Nuclei Mode Particles Research Articles

Feasibility of Measuring Brake-Wear Particle Emissions from a Regenerative-Friction Brake Coordination System via Dynamometer Testing

Emissions of brake-wear particles are commonly associated with vehicular traffic. We investigated the feasibility of quantifying brake-wear particle emissions under realistic vehicle driving and braking conditions with a currently used regenerative friction brake coordination system. We used a braking system installed in commercially available plug-in hybrid electric vehicles and found that it reduced emissions by 85% for PM10, 78% for PM2.5, and 87% for particle numbers (PNs) compared with the system installed in vehicles with internal combustion engines. Brake friction work showed a linear relationship with PM10 and PM2.5. Nanoparticle PM emissions tended to increase slightly with regenerative braking but did not contribute significantly to the overall PM percentage. The emission events of high concentrations of nuclei-mode particles (<20 nm in diameter) in electric vehicle brake assemblies designed for regenerative braking use under high-temperature, high-load braking conditions with full-friction brakes. The nuclei-mode particles amplified the PN emissions and led to high variability. In strict regulatory certification tests where measurement reproducibility and stability are required, it is appropriate to measure PNs under brake conditions appropriate for the actual use of electric vehicles rather than under full-friction brake conditions or to remove particle measurements smaller than 20 nm.

Fuel property impacts on gaseous and PM emissions from a multi-mode single-cylinder engine

The U.S. Department of Energy’s Co-Optima initiative has focused on improving fuel economy and vehicle performance while reducing emissions through the simultaneous development of emerging sustainable fuels with beneficial properties and advanced combustion strategies. A major thrust has been the development of advanced compression ignition (ACI) combustion strategies of gasoline range fuels in combination with spark-ignited (SI) combustion in a single engine capable of multi-mode operation to achieve high power density with enhanced part load efficiency. The aim of this study was to further the understanding of how emissions from both ACI and SI strategies operating on the same fuels in the same engine are impacted by different fuel properties. This investigation focused on particulate matter (PM) and gaseous hydrocarbon emissions from 6 different fuels across 3 different combustion modes on the same single-cylinder engine designed for multi-mode operation: SI combustion, partial fuel stratification (PFS), and spark-assisted compression ignition (SACI). In each of these modes, 3 different CA50 phasings were studied such that all 6 fuels could be studied at the same phasings. Three of the six different fuels used were specially formulated in a previous investigation to study the impact of fuel distillation and aromatic content while maintaining the research octane number (RON) and octane sensitivity. Additionally, neat isooctane and two ethanol containing fuels (RD5-87 and Co-Optima E30) were studied. Different fuel and phasing impacts on emissions were observed across the three combustion modes. Fuel properties were found to impact soot PM and particle number more than the CA50 phasing, while the phasing had more impact on NOx emissions. The NOx emissions were reduced in the PFS mode for all fuels compared to SI combustion, but the SACI combustion mode did not reduce NOx emissions. Although PFS produced low soot PM emissions like SI, total PM mass emissions were significantly higher due to large organic carbon (OC) PM mass contribution. Both PFS and SACI had greater particle number emission than SI operation with small nuclei mode particles dominating in PFS compared to large agglomeration particles in SACI.

Particle emissions of a heavy-duty engine fueled with polyoxymethylene dimethyl ethers (OME)

OME as sustainable alternative diesel fuel burns without the agglomeration of soot particles which is the case for fossil and paraffinic diesel fuels. Nuclei mode particles are mainly of a volatile nature and do not survive exhaust aftertreatment.

Experimental and numerical investigations into effects of urea-water solution injection on tailpipe particulate matter emissions

Selective catalytic reduction (SCR) is currently the most effective method to control NOx emissions for heavy-duty vehicles. However, urea-water solution injection may lead to increase of particulate matter (PM) emissions. In this study, PM emissions caused by urea-water solution injection from a China VI heavy-duty vehicle under real-world driving conditions is investigated experimentally. Average PM number emissions increase by over 200 % due to urea-water solution injection. Inlet temperature and space velocity are found to be significant factors. Droplet depletion model is developed for analyzing the contribution of urea decomposition by-products. Results suggest that secondary-breakup-based particles is major contributor to particles formation instead of primary-breakup-based. About 20 % of secondary-breakup-based particles are nuclei mode particles and 80 % are accumulation mode particles. The main component of the secondary-breakup-based particles is cyanuric acid and ammelide.

Particle Size Distribution of PM Emission from In-use Gasoline and Diesel Vehicles

Particle size distribution and emission factors from 9 State 3-5 light-duty gasoline vehicles (LDGVs) and 15 State 3-5 heavy-duty diesel vehicles (HDDVs) were tested in this study using a constant volume sampling (CVS) system on a dynamometer. The influences of driving cycles and emission control level on the PM emission factors and particle size distribution were analyzed. The results show that the PM emission factors of the tested LDGVs and HDDVs were (4.1±4.0)×1014 and (5.7±4.3)×1015 kg-1, respectively; the HDDV PM emission factor was (14±7) times less than that of LDGVs. Regarding LDGVs, the PM emission factor under the extra high speed condition was much more than that of the other speed conditions at (5.1±5.0)×1013 km-1, 11.7, 14.1, and 7.3 times more than that under the low, medium, and high speed conditions, respectively. Regarding HDDVs, the emission factor under the high speed condition was 2.5 and 1.4 times that under the low and medium speed conditions, respectively, and was mostly of nuclei-mode particles. At the emission control level of State 3-5, the PM emission factors of LDGVs were (2.7±1.7)×1013, (2.6±1.3)×1013, and (1.6±1.2)×1013 km-1, respectively, and those of HDDVs were (2.2±1.2)×1015, 2.0×1015, and (7.1±2.1)×1014 km-1, respectively. With improvement in emission control level, the particle number emission control of LDGVs and HDDVs generally showed a good downward trend. However, the emission of PM above 110 nm from LDGVs did not improve with the emission control level. Although the quantity emission factor of HDDVs with particle size above 110 nm is relatively low, its harm to the environment cannot be ignored, which should justify necessary attention.

Primary emissions and secondary organic aerosol formation from in-use diesel vehicle exhaust: Comparison between idling and cruise mode

Diesel vehicle exhaust is an important source of carbonaceous aerosols, especially in developing countries, like China. Driving condition impacts diesel vehicle emissions, yet its influence needs further understanding especially on secondary organic aerosol (SOA) formation. In this study tailpipe exhaust from an in-use light duty diesel vehicle at idling and driving speeds of 20 and 40 km h−1 was introduced respectively into a 30 m−3 indoor smog chamber to investigate primary emissions and SOA formation during photo-oxidation. The emission factors of SO2 at 20 and 40 km h−1 were higher than those at idling, whereas the emission factors of aromatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs) and oxygenated volatile organic compounds (OVOCs) decreased when driving speeds increased. The emission factors of black carbon (BC) and primary organic aerosol (POA) at idling were comparable to those at 20 and 40 km h−1. The SOA production factors were 0.41 ± 0.09 g kg-fuel−1 at idling, approximately 2.5 times as high as those at 20 km h−1 (0.16 ± 0.09 g kg-fuel−1) or 40 km h−1 (0.17 ± 0.09 g kg-fuel−1). Total carbonaceous aerosols, including BC, POA and SOA, from diesel vehicles at 20 and 40 km h−1 were 60–75% of those at idling, due largely to a reduction in SOA production. Measured AHs and PAHs altogether were estimated to explain <10% of SOA production, and eight major OVOCs could contribute 8.4–23% of SOA production. A preliminary comparison was further made for the same diesel vehicle at idling using diesel oils upgraded from China 3 to China 5 standard. The emission factors of total particle numbers decreased by 38% owing to less nuclei mode particles, which was probably caused by the reducing fuel sulfur content; the emission factors of BC were almost unchanged, the POA emission factors and SOA production factors however decreased by 72% and 37%.

10-Month characterization of the aerosol number size distribution and related air quality and meteorology at the Bondville, IL Midwestern background site

The aerosol size distribution was measured at a rural continental U.S. location (Bondville, Illinois 40.05∘N and 88.37∘W) for the period July 2013–June 2014. The dehumidified size distribution in the range 3 nm to 2.5 μm was continuously recorded by two scanning mobility particle sizers and an aerodynamic particle sizer. The Illinois measurement site is significant because it is home to one of the longest records (20+ years) in North America of atmospheric aerosol, meteorology, and gas phase variables. It is a common site for model-measurement comparison of both chemical and aerosol microphysical variables. However, while the measurement record has aerosol number concentration and optical properties, the number size distribution has not been well-constrained. Measurement highlights include means in number concentration (3–2500 nm), aerosol optical depth, SO2, NH3, and PM2.5 of 6500 cm−3, 0.18, 0.87 ppb, 1.6 ppb, and 8.8 μg m−3, respectively. The mode in the mean size distribution was 31 nm (number) and 287 nm (volume). The mean size distribution was heavily influenced by nuclei mode particles, with 46% of particles smaller than 20 nm. New particle formation and growth events increase midday concentrations of 3–50 nm particles substantially, with the highest activity in spring months and lower activity in summer and winter. Short term elevations in particle number and mass associated with local agricultural burning in April are reported as well.

Physico-chemical speciation of particulates emanating from Karanja biodiesel fuelled automotive engine

It is essential to reduce emissions from the existing vehicles, in order to preserve the environment. In this study, Karanja oil derived biodiesel generated particulates emanating from a medium-duty transportation diesel engine fitted with a diesel oxidation catalyst (DOC) were characterised. Regulated gaseous emissions, particle size–number distributions, elemental carbon (EC) and organic carbon (OC) of these particulates were determined under varying engine load conditions (no load, 25%, 50%, 75% and 100% load at rated torque speed of 2500rpm) in order to assess the effectiveness of biodiesel blend (B20) compared to mineral diesel in combination with the use of DOC. Particle size–number distribution showed significantly higher concentration of nuclei mode particles for both test fuels. Particle size–number distribution was observed to be bimodal in nature and in two size ranges: less than 10nm and 25–250nm, respectively. This study reports few important insights into possible use of biodiesel in effectively reducing overall particulate emissions as well as gaseous emissions from automotive diesel engines fitted with DOC.

Evaluation on toxic reduction and fuel economy of a gasoline direct injection- (GDI-) powered passenger car fueled with methanol–gasoline blends with various substitution ratios

Methanol exhibits better capability of lowering engine emissions and fuel cost, but a potential rise in pipe-out NOx and carbonyl emissions has increased health-related risks and stalled its application. This paper examined regulated, unregulated and particulate emissions from a 1.8L GDI-powered passenger car running the New European Driving Cycle (NEDC). Conventional gasoline, together with three gasohol samples with 15%, 25% and 40% methanol substitution (M15, M25 and M40), was used. To evaluate health risk linked with pipe-out formaldehyde and benzene, a human exposure model was established. The results showed that compared with gasoline, burning gasohol significantly reduced pipe-out CO and HC emissions. Evident decrease in NOx emission was noticed with M15 and M25 fueling, but in the case of M40, NOx emissions were similar with gasoline. Carbonyls, about 50% of which were found formaldehyde, surged sharply with increased methanol percentage in the blend, while VOCs showed an opposite propensity. Health risk assessment showed that, even under a severe exposure condition, the levels of exhaust-borne formaldehyde and benzene were not sufficient to cause acute or chronic symptoms. Cancer-related risks induced by gasoline and gasohol engine exhaust were found in the same magnitude. Burning gasohol enabled an over 30% PM removal but resulted in an increase in particulate number due to an increased number of nuclei-mode particles. At last, burning gasohol produced about 0.8–4.1% less pipe-out CO2 emission than gasoline, while saving fuel cost by 5.7–15%.

Factors Affecting the Ambient Physicochemical Properties of Cerium-Containing Particles Generated by Nanoparticle Diesel Fuel Additive Use

Despite the use of cerium oxide nanoparticles (nCe) in some regions as a diesel fuel additive, the physicochemical properties of the resulting exhaust particles in the ambient atmosphere are not well known. The mixing state of ceria with other exhaust particles is one such physicochemical property that has been shown to potentially affect ecosystem/human health. In this study, cerium-containing particles associated with an nCe additive were collected in the laboratory and in Newcastle-upon-Tyne, UK where the local bus fleet uses the Envirox nCe additive. Electron microscopy of laboratory-generated exhaust samples indicated both individual ceria and soot particles (external mixture) and ceria contained within soot agglomerations (internal mixture). Low ambient concentrations prevented quantification of the ceria particle mixing state in the atmosphere; therefore, a multicomponent sectional aerosol dynamic model was used to predict the size, chemical composition, and mixing state of ceria particles as a function of distance from an idealized roadway. Model simulations predicted that most ceria particles remain nonmixed in the ambient atmosphere (300 m downwind from the roadway) due to slow coagulation, with the mixing rate most sensitive to the ceria content of emitted nuclei-mode particles and the particle concentration upwind of the road. Although microscopy analysis showed both external and internal mixtures of ceria and soot in freshly emitted particles, the ambient mass concentration, and size distribution of ceria particles predicted by the model was insensitive to the emitted mixing state.Copyright 2015 American Association for Aerosol Research

Influence of an iron-based fuel-borne catalyst on physicochemical and toxicological characteristics of particulate emissions from a diesel engine

Metal-based fuel-borne catalysts (FBCs) have been used with diesel fuels to effectively reduce soot and diesel particulate matter (DPM) emissions from both on-road and off-road applications. However, there is a lack of detailed investigations on the potential changes in the properties of particulates, when FBCs-doped fuels are combusted in diesel engines. This study fully evaluates the potential impacts of ferrocene-doped ultralow sulfur diesel (ULSD) fuels on physical, chemical and toxicological characteristics of the particulates emitted by a single cylinder, direct-injection diesel engine working at a constant speed and at three engine loads. The results indicated that ferrocene-doped fuels could effectively reduce the particulate mass and elemental carbon (EC) emissions, while increasing the proportion of both organic carbon (OC) and water-soluble organic carbon (WSOC) in particles. Particle-phase PAHs and n-alkanes emissions increased with an increase of Fe in the fuels. Ferrocene addition also led to lower soot ignition temperature and activation energy. However, the total number emissions of particles from ferrocene-doped fuels dramatically increased due to the formation of Fe-rich nuclei mode particles. Compared to pure ULSD, the particles emitted from ferrocene-doped fuels showed a slight decline in cell viability. The Fe in the particles and the changes in chemical composition of particulates are thought to be responsible for the variation of cell viability.

Characteristics of new particle formation events in Nanjing, China: Effect of water-soluble ions

New particle formation (NPF) events and water-soluble ions were studied at the meteorological building on the campus of the Nanjing University of Information Science and Technology (NUIST), which is located in the western part of the Yangtze River Delta (YRD). A wide-range particle spectrometer (WPS) provided particle number size distributions between 10 nm and 10 μm, whereas water-soluble ions for particles with diameters between 10 nm and 18 μm were measured using a 13-stage Nano-MOUDI aerosol sampler and 850 professional Ion Chromatography (IC). Additionally, meteorological data, trace gas concentrations and mass concentration were recorded. Ten NPF days were captured during the measurement period from 08 July to 02 August 2012. The mean aerosol number concentration, which was primarily composed of Aitken-mode particles, i.e., with diameters of 20–100 nm, was 13,664 cm−3, which was 1.9 times larger than that on non-NPF days. The results suggest that the NPF events were only slightly affected by O3, SO2, and NO2; the primary factors affecting NPF events were meteorological factors and air mass directions. NPF events were found to be favorable during the summer in the presence of high temperatures, strong radiation, low humidity, strong winds and clean air masses originating from the southeastern coast. The mean growth rate (GR), formation rate (J10), condensational sink (CS), condensing vapor rate (Q), and condensation vapor (C) were determined to be 7.6 nm h−1, 3.7 cm−3 s−1, 2.8 × 10−2 s−1, 2.9 × 106 cm−3 s−1, and 10.5 × 107 cm−3, respectively, on NPF days. The largest effects of the studied NPF events were on the mass and water-soluble ion concentrations of Aitken-mode particles, followed by nuclei-mode particles; few contributions to accumulation- and coarse-mode particles were observed. Different water-soluble ions were observed to have distinct interactions with the NPF events. The proportions of NH4+, SO42−, NO3−, K+ and Mg2+ in nuclei- and Aitken-mode particles to the total concentrations on NPF days were substantially higher than on non-NPF days.

Crankcase gaseous and particle emissions in common rail diesel engine

In this study, the crankcase gas temperature, flow rate, gaseous emissions (NOx, CO and HC) and particle emissions (particle size distribution, number and mass concentration, geometric mean diameter) compared with tailpipe are investigated in a light-duty common rail diesel engine. It is shown that the emissions from the crankcase are mainly affected by the second in-cylinder pressure peak. The crankcase gas temperature varies between 52 °C and 68 °C, and the crankcase gas flow rate slightly increases with load and speed but does not vary much with injection timing. The CO emission from crankcase is about 2%−5% of that from tailpipe, the NOx emissions are only about 1% and the HC emissions are more than 10%. The blow-by gas percentage is 10−8 order and reduces with heavier engine load and faster engine speed. The blow-by HC emission percentage varies from 5% to 35%. As engine load is increased and engine speed is decreased, the nuclei mode particles of crankcase reduce and the accumulation mode particles increase. Furthermore, the particle total number concentration increases with load but decreases with speed and retarding injection timing. The total mass concentration increases with load but rises and falls with speed and injection timing. The crankcase particle geometric mean diameter based on mass is nearly twice larger than that of tailpipe, while the ones based on number are rarely different except the higher load.

Near-road modeling and measurement of cerium-containing particles generated by nanoparticle diesel fuel additive use.

Cerium oxide nanoparticles (nCe) are used as a fuel-borne catalyst in diesel engines to reduce particulate emissions, yet the environmental and human health impacts of the exhaust particles are not well understood. To bridge the gap between emission measurements and ambient impacts, size-resolved measurements of particle composition and mass concentration have been performed in Newcastle-upon-Tyne, United Kingdom, where buses have used an nCe additive since 2005. These observations show that the noncrustal cerium fraction thought to be associated with the use of nCe has a mass concentration ∼ 0.3 ng m(-3) with a size distribution peaking at 100-320 nm in aerodynamic diameter. Simulations with a near-roadway multicomponent sectional aerosol dynamic model predict that the use of nCe additives increases the number concentration of nuclei mode particles (<50 nm in diameter) while decreasing the total mass concentration. The near-road model predicts a downwind mass size distribution of cerium-containing particles peaking at 150 nm in aerodynamic diameter, a value similar to that measured for noncrustal cerium in Newcastle. This work shows that both the emission and atmospheric transformation of cerium-containing particles needs to be taken into account by regional modelers, exposure scientists, and policymakers when determining potential environmental and human health impacts.

On-road measurement of regulated pollutants from diesel and CNG buses with urea selective catalytic reduction systems

In this study, emissions from 13 buses operated in Beijing, including two Euro-III diesel buses, four Euro-IV diesel buses, three Euro-V diesel buses and four Euro-V CNG buses, were characterized in real world conditions. All of the buses tested were fitted with selective catalytic reduction (SCR) systems except for the Euro-III diesel buses. A SEMTECH-DS was used for testing the gaseous pollutants, and an electric low pressure impactor (ELPI) was used for measuring of particle numbers and size distributions. A comparison was made based on emission performance of these buses by employing the VSP approach and fuel- based emissions factors. Diesel buses emitted less CO and THC but more NOx and PM pollutants than CNG buses. The NOx reduction efficiencies of the SCR systems for CNG buses were higher because of the high exhaust temperature and high NO2/NOx ratio, whereas the efficiencies for diesel buses were lower. This resulted in extremely low NOx emissions from CNG buses, but the high NO2/NOx ratio needs further study. Failures of urea injection in the SCR systems were detected in this research, which resulted in very high NOx emissions. The CNG buses also emitted smaller numbers of particles and less particle mass with the presence of oxidation catalysts. Diesel buses satisfying the Euro-V standard performed better than Euro-IV and Euro-III diesel buses in terms of emission performance, except for more nuclei mode particles. Most of time, the Euro-IV diesel buses show no advantages in CO and NOx emissions compared with the Euro-III diesel buses.

The influence of electric charge on minimum particle scavenging efficiency particle size during below-cloud scavenging processes

Below-cloud wet deposition scavenging processes are important for removing coarse and very fine particles from the atmosphere. This study investigated the influence of electric charge on particle deposition and estimated the scavenging gap particle size (the most penetrating particle size) along with the corresponding minimum collection efficiency and minimum scavenging coefficient particle size by using equations for below-cloud scavenging processes. A harmonic mean type approximation was used for calculations and the Cunningham correction factor was applied to include the slip effect of nuclei mode particles. Results based on the analytically approximated solution compared well with the numerically calculated results and previous studies that did not consider electric charging effects. The results showed that charge effects play an important role in determining the most penetrating particle size. This study also showed that use of the Cunningham correction factor may increase the most penetrating particle size under certain conditions. Subsequently, these results indicate that consideration of the electric charge effect with a Cunningham correction factor is important for estimating the most penetrating particle size.

Effect of biodiesel on particulate numbers and composition emitted from turbocharged diesel engine

In present study a turbocharged, medium duty compression ignition engine was alternatively fuelled with biodiesel to investigate the changes in particulate matter composition, relative to that taken with diesel fuel. The engine was operated on an AC electrical dynamometer in accordance with an 8-mode, steady-state cycle. The numbers of particles were estimated through electrical low pressure impactor, while sulfates and trace metals were analyzed by ion chromatography and inductively coupled plasma-atomic emission spectroscopy, respectively. Nitric oxides and nitrogen dioxides were measured separately using SEMTECH-DS. Experimental results revealed that, on account of elevated ratios of nitrogen dioxide to nitrogen oxides, mean accumulation mode particles were 42 % lower with biodiesel. On the other hand, nuclei mode particles were higher with biodiesel, owing to heterogeneous nucleation and accounting for an increase in sulfate emissions up to 8 % with biodiesel as compared to diesel. On the average, trace metal emissions were significantly reduced showing 65–85.4 % reduction rates with biodiesel, relative to its counterpart. Further to this, individual congeners such as iron, calcium, and sodium were the predominant elements of the trace metals emitted from engine. The mean relative decrease in iron and calcium was 89–97.8 and 77.6–87 %, respectively, while the relative rise in sodium was in the range of 29–46 % with biodiesel. Further, elements such as zinc, chromium, and aluminum showed substantial abatement, whereas potassium, magnesium, and manganese exhibited irregular trends on account of variable engine loads and speeds during the various modes of cycle.

Organic-rich nanoparticles (diameter: 10–30 nm) in diesel exhaust: Fuel and oil contribution based on chemical composition

Abstract The size distribution of particle number concentrations and comprehensive chemical composition (elemental and organic carbon, elements, ions, and organic compounds) by particle size (diameter: 0.010–10 μm) were measured under no-load and transient conditions in the exhaust from an 8-L diesel engine with no exhaust after-treatment system and from a 3-L diesel vehicle equipped with an oxidation catalyst. High concentrations of nuclei-mode particles were emitted from the 8-L engine under no-load condition (8L-NoLoad), even when low-sulfur (8 ppm) fuel was used, but no nuclei-mode particles were emitted from the 3-L vehicle. Organic carbon accounted for a major part (79–80%) of the measured components of the nanoparticles (diameter: 10–32 nm) under 8L-NoLoad, but elemental carbon accounted for only 8–15%; elements and ions including sulfate accounted for only small percentages. The mass chromatogram (m/z 85) patterns obtained by gas chromatography–mass spectrometry of the nanoparticles were similar to those for lubricating oil, and the peak profiles for hopanes were equivalent to those in oil. The 17α(H),21β(H)-hopane concentrations per particle mass were higher in smaller particles. The elements concentrated in oil were also concentrated in the nanoparticles. These results suggest that not sulfate and fuel but organics derived from oil were the primary components of the nanoparticles under 8L-NoLoad. From the 17α(H),21β(H)-hopane concentrations, the oil contribution to the sum of measured components in the nanoparticles under 8L-NoLoad was estimated at 79–92%. Comparable oil contributions were estimated from Ca and Zn concentrations.

Effects of continuously regenerating diesel particulate filters on regulated emissions and number-size distribution of particles emitted from a diesel engine

Abstract The effects of continuously regenerating diesel particulate filter (CRDPF) systems on regulated gaseous emissions, and number-size distribution and mass of particles emanated from a diesel engine have been investigated in this study. Two CRDPF units (CRDPF-1 and CRDPF-2) with different specifications were separately retrofitted to the engine running with European steady-state cycle (ESC). An electrical low pressure impactor (ELPI) was used for particle number-size distribution measurement and mass estimation. The conversion/reduction rate ( R CR) of hydrocarbons (HC) and carbon monoxide (CO) across CRDPF-1 was 83% and 96.3%, respectively. Similarly, the R CR of HC and CO and across CRDPF-2 was 91.8% and 99.1%, respectively. The number concentration of particles and their concentration peaks; nuclei mode, accumulation mode and total particles; and particle mass were highly reduced with the CRDPF units. The nuclei mode particles at downstream of CRDPF-1 and CRDPF-2 decreased by 99.9% to 100% and 97.8% to 99.8% respectively; and the particle mass reduced by 73% to 92.2% and 35.3% to 72.4%, respectively, depending on the engine conditions. In addition, nuclei mode particles increased with the increasing of engine speed due to the heterogeneous nucleation initiated by the higher exhaust temperature, while accumulation mode particles were higher at higher loads due to the decrease in the air-to-fuel ratio (A/F) at higher loads.

An Evaluation of Particle Size Distributions and Particle Number-Based Reductions from Various PM Emission Control Technologies

An Evaluation of Particle Size Distributions and Particle Number-Based Reductions from Various PM Emission Control Technologies