Emissions

Question 1

Distinguish between raw and vehicle emissions

Answer 1

raw emissions: engine exhaust emissions without aftertreatment
vehicle emissions: vehicle exhaust emissions with afertreatment

Question 2

Name the toxic components of typical exhaust gases of an ICE

Answer 2

Toxic components (1%)

• CO
• NOx
• HC (unburned)
• particulate matter

Question 3

Briefly explain why HC-emissions can typically found near the cylinder surface

Answer 3

Wall is cooler than flame and does not heat up as quickly-> quenching, HC do not get burned
emissions F11

Question 4

Name and briefly explain the characteristics of CO-emissions

Answer 4

characteristics:
- highly toxic
- colourless, odorless, gaseous
Formation
- rich mix: incomplete comb. , no complete oxidation to CO2
- lean mix: cycle cycle variation, quench of flame front at cyl. wall

Question 5

Name and briefly explain the characteristics of HC-emissions

Answer 5

Characteristics:
- irritation of lungs and eyes
- promotes atmosheric inversion
- Different types: aldehydes, un/saturated, aromatics
- colour: blue or white smoke
formation:
- Quench at cyl. wall or fireland volume
- piston top
- inhomogenous mixture
reduction possibilities:
- small boundary layer: high pressure, high gas temps., high cyl. wall temp, large amount of in-cyl. turbulence

Question 6

Name and briefly explain the characteristics of NOx-emissions

Answer 6

NO
- 90% of NOx
- colourless
- reaction with air to NO2
NO2
- 10% of NOx
- Colour red/amber
- strong acid smell, strong respiration problems
N2O(lachgas)
- very small amounts
- GHG potential factor 298
formation
- high pressures and temps.-> most NOx formed in premixed comb. phase
- lean mixtures(oxygen) N2+O2=2NO
- no reverse reaction under 2200K, enditherm

Question 7

Name and briefly explain the characteristics of Soot-emissions

Answer 7

Ruß

Question 8

Explain the objective of emission legislation and the typical constraints

Answer 8

• Goal is to reduce emission of pollutants of internal comb. engines by setting quantitative limits.
  typical constraints
  Gasoline (Euro6): 1g/km CO; 0,1g/km HC; 0,005g/km PM
  Diesel: 0,5g/km CO; 0,08g/km NOx; 0,005g/km PM

Question 9

Show, using a diagram, the typical graphs of NOx, HC and CO emissions of SI-engines

Answer 9

Emission F33

Question 10

Where are HC emissions mainly formed?

Answer 10

Major sources of HC-emissions in SI-engines

• Piston ring pack crevices
• Vavle seat crevice
• spark plug thread crevice
• cylinder head gasket crevice
• lubricating oil, absorption, desorption
• bulk quenching within flame front for lean mix and high turbulences

Question 11

Show, using a diagram, the typical graphs of NOx, HC and CO and soot emissions of CI-engines

Answer 11

emission F37

Question 12

How can NOx emissions in general be reduced?

Answer 12

NOx formation can be reduces by decreasing the flame temp

• delay combustion into expansion phase
• exhaust gas recirculation (EGR)-> interna l(valve overlap), external (exhaust gas in comb. chamb.)
• lower compression ratio
• cool the air charge going into the cyl.
• aftertreatment

Question 13

Briefly explain the typical exhaust gas aftertreatmentfor SI and CI engines

Answer 13

SI-engine:
- conversion of HC, CO, NOx required
- conversion rate depends on comb. air ratio(lambda=1) F43!
- three-way catalytic converter
# an oxidazing reation converts CO and unburned HC
# reduction of NOx to produce CO2, N2, H2O
CI-engine
- Three-way cat. can not be uses: lean mix with lambda>1
# Oxi-Catalyst for Co, HC
# SCR-Catalyst for NOx reduction