Ions in motor vehicle exhaust and their dispersion near busy roads

Measurements in the exhaust plume of a petrol-driven motor car showed that molecular cluster ions of both signs were present in approximately equal amounts. The emission rate increased sharply with engine speed while the charge symmetry remained unchanged. Measurements at the kerbside of nine motorways and five city roads showed that the mean total cluster ion concentration near city roads (603 cm-3) was about one-half of that near motorways (1211 cm-3) and about twice as high as that in the urban background (269 cm-3). Both positive and negative ion concentrations near a motorway showed a significant linear increase with traffic density (R2=0.3 at p<0.05) and correlated well with each other in real time (R2=0.87 at p<0.01). Heavy duty diesel vehicles comprised the main source of ions near busy roads. Measurements were conducted as a function of downwind distance from two motorways carrying around 120-150 vehicles per minute. Total traffic-related cluster ion concentrations decreased rapidly with distance, falling by one-half from the closest approach of 2m to 5m of the kerb. Measured concentrations decreased to background at about 15m from the kerb when the wind speed was 1.3 m s-1, this distance being greater at higher wind speed. The number and net charge concentrations of aerosol particles were also measured. Unlike particles that were carried downwind to distances of a few hundred metres, cluster ions emitted by motor vehicles were not present at more than a few tens of metres from the road

Application of bag sampling technique for particle size distribution measurements

Bag sampling techniques can be used to temporarily store an aerosol and therefore provide sufficient time to utilize sensitive but slow instrumental techniques for recording detailed particle size distributions. Laboratory based assessment of the method were conducted to examine size dependant deposition loss coefficients for aerosols held in VelostatTM bags conforming to a horizontal cylindrical geometry. Deposition losses of NaCl particles in the range of 10 nm to 160 nm were analysed in relation to the bag size, storage time, and sampling flow rate. Results of this study suggest that the bag sampling method is most useful for moderately short sampling periods of about 5 minutes

Reassessing the financial and social costs of public transport

This paper uses a previously developed spreadsheet cost model which simulates public transport modes operated on a 12km route to analyse the total costs of different passenger demand levels. The previous cost model was a very powerful tool to estimate the social and operator cost for different public transport technologies. However, as the model is strategic based, some assumptions are very basic and idealized and the demand was assumed to be exogenous (externally fixed). When the level of demand is high for the lower capacity public transport technologies, passengers may find the incoming vehicle full and therefore they have to wait more than one service interval. This paper applies queueing theory to investigate the probability of having to wait longer than the expected service headways which will affect the average passenger waiting time. The extra waiting time for each passenger is calculated and applied in the spreadsheet cost model. The speed-flow equation in the original spreadsheet model assumes the speed decreases according to the ratio of the current frequency and the lane capacity which is based on the safety headway without any passenger boarding. However, this may vary in different operating environments. Therefore, the speed equation is improved by moving from a linear equation to a piecewise equation that considers the features of different operating environments. To evaluate the differences after applying these equations, endogenous demand rather than exogenous demand will be investigated by using the elasticities for passenger waiting time and journey time

Differences in Airborne Particle and Gaseous Concentrations in Urban Air between Weekdays and Weekends

Airborne particle number concentrations and size distributions as well as CO and NOx concentrations monitored at a site within the central business district of Brisbane, Australia were correlated with the traffic flow rate on a nearby freeway with the aim of investigating differences between weekday and weekend pollutant characteristics. Observations over a 5-year monitoring period showed that the mean number particle concentration on weekdays was (8.8±0.1)×103 cm−3 and on weekends (5.9±0.2)×103 cm−3—a difference of 47%. The corresponding mean particle number median diameters during weekdays and weekends were 44.2±0.3 and 50.2±0.2 nm, respectively. The differences in mean particle number concentration and size between weekdays and weekends were found to be statistically significant at confidence levels of over 99%. During a 1-year period of observation, the mean traffic flow rate on the freeway was 14.2×104 and 9.6×104 vehicles per weekday and weekend day, respectively—a difference of 48%. The mean diurnal variations of the particle number and the gaseous concentrations closely followed the traffic flow rate on both weekdays and weekends (correlation coefficient of 0.86 for particles). The overall conclusion, as to the effect of traffic on concentration levels of pollutant concentration in the vicinity of a major road (about 100 m) carrying traffic of the order of 105 vehicles per day, is that about a 50% increase in traffic flow rate results in similar increases of CO and NOx concentrations and a higher increase of about 70% in particle number concentration

Theoretical limits of scaling-down internal combustion engines

Small-scale energy conversion devices are being developed for a variety of applications; these include propulsion units for micro aerial vehicles (MAV). The high specific energy of hydrocarbon and hydrogen fuels, as compared to other energy storing means, like batteries, elastic elements, flywheels and pneumatics, appears to be an important advantage, and favors the ICE as a candidate. In addition, the specific power (power per mass of unit) of the ICE seems to be much higher than that of other candidates. However, micro ICE engines are not simply smaller versions of full-size engines. Physical processes such as combustion and gas exchange, are performed in regimes different from those that occur in full-size engines. Consequently, engine design principles are different at a fundamental level and have to be re-considered before they are applied to micro-engines. When a spark-ignition (SI) cycle is considered, part of the energy that is released during combustion is used to heat up the mixture in the quenching volume, and therefore the flame-zone temperature is lower and in some cases can theoretically fall below the self-sustained combustion temperature. Flame quenching thus seems to limit the minimum dimensions of a SI engine. This limit becomes irrelevant when a homogeneous-charge compression-ignition (HCCI) cycle is considered. In this case friction losses and charge leakage through the cylinder-piston gap become dominant, constrain the engine size and impose minimum engine speed limits. In the present work a phenomenological model has been developed to consider the relevant processes inside the cylinder of a homogeneous-charge compression-ignition (HCCI) engine. An approximated analytical solution is proposed to yield the lower possible limits of scaling-down HCCI cycle engines. We present a simple algebraic equation that shows the inter-relationships between the pertinent parameters and constitutes the lower possible miniaturization limits of IC engines

Low-energy photoelectron transmission through aerosol overlayers

The transmission of low-energy (<1.8eV) photoelectrons through the shell of core-shell aerosol particles is studied for liquid squalane, squalene, and DEHS shells. The photoelectrons are exclusively formed in the core of the particles by two-photon ionization. The total photoelectron yield recorded as a function of shell thickness (1-80nm) shows a bi-exponential attenuation. For all substances, the damping parameter for shell thicknesses below 15nm lies between 8 and 9nm, and is tentatively assigned to the electron attenuation length at electron kinetic energies of ~0.5-1eV. The significantly larger damping parameters for thick shells (> 20nm) are presumably a consequence of distorted core-shell structures. A first comparison of aerosol and traditional thin film overlayer methods is provided

US 730 corridor refinement plan

168 pp. Tables, figures, appendices. Published October, 2007. Captured September 29, 2009.[T]he US 730 Corridor Refinement Plan was developed to identify circulation and access-management strategies that would address the corridor’s near- and long-term safety needs. [From the Plan

Developing Low Gasoline Particulate Emission Engines Through Improved Fuel Delivery

Particulate emissions are of growing concern due to health impacts. Many urban areas around the world currently have particulate matter levels exceeding the World Health Organisation safe limits. Gasoline engines, especially when equipped with direct injection systems, contribute to this pollution. In recognition of this fact European limits on particulate mass and number are being introduced. A number of ways to meet these new stringent limits have been under investigation. The focus of this paper is on particulate emissions reduction through improvements in fuel delivery. This investigation is part of the author's ongoing particulate research and development that includes optical engine spray and combustion visualisation, CFD method development, engine and vehicle testing with the aim to move particulate emission development upstream in the development process. As part of this work, a spark eroded and a laser drilled injector were fully characterised in a spray vessel under key engine running conditions. Injector nozzle geometries and mass flow data were also measured in great detail. This paper demonstrates using both steady state and transient engine testing that very significant improvements in particulate emissions can be made. Control strategies enabling multiple injections of smaller volumes of fuel per injection are the most promising technology. The MAHLE Flexible ECU (MFE) combined with injector testing allowed early stage development and demonstrated these effects for a number of key engine operating conditions. Most notably it was found that particulate matter emissions could be reduced by 80-90% during the catalyst light off phase. A new approach was developed (MASTER) to simultaneously assess the effects of calibration changes on all emissions to increase testing efficiency and hence get to more optimised solutions faster. This approach was successfully tested on a production engine comparing two injectors achieving 82% reduction in particulate number emissions during the first 200seconds of the NEDC relative to the EU5b baseline. Finally it was found that both fuel properties and injector deposits can have a significant effect on particulate emissions

Nanoparticle formation in the exhaust of vehicles running on ultra-low sulfur fuel

International audienceThe concern of adverse health impacts from exposure to vehicle-emitted nanoparticles has been escalating over the past few years. In order to meet more stringent EPA emission standards for particle mass emissions, advanced exhaust after-treatment systems such as continuously regenerating diesel particle filters (CRDPFs) have to be employed on vehicles and fuel with ultra-low sulfur is to be used. Although CRDPFs were found to be effective in reducing particle mass emissions, they were revealed to increase the potential of volatile nanoparticle formation. Significant nanoparticle concentrations have also been detected for vehicles running on ultra-low sulfur fuel but without CRDPFs. The main focus of this paper is the formation and evolution of nanoparticles in exhaust plume under ultra-low sulfur condition. Such study is necessary to project future nanoparticle emissions as fuel compositions and after-treatment systems change. We have carried out a comprehensive quantitative assessment of the effects of enhanced sulfur conversion efficiency, sulfur storage/release, and presence of non-volatile cores on nanoparticle formation using a detailed composition resolved aerosol microphysical model with a recently improved H2SO4-H2O homogeneous nucleation (BHN) module. Two well-controlled case studies show good agreement between model predictions and measurements in terms of particle size distribution and temperature dependence of particle formation rate, which leads us to conclude that BHN is the main source of nanoparticles for vehicles equipped with CRDPFs. We found that the employment of CRDPFs may lead to the higher number concentration of nanoparticles (but smaller size) in the exhaust of vehicles running on ultra-low sulfur fuel compared to those emitted from vehicles running on high sulfur fuel. We have also shown that the sulfate storage and release effect can lead to significant enhancement in nanoparticle production under favorable conditions. For vehicles running on ultra-low sulfur fuel but without CRDPFs, the BHN is negligible; however, the condensation of low volatile organic compounds on nanometer-sized non-volatile cores may explain the observed nucleation mode particles