Talk given in at the Joint Research Centre, Ispra, Italy, December 2009.

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Talk given when receiving the award for the best exploratory research on behalf of the Institute of Environment and Sustainability.

Talk given when receiving the award for the best exploratory research on behalf of the Institute of Environment and Sustainability.

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  • 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).
  • 4. Vela Laboratory Institute for Environment and Sustainability
  • 5. Experimental number distributions Institute for Environment and Sustainability 6 × 107 1.2 × 108 1.8 × 108 2.4 × 108 inlet outlet ● lognormal fit dN dlogdagg [cm−3] ●● ●●● ● ● ●● ● ●●● ● ● ●● ● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ● ●● ● ●● ●● ● ● ● ● ● ●● ● ● ●● ● ● ● ● ● ● ●● ●● ●● ● ● ●● ● ● ●● ● ● ●● ● ● ● ● ● ● ● ● ●● ● ● ● ● ● ● ● 0 ● 20 50 100 200 500 dagg [nm] • Lognormal number distribution (EURO3 vehicle, 120Km/h) (log dagg − log µ)2 N∞ dN fit = √ exp − d log dagg . 2 log2 σ 2π log σ • Compact way of representing the data: N∞ , µ and σ unambiguously describe the experimental data.
  • 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
  • 9. Aggregate Morphologies Institute for Environment and Sustainability
  • 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.