On-Road Measurements of Spark Ignition Nanoparticle Emissions D. B. Kittelson University of Minnesota Department of Mechanical Engineering Minneapolis, MN 5 th ETH Conference on Nanoparticle Measurement Zurich 7 August 2001
Typical Diesel Particle Size Distributions, Number, Surface Area, and Mass Weightings Are Shown 0.25 Normalized Concentration, dc/c total /dlogdp 0.2 0.15 0.1 0.05 Nuclei Mode - Usually consists of particles formed from volatile precursors as exhaust mixes with air during dilution Nanoparticles Dp < 50 nm Ultrafine Particles Dp < 100 nm Fine Particles Dp < 2.5 µm PM10 Dp < 10 µm Accumulation Mode - Usually consists mainly of carbonaceous agglomerates that have survived the combustion process Coarse Mode - Usually consists of re-entrained particles, crankcase fumes 0 0.001 0.010 0.100 1.000 10.000 Diameter (µm) Mass Weighting Number Weighting Surface Weighting
Nanoparticle Formation: Current working hypothesis - based mainly on Diesel studies Most of the particles are formed from volatile precursors by nucleation and growth as the exhaust dilutes and cools in the atmosphere Nanoparticles are volatile and easily removed by heating The formation of nanoparticles is very, very dependent on dilution conditions Heavy hydrocarbons (lube oil) and sulfuric acid are primary constituents of nanoparticles ash may play an important role for some engines Low levels of soot in the exhaust compared to volatile precursors make volatile nanoparticle formation more likely at least under some lab conditions
Particles from Spark Ignition Engines - Approximate Composition of Exhaust Particulate Matter Well Maintained Port Fuel Injection Engines 10% 5% 5% Unresolved complex mixture (UCM)* Ash Sulfates, carbon, etc. 80% Oxygenated and PAC * Includes branched and cyclic compounds Based on Ricardo data
Particle Emissions from Port Fuel Injection (PFI) Spark Ignition Engines PFI engine exhaust particles are quite different from diesel particles They usually smaller They are composed primarily of volatile materials Formation likely to be associated by local inhomogeneous conditions - big droplets, crevices Lube oil may play an important role especially in worn engines» Volatile material» Ash PFI emissions are strongly influenced by dilution and sampling conditions, and past history They are formed from volatile precursors during dilution Storage and release of precursors from exhaust system may be involved Sulfuric acid-water nucleation and hydrocarbon absorption and, possibly, direct nucleation of heavy hydrocarbon derivatives
U of M Mobile Laboratory built to study formation of nanoparticles in the atmosphere for the CRC E-43 project
Principal Instruments in MEL SMPS to size particles in 9 to 300 nm size range ELPI to size particles in 30 to 2500 nm size range CPC to count all particles larger than 3 nm Diffusion Charger to measure total submicron particle surface area Epiphaniometer to measure total submicron particle surface area PAS to measure total submicron surface bound PAH equivalent CO 2, CO, and NO analyzers for gas and dilution ratio determinations
MNDOT Study Goals and Objectives Determine the relationship between traffic congestion and nanoparticle concentrations over highways. Estimate fuel specific emissions factors for our current vehicle fleet. Determine the concentrations of nanoparticles in neighborhoods near major highways.
Nanoparticles exist over Minnesota highways both with and without significant Diesel traffic 300000 dn/dlogdp (Particles/cm 3 ) 250000 200000 150000 100000 No diesels 39 scans Diesels 30 scans Measurements made at passenger car air inlet level moving with traffic 50000 0 1 10 100 1000 Mid-point diameter, nm
Size Distributions, 1993 GM 2.3L Quad-4, 3500 RPM, 100 kpa MAP, Single Stage Ejector Diluter 1.4E+08 1.2E+08 dn/dlogd p (particles/cm 3) 1.0E+08 8.0E+07 6.0E+07 4.0E+07 DR = 10.9 DR = 11.7 DR = 15.3 DR = 20.5 DR = 25.4 2.0E+07 0.0E+00 1 10 100 1000 Particle Diameter, D p (nm)
More nanoparticles are present in fast moving traffic than in traffic jams 900000 dn/dlogdp (Particles/cm 3 ) 800000 700000 600000 500000 400000 300000 200000 100000 55 mph average 10 scans Traffic jam average 30 scans I-94 and I-694 I-494 0 1 10 100 1000 Mid-point diameter, nm
Measurements upwind and downwind of Interstate 494 particles persist downwind dn/dlogdp (Particles/cm 3 ) 20000 15000 10000 5000 Upwind - Continuous Upwind - Bag Downwind - Continuous Downwind - Bag 42nd Place W of Northwest Blvd Fernbrooke and 42nd Ave 0 1 10 100 1000 Avg 4 continuous and 3 bags each location Mid-point diameter, nm
Fuel specific emissions may be calculated by comparing onroad and background these measurements made at low ambient temperature, ~ 5 C We determine fuel specific number and mass emissions, EI N (particles/kg fuel ) and EI m (mass/kg fuel ) from: N EI N = x + x M / M y ρ EI m = ( CO CO )( C air ) C air 2 (all values corrected for background) These values mass be converted to particles/mile or mass/mile if fuel consumption is known (assume 20 MPG) using: particles / mile = EI /( ρ MPG) m fuel ( xco + xco )( M C / M air ) yc ρair 2 N fuel fuel On road number and mass emission factors EI N CPC (particles/g fuel ) 2 11 x 10 12 EI N SMPS (particles/g fuel ) 1 3 x 10 12 EI m SMPS (µg/g fuel ) 70 330 Particles/mile CPC 3 14 x 10 14 Particles/mile SMPS 1 4 x 10 14 mg/mile SMPS 10-19
Recent European measurements show gasoline off cycle, gasoline direct injection and Diesel in same number emission range (Färnlund et al., 2001)
Conclusions spark ignition engine nanoparticles Both Diesel and spark ignition engines have significant onroad nanoparticle emissions The size distributions for spark ignition engines exhibit relatively large nuclei modes and small accumulation modes (low mass emissions) compared to Diesel engines Similar size distributions have been observed in the laboratory and on-road More spark ignition particles are present in faster moving traffic and as fleet accelerates storage and release effect On-road fuel specific number emissions at high end of lab measurements reported in the literature. These measurements were made at low ambient temperatures (~ 5 C) likely to increase nanoparticle formation more work must be done.