NOx are maximum under full engine load conditions.
CI (Diesel) Engines
Diesel engines usually operate with more than 30% excess air band the emissions are accordingly influenced.
CO
:
0.03 to 0.1 %, v/v
HC
:
20 to 500 ppmc1
NOx
:
100 -2000 ppm
PM
:
0.02 to 0.2 g/m3 (0.2 to 0.5% of fuel consumption by mass)
