Talk given in at the Joint Research Centre, Ispra, Italy, December 2009.
1. Institute for Environment and Sustainability 1
Joint Research Centre (JRC)
Modelling of diesel-engine exhaust
nanoparticle dynamics
L. Isella, B. Giechaskiel, Y. Drossinos
IES - Institute for Environment and Sustainability
Ispra, Italy
http://ies.jrc.ec.europa.eu
http://www.jrc.ec.europa.eu
2. Motivation and Goals
Institute for Environment and Sustainability
• Diesel-generated nanoparticles raise concerns about their effects on
human health and environment.
• Legislation regulating diesel-vehicle particulate mass emissions
(EURO1,2,3,4,etc. . . ), but particle number distributions may be a
better metric (especially for health effects).
• Evaluate effect of sampling and experimental conditions on
measured particle number distributions emitted from light/heavy duty
vehicles ⇒ PMP.
• Exploratory research as an experimental and theoretical study of the
dynamics of non-volatile (PMP) particles emitted from diesel
light-duty vehicles (emphasis on nanoparticle agglomeration).
• Experiments performed at the Vehicle Emission LAboratories
(VELA) at Ispra.
3. Experimental set-up
Institute for Environment and Sustainability
• Temperature and particle number distribution measurements along
whole experimental manifold (not only at legislated position).
6. Aerosol in a Tube
Institute for Environment and Sustainability
z = Um τ
Diffusional
ExhaustCarrier Agglomeration losses (vdif)
Flow
Kij
Monomers
Um
R
Thermophoretic
∆T
losses (vth)
• Four different aerosol processes: agglomeration, diffusion,
thermophoresis and convection.
• 1D model neglecting turbulence-induced local particle density
inhomogeneities.
• nq (flux-averaged axial aggregate concentration of size dq [q-mer])
along tube as function of residence time τ
q−mer creation q−mer removal
dnq (τ ) 2(vdif + vth ) 1
=− Kij ni (τ )nj (τ ) −nq (τ ) Kiq ni (τ ) .
nq (τ ) +
dτ R 2
i+j=q i
diffusion and thermophoresis
agglomeration
7. Time-Scales and Approximations
Institute for Environment and Sustainability
103 s, τth
• Time-scales for each process: τagg 2s, τdif 30s and
2s.
τconv
1.4 × 108
Simulation
q
Outlet measurement
q
q
q
Residence time for
1.18 × 108
q
a 6.5m long transfer tube
q
q
N[cm−3]
q
q
q
q
9.6 × 107
q
q
q
q
q
q
Final concentration for a q
q
6.5m long transfer tube (LAT) q
q
q
Final concentration for a
7.4 × 107
9m long transfer tube
(VELA)
0.0 0.5 1.0 1.5 2.0
τ[s]
• Effect of the transfer tube length on number concentration: important
for experiment reproducibility.
• Transfer tube length should be regulated.
• Different τagg ∝ 1/N∞ (0) for a light-duty Euro4-5 diesel engine.
8. Langevin Equation
Institute for Environment and Sustainability
m1
Random kicks from air molecules
Brownian motion and nanoparticle diffusion (fluctuation) W
Push monomer through air
Friction (dissipation) β1
Interaction force F between monomers
• 3D system of interacting monomers, each obeying
m1¨i = Fi −m1 β1 ri + Wi (t) .
˙
r
force friction noise
10. Final Remarks
Institute for Environment and Sustainability
• Exploratory research beneficial to on-site experimental activities
(VELA).
• Strengthening of JRC scientific reputation by addressing topical
issues in diesel-vehicle particulate emissions.
• Recommendation for policy makers ⇒ transfer tube length to be
regulated.
• Debate whether to regulate light/heavy duty emitted diesel particle
number distributions in the future ⇒ timeliness of the exploratory
research.