Particle Number Emissions Research Articles

Experimental Investigation on OBD Signal and PN Emission Characteristics by Damaged-DPF Types of 2.0 L Diesel Vehicle

A diesel particulate filter (DPF) is an exhaust after-treatment device designed to capture and store exhaust particulate matter, such as soot and ash, to reduce emissions from diesel-powered vehicles. A DPF has a finite capacity and typically uses a substrate made of ceramic material that is formed into a honeycomb structure. Diesel particulate filters play an important role in diesel-fueled vehicles. Failure to maintain these filters can have significant consequences for vehicles. In this study, we investigated the failure type in cordierite DPF substrates. In addition, we experimentally characterized the particle number (PN) emission and on-board diagnostics (OBD) signal of a 2.0 L diesel-fueled vehicle generated by three types of DPF failure (crack, melting, and hollow). Specifically, X-ray photography analysis of the cordierite DPF was performed. The PN and OBD signals were assessed via the KD-147 vehicle driving mode and measured using a DMS-500 (PN measurement device) and global diagnosis tool (GDS) scanner (OBD diagnostic device), respectively. X-ray photography was used to characterize the internal structure of the three DPF-failure samples. A key result was that the maximum value of the OBD data, including airflow mass, boost pressure, and VGT actuator, was distinctly different for each DPF sample. The exhaust temperature gradient for the normal DPF and crack-damaged DPF followed the KD-147 driving pattern. This was because there was no volume damage inside the cordierite DPF substrates. However, in the case of the hollow and melting-damaged DPF, the volume inside the cordierite DPF substrates was reduced or the time for the exhaust gas to stay in the DPF substrates was decreased. The melting-damaged DPF continuously emitted the largest number of nanoparticles (of the order of 109 #/cc). This was regardless of the vehicle driving speed in the KD-147 driving mode. Eventually, an OBD-based algorithm to determine whether a DPF is damaged was derived in this study.

Sub-23 particle control strategies towards Euro VII HD SI natural gas engines

Approaching Euro VII regulation limits for natural gas engines represents an arduous but not impossible challenge.The technological improvement and research progress in propulsion systems can offer strong tools in the achievement of next emission target. The efforts in this field are justified by the interests in natural gas powertrains that represent an alternative solution mainly in case of Heavy-Duty engines for off-road and transport applications. One of the aspects involving the OEMs effort is the particle number emissions abatement, that, due to the next future stringent limits involving sub-23 nm particles, represents a challenge also in case of natural gas fueled engines.The present paper describes the potentiality offered by different strategies in the control of particles emitted by Heavy-Duty natural gas engines. Three approaches will be described and analyzed using experimental characterization carried out by the authors with the use of an engine test bench. Assuming that the major source of particles derives from the lube oil combustion, firstly the effect of improved piston ring pack design has been assessed, comparing two versions of the same engine.Secondly the quality of lubricant oils in particle formation has been evaluated, testing oils with improved chemical/physical properties.A last aspect analyzed was the evaluation of the particulate filter technology capability when applied to a natural gas engine, a novelty in the scientific literature.All the investigated approaches proofed powerful tools in the control of sub-23 particle, paving the way for natural gas engines compliant with Euro VII PN limits.

Evaluating the filtration efficiency of close-coupled catalyzed gasoline particulate filter (cGPF) over the WLTC and simulated RDE cycles.

Gasoline particulate filter (GPF) is a cost-effective solution to particle number emissions from gasoline direct injection vehicles. Filtration efficiency, as a key parameter of GPF, was usually assessed at chassis level over regulatory drive cycles. However, the promulgation of real driving emission (RDE) requirements in the EU and Chinese regulations necessitates evaluations based on non-legislative cycles to guarantee the on-road emissions are compliant to regulatory requirements. In this research, two aggressive drive cycles, RTS95 at 23degC and modified RDE at 0degC, were complemented to the WLTC to evaluate the filtration efficiency of a catalyzed GPF (cGPF) in fresh conditions to obtain the so-called "worst-case" filtration efficiency. In the WLTC, RTS95, and simulated RDE tests, the filtration efficiency of the test cGPF was 51.1%, 41.3%, and 85.1% respectively. In the simulated RDE test, the test cGPF filtrated solid particles with a diameter above 23nm and 10nm at a similar efficiency. Increased filtration efficiency with heavier soot load could offset the relatively low filtration efficiency in cold-start and warm-up durations, hence the filtration efficiency for a clean cGPF showed higher sensitivity to cycle length over driving dynamics and testing temperature. In acceleration events with cGPF mounted, the particle diameter where number concentration peaked decreased as the engine warmed up. In deceleration events, bimodal and trimodal particle number size distributions with much lower concentrations were observed.

Sub-23 nm Particle Emissions from China-6 GDI Vehicle: Impacts of Drive Cycle and Ambient Temperature

Both the EU and China are evaluating the feasibility of lowering the detection limit of particle number (PN) measurement to 10 nm in future legislations, making it necessary to better understand the sub-23 nm particle emission characteristics from state-of-the-art vehicles. In this study, solid PN emissions with a diameter larger than 10 nm and 23 nm (known as SPN10 and SPN23) were compared over the WLTC, RTS95, and a so-called “worst-case” real driving emission (RDE) cycle (highly dynamic/0 °C) using two certification-level particle number counters (PNCs) employing evaporation tube (ET) and catalytic stripper (CS) as volatile particle remover (VPR). The results show that SPN10 emissions were 31.7%, 27.8%, and 15.2% higher than SPN23 over the WLTC, RTS95, and laboratory RDE cycles. Sub-23 nm particles were almost not identified within the engine cold-start phase and tended to be a hot-running pollutant favored by aggressive driving styles (frequent accelerations and high engine loads), fuel-cut during decelerations, and long idles. Lower testing temperature delayed the light-off of catalyst and, therefore, significantly reduced the formation of sub-23 nm particles within the engine warm-up stage. Lowering the detection limit to 10 nm is deemed to provide more public health protection since it will guide manufacturers to pay more attention to vehicle hot-running emissions.

Emissions from a Modern Euro 6d Diesel Plug-In Hybrid

Plug-in hybrid electric vehicles (PHEVs) are promoted as an alternative to conventional vehicles to meet European decarbonisation and air quality targets. However, several studies have shown that gasoline PHEVs present similar criteria and particulate emissions as their conventional gasoline counterparts. In the present work, we investigate the environmental performance of a modern plug-in hybrid Diesel-fuelled vehicle meeting the Euro 6d standard under a large variety of driving patterns, ambient temperatures, and battery states of charge (SOC). Emissions of regulated pollutants, currently unregulated pollutants, and CO2 were measured in the laboratory and following various on-road routes. The vehicle, whose electric range was 82 km, presented emissions below the Euro 6 regulatory limits in all the different driving cycles performed at 23 °C and all the on-road tests at the different battery SOC. The emissions were lower than the average of the conventional Diesel vehicles tested at JRC in 2020–2021 for all the SOC tested, the exception being solid particle number emissions >23 nm (SPN23) emissions that were comparable at all SOC. Moreover, the emissions obtained with the high voltage battery fully charged during on-road tests were comparable to those obtained with the battery at the minimum SOC for the entire test (ca. 91 km) as well as for the urban section (ca. 36 km). Overall, NOx and SPN23 emissions increased at lower temperatures, showing that at very low temperatures, there is no benefit in terms of particulate emissions from the electric range. Finally, it is shown that the emissions of N2O, the only unregulated pollutant presenting relevant emissions for this vehicle, and which are of catalytic nature, were proportional to the utilisation of the internal combustion engine. The scope of the manuscript is thus to deepen the knowledge on the emission performances of Diesel PHEVs through the systematic testing of a modern representative of this class of vehicles in a wide range of driving and environmental conditions.

On-Road and Laboratory Emissions from Three Gasoline Plug-In Hybrid Vehicles-Part 2: Solid Particle Number Emissions

Plug-in hybrid electric vehicles (PHEVs) are a promising technology for reducing the tailpipe emissions of CO2 as well as air pollutants, especially in urban environments. However, several studies raise questions over their after-treatment exhaust efficiency when their internal combustion engine (ICE) ignites. The rationale is the high ICE load during the cold start in combination with the cold conditions of the after-treatment devices. In this study, we measured the solid particle number (SPN) emissions of two Euro 6d and one Euro 6d-TEMP gasoline direct injection (GDI) PHEVs (electric range 52–61 km) all equipped with a gasoline particulate filter, in the laboratory and on-road with different states of charge of the rechargeable electric energy storage system (REESS) and ambient temperatures. All vehicles met the regulation limits but it was observed that, even for fully charged REESS, when the ICE ignited SPN emissions were similar or even higher in some cases compared to the operation of these vehicles solely with their ICE (discharged REESS) and also when compared to conventional GDI vehicles. On-road SPN emission rate spikes during the first 30 s after a cold start were, on average, 2 to 15 times higher with charged compared to discharged REESS due to higher SPN concentrations and exhaust flow rates. For one vehicle in the laboratory under identical driving conditions, the ICE ignition at high load resulted in 10-times-higher SPN emission rate spikes at cold-start compared to hot-start. At −10 °C, for all tested vehicles, the ICE ignited at the beginning of the cycle even when the REESS was fully charged, and SPN emissions increased from 30% to 80% compared to the cycle at 23 °C in which the ICE ignited. The concentration of particles below 23 nm, which is the currently regulated lower particle size, was low (≤18%), showing that particles larger than 23 nm were mainly emitted irrespective of cold or hot engine operation and ambient temperature.

Nucleation-accumulation mode trade-off in non-volatile particle emissions from a small non-road small diesel engine.

Small (< 8kW) non-road engines are a significant source of pollutants such as particle number (PN) emissions. Many small non-road engines do not have diesel particulate filters (DPFs). They are so designed that air-fuel ratio (AFR) can be adjusted to control visible diesel smoke and particulate matter (PM) resulting from larger accumulation mode particles. However, the effect of AFR variation on smaller nucleation mode nanoparticle emissions is not well understood. Several studies on larger engines have reported a trade-off between smaller and larger particles. In this study, AFR was independently varied over the entire engine map of a naturally aspirated (NA) non-road small diesel engine using forced induction (FI) of externally compressed air. AFR's ranged from 57 to 239 compared to the design range of 23-92 for the engine, including unusually high AFR's at full-load operation, not previously reported for conventional combustion. As expected, larger accumulation mode particles were lowered (up to 15 times) for FI operation. However, the smaller nucleation mode nanoparticles increased up to 15 times. Accumulation mode particles stopped decreasing above an AFR threshold while nucleation particles continuously increased. In-cylinder combustion analysis showed a slightly smaller ignition delay and higher burn rate for FI cases relative to NA operation. Much higher peak cylinder pressures were accompanied by much lower combustion and exhaust gas temperatures (EGT), due to higher in-cylinder mass during FI operation. Peak nucleation mode emissions were shown to be negatively correlated to EGT for all the data, collapsing on a single curve. This is consistent with some other studies reporting increased nucleation mode emissions (and higher accumulation mode particles) with decreased load, lower speed, lower EGR, advanced combustion phasing, and higher injection pressure, all of which reduce EGT. The nucleation-accumulation trade-off has been explained by the 'adsorption hypothesis' by some investigators. In the current work, an alternative/supplemental argument has been made for the possibility that lower cylinder temperatures during the late-burning phase (correlated to lower EGT) phase hampers oxidation of nucleation mode particles and increases nucleation mode emissions.

Impact of Active Diesel Particulate Filter Regeneration on Carbon Dioxide, Nitrogen Oxides and Particle Number Emissions from Euro 5 and 6 Vehicles under Laboratory Testing and Real-World Driving

Particulate mass concentration is a crucial parameter for characterising air quality. The diesel particulate filter (DPF) is the primary technology used to limit vehicle particle emissions, but it needs periodic cleaning, a process called regeneration. This study aims to assess the impact of active DPF regeneration on the performance and emissions of Euro 5 and 6 vehicles. The study examined both carbon dioxide (CO2) and pollutant (nitrogen oxides (NOx) and particle number (PN)) emissions for eight vehicles tested in the laboratory and on the road. Apart from the DPF, a wide range of emission control systems was covered in this experimental campaign, including exhaust gas recirculation (EGR), diesel oxidation catalyst (DOC), lean NOx trap (LNT) and selective catalytic reduction (SCR) catalyst, revealing the different impacts on NOx emissions. The regeneration frequency and duration were also determined and used to calculate the Ki factor, which accounts for the emissions with and without regeneration, weighted over the distance driven between two consecutive regeneration events. Based on these outcomes, representative emission factors (EF) were proposed for the regeneration phase only and the complete regeneration interval. In addition, the effect of regeneration on efficiency was estimated and compared with other energy consumers. The results indicated a significant impact of DPF regeneration on CO2, NOx and PN emissions, higher in the case of driving cycle testing in the laboratory. The relevant mechanisms behind the elevated emission levels were analysed, focusing on the regeneration period and the test phase following immediately after. The calculation of the Ki factor and the comparison with the official values revealed some weaknesses in its application in real-world conditions; to overcome these, new NOx EF values were calculated, depending on the emission control system. It was revealed that Euro 6 vehicles equipped with SCR could comply with the applicable limits when considering the complete regeneration interval. Finally, it was indicated that the DPF regeneration impact on vehicle efficiency is similar to that of driving with the air conditioning (A/C) system and headlights on.

Assessment of particle and gaseous emissions and reductions from gasoline direct injection passenger car and light-duty truck during passive regeneration

This study evaluated the effectiveness of two passive regenerating gasoline particulate filters (GPFs) on reducing both gaseous and particle phase pollutants from a gasoline direct inject (GDI) passenger car (PC) and light-duty truck (LDT). In the absence of filter regeneration, observations from this study are consistent with other studies demonstrating how particle number (PN), particulate matter (PM), and black carbon (BC) emissions were reduced from the two vehicles with the use of GPFs. The significance of this study was to demonstrate the ability of the GPF to mitigate gaseous and particulate pollutants during severe passive filter regeneration, which was often observed on the LDT during aggressive US06 drive cycle testing. Partial filter regeneration happened on the LDT during some FTP-75 tests, as well as on the PC during some US06 drive cycles, however, this did not impact the GPF filtration efficiency (FE) to reduce particulate and gaseous pollutants. Using a cleaner fuel with lower overall tailpipe PM emissions could potentially lead to more frequent partial regenerations. This could produce the benefit of lower exhaust back pressure during and immediately after regeneration but still provide sufficient reduction in both particle and gaseous emissions.

Particle number emissions from fully warmed gasoline vehicles at various ambient temperatures

Road vehicles have become the primary source of fine particles in many large cities. Vehicle hot-start PN emissions at various ambient temperatures were studied previously. Still, these studies used the same rolling resistance setting at different ambient temperatures and the tests at various ambient temperatures have similar PN emissions. Vehicles get larger resistance at cold ambient temperatures, so this experimental setting (same resistance at various ambient temperatures) is beyond the natural conditions. To evaluate how ambient temperatures affect the PN emissions from fully warmed vehicles, two vehicles were tested at four ambient temperatures: −10 °C, 0 °C, 23 °C, and 40 °C. Vehicle resistance variations under different ambient temperatures were taken into consideration. The observed results proved that PN emission would significantly deteriorate under cold conditions even when the vehicles are thoroughly warmed. The PN emission factor at −10 °C could be six times higher than at 23 °C. The deteriorated PN emission is caused by enhanced fuel enrichment and GPF regeneration, and larger vehicle resistance under cold ambient temperatures is the underlying reason for the increased PN emission. For the first time, this study proved that PN emission from fully warmed vehicles would significantly deteriorate when the ambient temperature decreases. The results could be used for emission models, inventory, and regulations.

Effects of a start-stop system for gasoline direct injection vehicles on fuel consumption and particulate emissions in hot and cold environments

Engine start-stop (S&S) technology has been substantially incorporated into modern vehicles to save fuel during idling in congested urban areas because fuel economy regulations have become more stringent. However, the potential for increasing particle emissions after engine restarts, especially in cold environments, is of great concern. To investigate the effects of S&S systems on fuel consumption and tailpipe emissions, a chassis dynamometer was employed to measure the fuel consumption, particulate matter (PM), solid particle number (PN), particle number size distribution and black carbon (BC) for a typical gasoline direct injection vehicle when the S&S was on (S&S-on) and when the S&S was off (S&S-off) according to the worldwide harmonized light-duty test cycle in both hot (28 °C) and cold (5 °C) environments. S&S operation resulted in 3.1–4.3% fuel-savings at 28 °C but had a tendency to increase particulate emissions, especially of BC (21.8–31.8%) and PM (19.2–32.8%). Although PN emissions with S&S-on over the entire cycle were slightly lower than those with S&S-off, more particles were emitted during the engine restart moments. In a cold environment, the fuel-savings advantage of the S&S system was weakened, and the negative impacts on the particle emissions during the restart moment worsened. The S&S system resulted in higher abundances of accumulation mode particles, especially under cold ambient conditions. The relationship between the PN reduction rates and idling segments was determining to be exponential. Our results indicate that the S&S system, which may increase particle emissions during restarts, does save fuel, and that a comprehensive evaluation of the system in cold environments is needed to determine the serviceability of new engine technologies and after-treatments.

Aircraft engine particulate matter emissions from sustainable aviation fuels: Results from ground-based measurements during the NASA/DLR campaign ECLIF2/ND-MAX

The use of alternative jet fuels by commercial aviation has increased substantially in recent years. Beside the reduction of carbon dioxide emission, the use of sustainable aviation fuels (SAF) may have a positive impact on the reduction of particulate emissions. This study summarizes the results from a ground-based measurement activity conducted in January 2018 as part of the ECLIF2/ND-MAX campaign in Ramstein, Germany. Two fossil reference kerosenes and three different blends with the renewable fuel component HEFA-SPK (Hydroprocessed Esters and Fatty Acids Synthetic Paraffinic Kerosene) were burned in an A320 with V2527-A5 engines to investigate the effect of fuel naphthalene/aromatic content and the corresponding fuel hydrogen content on non-volatile particle number and mass emissions. Reductions up to 70% in non-volatile particle mass emission compared to the fossil reference fuel were observed at low power settings. The reduction trends to decrease with increasing power settings. The fuels showed a decrease in particle emission with increasing fuel hydrogen content. Consequently, a second fossil fuel with similar hydrogen content as one of the HEFA blends featured similar reduction factors in particle mass and number. Changes in the fuel naphthalene content had significant impact on the particle number emission. A comparison to in-flight emission data shows similar trends at cruise altitudes. The measurements highlight the importance of individual fuel components in regulating engine emissions, particularly at the low thrust settings typically employed during ground operations (e.g. during idle and taxi). Therefore, when selecting and mixing SAF blends to meet present fuel-certification standards, attention should be paid to minimizing complex aromatic content to achieve the greatest possible air quality and climate benefits.

Emissions of Euro 6 Mono- and Bi-Fuel Gas Vehicles

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives in Europe. Most studies on emissions factors are based on old technology CNG and LPG fueled vehicles. Furthermore, there are not many data at low ambient temperatures, on-road driving, or unregulated pollutants, such as ammonia (NH3). In this study we measured the emissions of one Euro 6b CNG light commercial vehicle, one Euro 6b and one Euro 6d-Temp bi-fuel LPG passenger car, one Euro 6d-Temp bi-fuel CNG passenger car, and four Euro 6d-Temp CNG passenger cars. Tests included on-road testing and worldwide harmonized light vehicles test cycles (WLTC) in the laboratory with cold and hot engine, at 23 °C and −7 °C. The results showed 10–23% CO2 savings in gas modality compared to gasoline, lower CO and particle number emissions, and relatively similar total and non-methane hydrocarbons and NOx emissions. The ammonia emissions were high for all vehicles and fuels; higher than gasoline and diesel vehicles. The results also showed that, following the introduction of the real-driving emissions regulation, even though not applicable to the examined vehicles, Euro 6d-Temp vehicles had lower emissions compared to the Euro 6b vehicles.

Effect of lubricating oil characteristics on solid particle number and CO2 emissions of a Euro 6 light-duty compressed natural gas fuelled vehicle

Lubricant oil affects the fuel consumption and exhaust emissions of passenger cars. Oil reduces the friction in combustion engines, yet simultaneously some lubricating oil is exhausted from the engine. The fugitive lubricant oil results in < 30 nm solid particle number (SPN) emissions in the exhaust gas. The characteristics and formation path of the small particles is not well known, but as the SPN regulation is extending down to 10 nm size range, they cannot be neglected. Vehicles using compressed natural gas (CNG) fuel are known to emit solid particles in the < 23 nm size range. Here we studied the emissions of a CNG-fuelled Euro 6 light-duty vehicle using different lubricants. The lubricant characteristics had a strong effect on < 23 nm SPN emissions. A high ash, high volatility lubricant was shown, to alter the SPN population also in > 10 nm and even > 23 nm size range, thus, underlining the importance of the lubricant quality. The difference between the high volatility lubricant and the two tested modern lubricants was most evident at high temperature, high speed driving, while the emissions at the start of the cycle were of the same order of magnitude for all oils. The lubricant formulation was also shown to affect the vehicle CO2 emissions. The vehicle CO2 emissions in the tests driven with the high volatility lubricant oil exceeded the emissions with optimized lubricant oil by as much as 2%. Thus, the right lubricant choice can lead to fuel savings in CNG-fuelled vehicles. The presented results demonstrate the origin of the < 23 nm SPN in CNG-fuelled vehicles.

Characterizing the particle number emissions of light-duty gasoline vehicles under different engine technologies and driving conditions

Vehicle particle number (PN) emissions have attracted increasing public attention due to their severe influence on human health. In this study, we selected 35 light-duty gasoline vehicles (LDGVs) with gasoline direct injection (GDI) and multi-port fuel injection (MPFI) engines to elucidate the main factors influencing PN emissions. Via real driving emission (RDE) and chassis dynamometer tests, we quantified the impact of engine technology, emission standards, engine-start conditions and engine load on vehicle PN emissions. The RDE test results indicated that GDI vehicles generated higher PN emissions than those of MPFI vehicles under hot-running conditions. MPFI vehicle PN emissions were greatly affected by rapidly changing driving conditions, especially vehicles equipped with automatic start-stop systems. In regard to China 6 GDI vehicles equipped with a gasoline particle filter (GPF), their PN emissions were usually low, and peak PN emissions could mainly be attributed to GPF regeneration. Engine manufacturers should optimize GPF regeneration conditions to further reduce particulate emissions. Furthermore, the analysis results of PN emissions for different road types indicated that PN emissions were related to vehicle driving conditions. The vehicle specific power (VSP) could be used as an important explanatory variable to characterize the PN emission rate when distinguishing different engine technologies and emission standards. A real-world LDGV VSP-based PN emission rate was suggested based on the RDE test dataset. The VSP-based emission rate could be considered to more accurately quantify vehicle PN emissions and support the formulation of urban vehicle particle emission control policies.

Effect of Tampering on On-Road and Off-Road Diesel Vehicle Emissions

Illegal manipulation (i.e., tampering) of vehicles is a severe problem because vehicle emissions increase orders of magnitude and significantly impact the environment and human health. This study measured the emissions before and after representative approaches of tampering of two Euro 6 Diesel light-duty passenger cars, two Euro VI Diesel heavy-duty trucks, and a Stage IV Diesel non-road mobile machinery (NRMM) agricultural tractor. With tampering of the selective catalytic reduction (SCR) for NOx, the NOx emissions increased by more than one order of magnitude exceeding 1000 mg/km (or mg/kWh) for all vehicles, reaching older Euro or even pre-Euro levels. The tampering of the NOx sensor resulted in relatively low NOx increases, but significant ammonia (NH3) slip. The particle number emissions increased three to four orders of magnitude, reaching 6–10 × 1012 #/km for the passenger car (one order of magnitude higher than the current regulation limit). The tampered passenger car’s NOx and particle number emissions were one order of magnitude higher even compared to the emissions during a regeneration event. This study confirmed that (i) tampering with the help of an expert technician is still possible, even for vehicles complying with the current Euro standards, although this is not allowed by the regulation; (ii) tampering results in extreme increases in emissions.

Impact of Vehicle Soot Agglomerates on Snow Albedo

Snow covers are very sensitive to contamination from soot agglomerates derived from vehicles. A spectroradiometric system covering a wavelength from 300 to 2500 nm with variable resolution (from 2.2 to 7.0 nm) was used to characterize the effect of soot derived from a diesel vehicle whose exhaust stream was oriented towards a limited snowed area. The vehicle was previously tested in a rolling test bench where particle number emissions and size distributions were measured, and fractal analysis of particle microscopic images was made after collecting individual agglomerates by means of an electrostatizing sampler. Finally, the experimental results were compared to modelled results of contaminated snow spectral albedo obtained with a snow radiative transfer model developed by our research group (OptiPar) and with other models. Both experimental and modelled results show that increasingly accumulated soot mass reduces the snow albedo with a constant rate of around 0.03 units per mg/kg, with a predominant effect on the UV-VIS range. Based on the small size of the primary particles (around 25 nm), the Rayleigh-Debye-Gans approximation, further corrected to account for the effect of multiple scattering within the agglomerates, was revealed as an appropriate technique in the model.

Pollutant emissions from Euro 6 light duty vehicle tested under steady state and transient operation on a roller test bench with hydrogenated paraffinic and biodiesel fuels

The effort to implement more environmental-friendly fuels has been enhanced not only by the desire to reduce the greenhouse effects but also for public health issues. This paper studies the effects on pollutant emissions from a light-duty Euro 6 vehicle with four types of fuel: diesel (fossil origin, used as reference), biodiesel (renewable origin), Gas-to-Liquid (fossil origin) and farnesane (renewable origin). Both stationary engine and real-world driving cycles are studied. First, each fuel was tested in stationary modes in a vehicle test-bench and then tested in a realistic driving cycle with the same vehicle. This allows the separation the transient effects of the driving cycle from stationary results. Stationary tests lead to engine emission maps and driving cycle tests allow weighting the importance of each stationary condition during a realistic route. Instantaneous and cumulative CO, THC (total hydrocarbon), NOx and PN (particle number) emissions on route were obtained. The fuel that presented a highest level of emissions at stationary conditions was, for CO, diesel, for THC, diesel, for NOx, biodiesel and for PN, diesel. The behaviour of fuels during the driving cycles, from less pollutant to more pollutant, was: for CO, diesel, farnesane, GTL and biodiesel; for THC, GTL, farnesane, biodiesel, diesel. For NOx, farnesane and diesel (very similar values), GTL and biodiesel; for PN, GTL, biodiesel, farnesane and diesel.

An experimental investigation of particle and NOx emissions for a non-road diesel engine equipped with an integrated DOC + CDPF + SCR aftertreatment system during different operations.

An integrated aftertreatment system consisting of diesel oxidation catalyst (DOC), catalytic diesel particulate filter (CDPF), and selective catalytic reduction (SCR) is an effective way of reducing both NOx and particulate matter (PM). In this paper, the effect of DOC + CDPF + SCR on NOX and particle emissions is investigated during different operations to assess applicability of this aftertreatment for meeting more rigorous non-road emissions standard. Meanwhile non-negligible issue about regeneration emission is studied. The results show that the DOC + CDPF have no significant effect on NOx but increase the NO2/NOx ratio which is correlated with load. SCR is the main NOx reduction device with average efficiency of 86.5% for steady-state operations. Meanwhile, NH3 slip is lower than 16ppm. During cold and hot non-road transient cycles (NRTCcycles), average NOx efficiencies are 56.7% and 57.8%, respectively, along with NH3 slip below 10ppm. DOC + CDPF + SCR maintain filtration efficiency over 97% and 99% for PM and particle number (PN) for either steady-state operation or NRTCcycle, but particle size distributions change. Compared with the original emissions, NOx, PM, and PN emission factors are all below non-road China-IV limit after equipping with DOC + CDPF + SCR. However, during regeneration the aftertreatment does not maintain a high filtration performance but becomes particle generator. The penetration of nuclear particles and decomposition of agglomerated particles lead to high CDPF-out PN of 1.5 × 107 #/cm3-3.5 × 107 #/cm3. During regeneration, accumulated NOx is negligible, but the PM is 121.6 and 44.5 times higher than cold and hot NRTCcycles, respectively. In summary, DOC + CDPF + SCR is excellent way to improve non-road emissions but low SCR efficiency at low-temperature and high accumulated PM during regeneration process should be further addressed.

Spray and engine performance of cerium oxide nanopowder and carbon nanotubes modified alternative fuel

This work aims to experimentally investigate and demonstrate the impacts of using Cerium Oxide (CeO2) and multi-wall carbon nanotube (CNT) blended with the alternative fuel, which is gas-to-liquid fuel (GTL) in this study, compared to diesel fuel (DF) on engine performance and study the macroscopic spray characteristics through a Constant Volume Vessel (CVV). Results demonstrate Cerium Oxide nanopowder and carbon nanotubes have very limited impacts on the average cone angle of gas-to-liquid fuel and diesel fuel. Cerium Oxide nanopowder and carbon nanotubes can individually reduce spray penetration during injection under a small ambient pressure when blended with diesel fuel, whilst the effect on gas-to-liquid fuel is less significant because the smaller density and lighter compositions of gas-to-liquid fuel promote its breakup process. In the post-injection period, carbon nanotubes increases the spray penetration of gas-to-liquid fuel, because gas-to-liquid fuel molecules are smaller than diesel fuel. Consequently, more gas-to-liquid fuel molecules stay inside the carbon nanotubes, which can only evaporate through two ends, and thus results in an overall reduced evaporation rate. Moreover, experiments also demonstrate that the average cone angle is independent of rail pressure, but it can be reduced by decreasing ambient pressure and increasing ambient temperature. During injection, both ambient pressure and rail pressure can influence the spray penetration, whilst after the end of injection, only ambient temperature has an effect on it. The engine experiment indicates that Cerium Oxide nanopowder can reduce nitrogen oxides, unburnt hydrocarbons and particulate number emissions simultaneously for both diesel fuel and gas-to-liquid fuel due to its catalysis at high-temperature conditions, whilst carbon nanotubes has a weaker effect on reducing nitrogen oxides and particulate number for gas-to-liquid fuel than diesel fuel.