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Research on ammonia emissions from three-way catalytic converters based on small sample test and vehicle test
Abstract
In this paper, a combination of catalyst sample evaluation and vehicle test is used to deeply study the formation mechanism of ammonia in the process of three-way catalytic reaction, and further explore the influence of catalyst formulation and aging on ammonia emissions. The catalytic sample test shows that CO reacts with terminal hydroxyl and bridging hydroxyl on the surface of the catalyst to generate H2 at low temperature, which then reduces NO to generate NH3. At high temperatures, CO reacts with water to generate H2, or hydrocarbon compounds in exhaust react with steam to generate hydrogen, and then H2 reacts with nitrogen oxides to generate NH3. On the one hand, the presence of water vapor can be prompted catalytic hydroxylation of materials and promote the reaction of the hydroxyl and bridging hydroxyl to improve the selectivity of NH3, on the other hand, as the competitive adsorption of H2O molecules and NO on the catalyst surface inhibits the reduction reaction between NH3 and NO, the consumption of NH3 molecules is reduced, and more NH3 vaporizes from the catalyst surface to the gas phase. The combination of Pd/Rh can effectively reduce the NH3 generation compared with the single Pd formulation. Ammonia emission can be effectively reduced by precisely controlling the air-fuel ratio of the engine and combining it with the catalytic converter which optimizes the ratio of precious metals.
... Nowadays, vehicles and networks have been insisted in the transportation system in smart cities. The intelligent transport system is the communication and the information technology which make the mobility management interface with the combination of other transports [22]. The usability of a traffic control system and traffic management reflects traffic patterns. ...
... Where A is considered as the focal length, then d O and d I are the distance from the camera to the object and image and h O and h I Are the height of the image and objects. The distance of the image and focal length are considered fixed based on the particular camera, which can be obtained from the information found in the camera [22]; if the object which needs to be detected is in focus, then it is determined as the focal length is equal to the distance of the image. ...
Intelligent Transportation System (ITS) idea was developed to improve road safety, traffic management efficiency, and environmental preservation. The fog-robotics Based Intelligent Transportation Systems integrate Internet of Vehicles (IoV) devices to Fog Computing (FC) centers, which process the data. On the other hand, providing massive data from widely distant devices causes network overhead and bottlenecks in Autonomous Driving and a drain on Energy Management. To fill this research gap, fog-robotics-based intelligent transportation systems are proposed to cover the line-of-sight direction for path adopting self-directed intelligent transportation. The Intelligent Transportation Systems with FC Techniques work towards the Fog Robotics Platform for making efficient fog-robotics Transportation Systems. The Proposed System has two function-alities; firstly, the analysis of automatic Fog-robotics transportation systems is introducing decentralized wireless sensor transfer assisted flocking autonomous driving for energy management of fog-robotics transportation systems. It Shows the Sensor activities as per the "scanning of the roadside meter." It enumerates speed control. Secondly, Artificial Intelligence Enabled Intelligent speed assistance is formed based on Vehicle Infrastructure Integration (VII). This Vehicle infrastructure integration is used to show the Smart highway, which is adaptable with the fog-robotics Transportation Systems. Although the formation of "Digital modeling and fabrication framework" procedural aspect employed to connect the "Fog-robotics Transportation Systems" and "Vehicle infrastructure integration." This Artificial Intelligence configuration is used to Enabled Intelligent speed assistance for controlling the car for their atmosphere. Finally, these rely on are consolidated with the position/navigation system, and the vehicle detection ratio is analyzed with the vehicle efficiency and economic activity for intelligent speed assistance. Multimedia Tools and Applications https://doi.
... Whole-vehicle fuel economy testing requires accurate measurements of whole-vehicle fuel consumption [27]. There are many hybrid bus energy subsystems, and the energy flow was complicated. ...
This paper took a new energy vehicle feedback system as the research object, aiming to study the energy recovery law of the new energy vehicle under braking feedback and taxiing feedback conditions. Firstly, the braking energy feedback control strategy and different forms of taxiing energy feedback were studied. Then the integration and application of braking energy recovery system were carried out on a pure electric bus and a hybrid electric bus, with each vehicle model corresponding to different integration and test schemes, which provided a guarantee for the relevant test of real vehicle environments. Finally, relevant vehicle experiments were carried out to test the impact of superposition and coordination strategies on the contribution rate of braking energy recovery under a typical Chinese city bus circle and compared the difference in vehicle energy consumption with and without taxi feedback strategy. The test results showed that the coordinated braking energy recovery control strategy can make more effective use of the maximum torque that can be fed back by the motor, and the fuel consumption of the taxiing feedback mode was lower than that of the no taxiing feedback mode under different driving conditions.
Gasoline engine vehicle emissions, such as nitrogen oxides (NOx), CO and hydrocarbons (HCs), are a major source of air pollution, and require improved emission control systems. By-product NH3 and N2O emissions, which come from low N2 selectivity in the emission control system, are also a major concern. The current study has comprehensively investigated the impact of the Pt-substitution in commercial Pd/Rh-based three-way catalyst (TWC) formulations with respect to catalytic performance. TWC performance was systematically evaluated with respect to the warm-up catalytic converter (WCC) and the under-floor catalytic converter (UCC). This included evaluating TWC activity under realistic simulated exhaust conditions including fuel-rich, stoichiometric and fuel-lean (0.99≤λ≤1.01). Pt-substituted TWCs outperformed Pd-based counterparts, regardless of the converter type (WCC or UCC), in CO, C3H6 and C3H8 oxidation and NO reduction reactions under the simulated exhaust conditions tested. Moreover, Pt-substituted TWCs exhibited significant stability upon hydrothermal aging at 1,050 °C. The results show that after aging the Pt-substituted catalyst retained higher N2 selectivity than the Pd-based TWC. Over Pd-based TWCs, N2 selectivity drastically dropped from 70–80% to 15–35% after aging, while Pt-substituted TWCs N2 selectivity dropped from 80–100% to only 60–80%. The key finding from this study is that Pt incorporation in a Pd/Rh TWC improves the emission control from gasoline vehicles in terms of both CO and HC oxidation and NOx reduction.
Transport sector decarbonisation is leading to increased demand for electrified powertrains including hybrid vehicles. The presence of an internal combustion engine and electric motor offer multiple performance and efficiency advantages. However, changes in the conditions that catalytic aftertreatment systems are subjected to can present challenges in meeting forthcoming emissions standards. This work investigated the three-way catalyst performance to abate regulated and unregulated emissions from a gasoline direct injection engine working under conditions related to hybrid vehicle operation. The focus on unregulated emissions of NH3 and N2O is of interest due to limited literature on their formation in conventional, and particularly hybrid, vehicle aftertreatment systems. Furthermore, the likelihood of their regulation when the EURO 7 emissions standards are introduced increases the pertinence of this work. For this particular engine and aftertreatment setup, it was found that starting the engine whilst the three-way catalyst temperature was below 150 ℃ led to an increase in tailpipe regulated emissions and N2O. Whilst, starting the engine when three-way catalyst temperatures were above 350 ℃ lead to tailpipe NH3 emissions. This was due to the selectivity of NO to form N2O at lower temperatures and NH3 at higher temperatures. For the case of the studied catalyst, a vehicle energy management strategy opting to start the engine with the three-way catalyst within a targeted temperature range allowed for a trade-off between regulated emissions, N2O and NH3. These findings are significant since it can be used to optimise hybrid vehicle control strategies minimising both regulated and unregulated emissions.
Pollution from vehicles is a serious concern for the environment and human health. Vehicle emission regulations worldwide have limits for pollutants such as hydrocarbons, CO, and NOx. The measurements are typically conducted at engine dynamometers (heavy-duty engines) sampling from the tailpipe or at chassis dynamometers (light-duty vehicles) sampling from the dilution tunnel. The latest regulations focused on the actual emissions of the vehicles on the road. Greenhouse gases (GHG) (such as CO2, CH4, N2O), and NH3 have also been the subject of some regulations. One instrument that can measure many gaseous compounds simultaneously is the Fourier transform infrared (FTIR) spectrometer. In this review the studies that assessed FTIRs since the 1980s are summarized. Studies with calibration gases or vehicle exhaust gas in comparison with well-established techniques were included. The main conclusion is that FTIRs, even when used at the tailpipe and not at the dilution tunnel, provide comparable results with other well-established techniques for CO2, CO, NOx, while for hydrocarbons, higher deviations were noticed. The introduction of FTIRs in the regulation needs a careful description of the technical requirements, especially interference tests. Although the limited results of prototype portable FTIRs for on-road measurement are promising, their performance at the wide range of environmental conditions (temperature, pressure, vibrations) needs further studies.
With a continuous increase in vehicle ownership, vehicle emissions have become one of the main sources of air pollution in China. Serious air pollution is a great threat to human health and life. The China VI regulations, which adopt strict particulate matter (PM) and nitrogen oxide (NOx) limitations, have been implemented. As one of the best technologies for measuring vehicle emissions, portable emission measurement systems (PEMSs) have gained attention. In this work, the characteristics of China VI heavy-duty vehicle emissions were investigated with a PEMS. The effects of road conditions on NOx, hydrocarbon (HC), carbon monoxide (CO), PM and particle number (PN) pollutants were analyzed based on distance-based emission factors. The results show that the gaseous pollutant levels of NOx, HC and CO for China VI vehicles are much lower than those for China V vehicles. The average distance-based emission factors of NOx CO and HC decreased by 88%, 98%, and 62.7%, respectively. Based on the power-based window method, the PEMS test results for NOx, HC and CO are 460 mg·(kWh)-1, 192 mg·(kWh)-1 and 37.5 mg·(kWh)-1, respectively. According to the PEMS tests, approximately 88%–95% of the particles are in the 10–100 nm class based on three typical operational modes, which represent approximately 0.08%–0.13% of the total particle mass. These heavy-duty vehicles can satisfy the requirements of the PEMS China VI standards. This study emphasizes the importance of obtaining real-world measurements of heavy-duty vehicles to improve the accuracy of emission factors in the development of emission inventories in China.
To meet the increasingly demanding emissions and fuel economy standards, the thermal management of the aftertreatment devices has recently become a priority in powertrain control. In particular, the longitudinal distribution of temperature in the three-way catalyst is a critically important variable to monitor for catalyst light-off control, thermal protection, and for diagnosing aging and degradation. However, such information is typically unavailable in production applications, due to the cost and reliability issues of instrumenting the three-way catalyst with multiple temperature sensors. This work focuses on the development and the experimental validation of a control-oriented, physics-based thermal model of a three-way catalyst for the purpose of real-time temperature monitoring. Starting from the governing equations in partial differential equation form, a model order reduction technique that combines proper orthogonal decomposition and collocation is developed. The sensitivity of the selection of the empirical basis functions is studied. To include the exothermic effect from chemical reactions, a fully connected artificial neural network is trained. The reduced-order model executes more than 100 times faster when compared to the use of standard numerical methods and commercial simulation software such as GT-Power, while providing comparable accuracy. Finally, to verify the proposed methodology, the model is calibrated and validated against experimental data collected by instrumenting a three-way catalyst with multi-point temperature measurements, and installed on an engine test bench.
Vehicles are considered to be an important source of ammonia (NH3) and isocyanic acid (HNCO). HNCO and NH3 have been shown to be toxic compounds. Moreover, NH3 is also a precursor in the formation of atmospheric secondary aerosols. For that reason, real-time vehicular emissions from a series of Euro 5 and Euro 6 light-duty vehicles, including spark ignition (gasoline and flex-fuel), compression ignition (diesel) and a plug-in electric hybrid, were investigated at 23 and −7°C over the new World harmonized Light-duty vehicle Test Cycle (WLTC) in the Vehicle Emission Laboratory at the European Commission Joint Research Centre Ispra, Italy. The median HNCO emissions obtained for the studied fleet over the WLTC were 1.4mgkm⁻¹ at 23°C and 6mgkm⁻¹ at −7°C. The fleet median NH3 emission factors were 10mgkm⁻¹ and 21mgkm⁻¹ at 23 and −7°C, respectively. The obtained results show that even though three-way catalyst (TWC), selective catalytic reduction (SCR), and NOx storage catalyst (NSC) are effective systems to reduce NOx vehicular emissions, they also lead to considerable emissions of the byproducts NH3 and/or HNCO. It is also shown that diesel light-duty vehicles equipped with SCR can present NH3 emission factors as high as gasoline light-duty vehicles at both, 23 and −7°C over the WLTC. Therefore, with the introduction in the market of this DeNOx technology, vehicular NH3 emissions will increase further.
The number of registrations of light duty hybrid electric vehicles has systematically increased over the last years and it is expected to keep growing. Hence, evaluation of their emissions becomes very important in order to be able to anticipate their impact and share in the total emissions from the transport sector. For that reason the emissions from a Euro 5 compliant hybrid electric vehicle (HV2) and a Euro 5 plug-in hybrid electric vehicle (PHV1) were investigated with special interest on exhaust emissions of ammonia, acetaldehyde and ethanol. Vehicles were tested over the World harmonized Light-duty Test Cycle (WLTC) at 23 and −7 °C using two different commercial fuels E5 and E10 (gasoline containing 5% and 10% vol/vol of ethanol, respectively). PHV1 resulted in lower emissions than HV2 due to the pure electric strategy used by the former. PHV1 and HV2 showed lower regulated emissions than conventional Euro 5 gasoline light duty vehicles. However, emissions of ammonia (2–8 and 6–15 mg km−1 at 22 and −7 °C, respectively), ethanol (0.3–0.8 and 2.6–7.2 mg km−1 at 22 and −7 °C, respectively) and acetaldehyde (∼0.2 and 0.8–2.7 mg km−1 at 22 and −7 °C, respectively) were in the same range of those recently reported for conventional gasoline light duty vehicles.
A study aiming to measure ammonia emissions from light duty vehicles has been performed in the Vehicle Emission Laboratory at the European Commission Joint Research Centre, Ispra, Italy. Ammonia, known for being toxic and dangerous for the environment, also contributes to the formation of particulate matter that has been related with adverse health and environmental effects.
Nine modern light duty vehicles tested over the New European Driving Cycle showed that ammonia emissions are considerable for gasoline and ethanol flexi-fuel vehicles and also for one diesel vehicle equipped with a selective catalytic reduction system, ranging from 4 mg/km to 70 mg/km. Real-time ammonia emission profiles were monitored at the tailpipe by a High Resolution Fourier Transform Infrared spectrometer during tests at 22 and/or -7 degrees Celsius. Ammonia emissions are thoroughly discussed and compared to those of its precursors, CO and NO, and other regulated compounds.
In this paper we report the first direct measurements of nitrogen
dioxide (NO2) in the UK using a vehicle emission remote
sensing technique. Measurements of NO, NO2 and ammonia
(NH3) from almost 70,000 vehicles were made spanning vehicle
model years from 1985 to 2012. These measurements were carefully matched
with detailed vehicle information data to understand the emission
characteristics of a wide range of vehicles in a detailed way. Overall
it is found that only petrol fuelled vehicles have shown an appreciable
reduction in total NOx emissions over the past 15-20
years. Emissions of NOx from diesel vehicles, including those
with after-treatment systems designed to reduce emissions of
NOx, have not reduced over the same period of time. It is
also evident that the vehicle manufacturer has a strong influence on
emissions of NO2 for Euro 4/5 diesel cars and urban buses.
Smaller-engined Euro 4/5 diesel cars are also shown to emit less
NO2 than larger-engined vehicles. It is shown that
NOx emissions from urban buses fitted with Selective
Catalytic Reduction (SCR) are comparable to those using Exhaust Gas
Recirculation for Euro V vehicles, while reductions in NOx of
about 30% are observed for Euro IV and EEV vehicles. However, the
emissions of NO2 vary widely dependent on the bus technology
used. Almost all the NOx emission from Euro IV buses with SCR
is in the form of NO, whereas EEV vehicles (Enhanced Environmentally
friendly Vehicle) emit about 30% of the NOx as
NO2. We find similarly low amounts of NO2 from
trucks (3.5-12t and >12t). Finally, we show that NH3
emissions are most important for older generation catalyst-equipped
petrol vehicles and SCR-equipped buses. The NH3 emissions
from petrol cars have decreased by over a factor of three from the
vehicles manufactured in the late 1990s compared with those manufactured
in 2012. Tables of emission factors are presented for
NOx, NO2 and NH3 together with
uncertainties to assist the development of new emission inventories.
To investigate the potential role of ammonia in ion chemistry of PM(2.5) aerosol, measurements of PM(2.5) (particulate matter having aerodynamic diameter < 2.5 microm) along with its ionic speciation and gaseous pollutants (sulfur dioxide (SO2), nitrogen oxides (NO(x)), ammonia (NH3) and nitric acid (HNO3)) were undertaken in two seasons (summer and winter) of 2007-2008 at four sampling sites in Kanpur, an urban-industrial city in the Ganga basin, India. Mean concentrations of water-soluble ions were observed in the following order (i) summer: SO4(2-) (26.3 microg m(-3)) > NO3(-) (16.8) > NH4+ (15.1) > Ca2+ (4.1) > Na+ (2.4) > K+ (2.1 microg m(-3)) and (ii) winter: SO4(2-) (28.9 microg m(-3)) > NO3(-) (23.0) > NH4+ (16.4) > Ca2+ (3.4) > K+ (3.3) > Na+ (3.2 microg m(-3)). The mean molar ratio of NH4+ to SO4(2-) was 2.8+/-0.6 (mostly > 2), indicated abundance of NH3 to neutralize H2SO4. The excess of NH4+ was inferred to be associated with NO3(-) and Cl(-). Higher sulfur conversion ratio (F(s): 58%) than nitrogen conversion ratio (F(n): 39%) indicated that SO4(2-) was the preferred secondary species to NO3(-). The charge balance for the ion chemistry of PM(2.5) revealed that compounds formed from ammonia as precursor are (NH4)2SO4, NH4NO3 and NH4Cl. This study conclusively established that while there are higher contributions of NH4+, SO4(2-) to PM(2.5) in summer but for nitrates (in particulate phase), it is the winter season, which is critical because of low temperatures that drives the reaction between ammonia and HNO3 in forward direction for enhanced nitrate formation. In summary, inorganic secondary aerosol formation accounted for 30% mass of PM(2.5) and any particulate control strategy should include optimal control of primary precursor gases including ammonia.
The objective of this study was to measure ammonia (NH3) emissions from modern technology vehicles since information is scarce aboutthis importantsource of particulate matter (PM) precursors. Test variables included the emission level to which the vehicle was certified, the vehicle operating conditions, and catalyst age. Eight vehicles with low-emission vehicle (LEV) to super-ultralow-emission vehicle (SULEV) certification levels were tested over the Federal Test Procedure (FTP75), a US06 cycle, a hot running 505, a New York City Cycle (NYCC), and a specially designed Modal Emissions Cycle (MEC01v7) using both as-received and bench-aged catalysts. NH3 emissions in the raw exhaust were measured by tunable diode laser (TDL) absorption spectroscopy. The results show that NH3 emissions depend on driving mode and are primarily generated during acceleration events. More specifically, high NH3 emissions were found for high vehicle specific power (VSP) events and rich operating conditions. For some vehicles, NH3 emissions formed immediately after catalyst light-off during a cold start.
Animal slurry storage is an important source of NH3 emission which has raised a high attention regarding its influence on air quality and environment health. There is an urgent need to develop an efficient, green and safe technology for reducing NH3 emission. This study introduced a novel method of reducing NH3 emission from dairy slurry storage using H2SO4 modified expanded vermiculite cover (H2SO4-VM1). Results showed that NH3 mitigation of 87% was achieved in the treatment of H2SO4-VM1 during 77 days of slurry storage, which could be mainly caused by conversion of free NH3 to NH4⁺ in acidified slurry surface and vermiculite layer, the cover barrier for gases emissions, NH4⁺ adsorption by vermiculite cover, and direct adsorption of free NH3 in the vermiculite layer. The NH3 mitigation of H2SO4-VM1 was comparable to that (90%) of the traditional method of H2SO4 acidification for slurry storage (H2SO4-AC1). The N2O emission, H2S emission, and H2SO4 consumption in H2SO-VM1 were 28, 93 and 39% lower than those in H2SO4-AC1, respectively. Economic cost calculated based on material input in H2SO-VM1 method was 0.40 USD m⁻² slurry. It’s suggested that H2SO4-VM1 can be a possible alternative for reducing NH3 emissions from animal slurry storage.
Oxygen storage capacity (OSC) of Pd/CeO2-ZrO2 was significantly improved by addition of transition metals (Ni, Fe, Co, Cu, Sn, Ga, In). Reducible transition metal, such as Ni, Fe, Cu, Co and Sn - doped Pd/CZ showed quite higher OSC than the theoretical value assumed the complete redox of Ce⁴⁺ ⇔ Ce³⁺ (250 mmol-O2 mol-CeO2⁻¹), suggesting the participation of transition metal in reversible oxygen release/sorption. Fe and Sn were effective additives to achieve high OSC property. No significant increase in the three-way catalytic activity of Pd/CeO2-ZrO2 under the stoichiometric conditions was achieved by the addition of transition metals. However, Ni, Co, Fe, and Ga – doped Pd/CeO2-ZrO2 showed higher TWC performance than Pd/CeO2-ZrO2 under the lean/rich perturbation conditions. From H2-TPR and FT-IR spectroscopy following CO adsorption, the role of Fe additive was concluded to be the creation of easily reducible Pd species interacting with Fe-doped CeO2-ZrO2 and then to be the stabilization of Pd species in the catalytically active reducing state under the reaction conditions.
This article introduces a physical model of a three-way catalytic converter oriented to engine cold-start conditions. Computational cost is an important factor, particularly when the modelling is oriented to the development of engine control strategies. That is why a one-dimensional one-channel real-time capable model is proposed. The present model accounts for two phases, gas and solid, respectively, considering not only the heat transfer by convection between both, but also the water vapour condensation and evaporation in the catalyst brick, which plays a key role during engine cold-start. Moreover, the model addresses the conductive heat flow, heat losses to the environment and exothermic reactions in the solid phase, as well as the convective heat flow in the gas phase. Regarding the chemical model, the oxidation of hydrocarbons and carbon monoxide is considered by means of the Langmuir–Hinshelwood mechanism. Three layers make up the model structure from a kinetic point of view, bulk gas, washcoat pores and noble metal in the catalyst surface. The model takes fuel-to-air ratio, exhaust gas mass flow, temperature, pressure and gas composition as inputs, providing the thermal distribution as well as the species concentration along the converter.
Ammonia emissions cause several negative impacts on the quality of air, water and soil, while secondary ammonia formed on three-way catalysts (TWCs) of gasoline vehicles has not been sufficiently investigated, especially in the developing countries. In this paper, tailpipe ammonia emissions from seven China-6 certified, low-mileage gasoline vehicles were measured over the World Harmonized Light-duty Test Cycle (WLTC). The results demonstrated that ammonia emissions from the seven test vehicles ranged from 0.65 ± 0.38 mg/km to 8.01 ± 3.12 mg/km. A comparison with the emission factors reported in other research indicates that these China-6 certified vehicles emitted similar or less ammonia emissions compared to the vehicles certified to older EU and federal regulations. The ammonia emissions from the test vehicles showed very weak linkage with their engine or transmission technologies. For all the test vehicles, the vast majority of ammonia emissions were emitted within the engine warm-up period due to already lighted-off catalysts but still enriched air/fuel mixtures. No ammonia emissions were noticed within any engine-start events. The masses of ammonia-converted ammonium salts were estimated assuming that all the tailpipe ammonia emissions will transform into ammonium nitrate and ammonium sulfate, and compared to the primary PM emissions measured with filters. The masses of salts were drastically higher than the primary PM, which underscored the significance of vehicle-related ammonia emissions as a key ambient PM contributor.
Motor vehicle ammonia (NH3) emissions have attracted increasing attention for their potential to form secondary aerosols in urban atmospheres. However, vehicle NH3 emission factors (EFs) remain largely unknown due to a lack of measurements. Thus, we conducted detailed measurements of NH3 emissions from eighteen Euro 2 to Euro 5 light-duty gasoline vehicles (LDGVs) in Shanghai, China. The distance- and fuel-based NH3 EFs average 29.2 ± 24.1 mg∙km-1 and 0.49 ± 0.41 g∙kg-1, respectively. The average NH3-to-CO2 ratio is 0.41 ± 0.34 ppbv∙ppmv-1. The measurements reveal that NH3 emissions from LDGVs are strongly correlated with both vehicle specific power (VSP) and the modified combustion efficiency (MCE); these relationships were used to predict LDGV NH3 EFs via a newly developed model. The predicted LDGV NH3 EFs under urban and highway driving cycles are 23.3 mg∙km-1 and 84.5 mg∙km-1, respectively, which are consistent with field measurements. The NH3 EF has decreased by 32% in average since the implementation of vehicle emission control policies in China five years ago. The model presented herein more accurately predicts LDGV NH3 emissions, contributing substantially to the compilation of NH3 emission inventories and prediction of future motor vehicle emissions in China.
Rh-based catalysts were prepared by various methods and it was found that preparation methods play an important role in metal-support interaction (MSI) control which affects the catalytic performance of catalyst. The results suggest that the catalytic reduction of NO is mainly achieved by C3H6 in exhaust and H2 generated from the water-gas shift reaction as well as the steam reforming of C3H8 and CH4. Concentration of water in reaction stream has a significant influence on the water-gas shift and steam reforming reactions. The removal of C3H6 is accomplished by oxygen-induced oxidation instead of steam reforming reaction. In addition, Rh/ceria interactions promote the formation of active oxygen species and surface oxygen vacancy that respectively favors CO oxidation and NO reduction with a high N2 selectivity. Rh@CeO2 system shows high thermal stability due to Rh/ceria interaction.
Total Organic Gases (TOG) emissions from motor vehicles include air toxic compounds and contribute to formation of ground-level ozone and secondary organic aerosol (SOA). These emissions are known to be affected by temperature; however previous studies have typically focused only on the temperature dependence of total emission factors and select toxic compounds. This study builds on the previous research by performing an evaluation of a comprehensive set of gas-phase organic compounds present in gasoline motor vehicle exhaust. A fleet of five vehicles using port fuel injection engine technology and running on E10 fuel were tested. Overall, three temperatures (0, 20 and 75oF; or -18, -7 and 24oC), two driving conditions (urban-FTP75 and aggressive driving-US06) and 161 compounds were evaluated; the emissions distributions were used to construct speciation profiles for each driving cycle and temperature. Overall, the speciation results indicated a significant increase in alkane and methane content, and decrease in alcohol, aldehyde and ketone content with decreasing temperature. These were verified using a statistical significance test. The fraction and composition of Mobile Source Air Toxics (MSATs) were significantly affected by temperature for both driving cycles. The ozone forming potentials of these profiles were evaluated using the maximum incremental reactivity (MIR) scale. Aromatic content was predicted to be a major driver behind the ozone forming potentials. Additionally, the decreasing ozone potential could be attributed to increased methane fractions with increasing temperature.
Ammonia is a reactive nitrogen compound (RNC - nitrogen-based gaseous molecules with multiple adverse impacts on human health and the biosphere). A three-way catalyst can produce substantial quantities of ammonia through various reaction pathways. This study presents a brief literature review, and presents experimental data on ammonia emissions from seven Euro 5 passenger cars, using different gasoline fuels and a CNG fuel. All vehicles were tested on a chassis dynamometer over the New European Driving Cycle. For six of the vehicles, ammonia was quantified directly at tailpipe (using two different analyzers); emissions from one vehicle were subjected to Fourier Transform Infra-Red (FTIR) analysis. Emissions of ammonia from these vehicles were generally low in comparison to other chassis dynamometer studies, perhaps attributable to the favorable laboratory test conditions and the age of the vehicles. Transient data revealed small but significant differences in ammonia emissions, including the time of the initial ammonia surge, depending on the test fuel and the fuel injection strategy. A range of metrics were examined to determine possible correlations between ammonia and other pollutants. No significant correlations were found; there was, however some evidence of a trade-off relationship between ammonia and NOx. An analysis of ammonia emissions in the context of RNC emissions revealed ammonia to make up roughly 18% of the RNCs released over the duration of the test cycle. Thus, the ammonia emissions observed here were low, but non-trivial, and the issue of automotive ammonia emissions and impacts on air quality is an important research direction.
Analysis of non-legislated engine-emission components, with different exhaust-gas after-treatment techniques, is an important air quality objective. This paper reports the results for various nitrogen oxides, ammonia and differentiated hydrocarbons emitted at part load from a small 4-S SI-engine. It was operated with gasoline, with CNG *) and with two different three-way catalytic converters. CNG produces less HC and less aromatics. But the HC conversion rate is insufficient. This is due to the lower exhaust gas temperatures, at part load with CNG, and due to the higher stability of light HCs. CNG affects the λ-regulation window, of the investigated system, such that the NOx conversion rate is lowered. In the rich domain of the λ-regulation window, the NO & NOx emissions after catalyst were lowest, while the NH3 formation was most intense, and vice versa. The catalyst type: precious metal, and its content, influences the conversion rates and emissions of the investigated components during light-off.
The aim of this paper was to explore the influence of CNG fuel on emissions from light-duty vehicles in the context of the new Euro 6 emissions requirements and to compare exhaust emissions of the vehicles fueled with CNG and with gasoline. Emissions testing was performed on a chassis dynamometer according to the current EU legislative test method, over the New European Driving Cycle (NEDC). Additional tests were also performed on one of the test vehicles over the World Harmonized Light Vehicles Test Cycle (WLTC) according to the Global Technical Regulation No. 15 test procedure. The focus was on regulated exhaust emissions; both legislative (CVS-bag) and modal (continuous) analyses of the following gases were performed: CO (carbon monoxide), THC (total hydrocarbons), CH4 (methane), NMHC (non-methane hydrocarbons), NOx (oxides of nitrogen) and CO2 (carbon dioxide). Furthermore, unregulated exhaust emissions were also examined in certain cases: particle number and mass, as well as emissions of NH3 (ammonia), NO (nitrogen monoxide) and NO2 (nitrogen dioxide). The results showed a range of differences in terms of regulated emissions, particulate matter and ammonia emissions, and also in the composition of the NOx in the exhaust gas (i.e. the NO:NO2 ratio). Emissions of both CO2 and particulates were markedly lower when running on CNG. Emissions from the two phases of the NEDC and the four phases of the WLTC were briefly analysed.
Vehicular ammonia emissions are currently unregulated, even though ammonia is harmful for a variety of reasons, and the gas is classed as toxic. Ammonia emissions represent a serious threat to air quality, particularly in urban settings; an ammonia emissions limit may be introduced in future legislation. Production of ammonia within the cylinder has long been known to be very limited. However, having reached its light-off temperature, a three-way catalyst can produce substantial quantities of ammonia through various reaction pathways. Production of ammonia is symptomatic of overly reducing conditions within the three-way catalyst (TWC), and depends somewhat upon the particular precious metals used. Emission is markedly higher during periods where demand for engine power is higher, when the engine will be operating under open-loop conditions. The air-to-fuel ratio, cylinder temperature and rate of availability of carbon monoxide and nitrogen monoxide all correlate to varying degrees with ammonia production. In addition to a literature review, this study presents ammonia emissions data from three European passenger cars, using three different fuels, with varying physicochemical characteristics and carbon:hydrogen ratios, namely gasoline, LPG and CNG. All vehicles were tested on BOSMAL's chassis dynamometer over the New European Driving Cycle, with undiluted ammonia quantified directly at tailpipe. Both cycle mean emission factors and second-by-second data are presented. The results indicate a degree of correlation between ammonia emission and demand for engine power, for example upon commencing acceleration and following gear shifts. Emission over the entire driving cycle was found to vary depending on the fuel used, and between the three vehicles used in this study. One vehicle emitted 93 % more ammonia when operating on gasoline than on CNG; the other vehicle emitted 2 % more ammonia when running on LPG than on gasoline. A simple numerical correction implied that the lower carbon:hydrogen ratio was at least partially responsible for the minimal ammonia emissions observed when running on this fuel.
Gasoline engines have been widely used as engineering machinery, automobile and shipping power equipment due to their excellent drivability and economy. At the same time, gasoline engines are major contributors to various types of air pollutants such as carbon monoxide (CO), oxides of nitrogen (NOx), and other harmful compounds. With the increasing concern of environment and more stringent government regulation on exhaust emissions, the reduction in engine emissions such as particulate matter and NOx is a major research objective in engine development. In this article the effect of heating the catalytic converter on emission characteristic of automotive vehicles in its starting phase of combustion has been studied. In this work, the emission characteristic of hydrocarbons has been improved from 800 to 15 ppm, CO from 4 to 0.07 (V/V%) and NOx from 1200 to 115 ppm.
Ammonia (NH3) emissions from gasoline-fueled vehicles have become an important source of pollution affecting urban air chemistry. NH3 influences the acidity of atmospheric depositions and it is involved in secondary aerosol formation. NH3 has to be considered as a secondary pollutant of the three-way-catalyst (TWC), since it is formed de novo during the DeNOx process. The extent of traffic-related hydrogen (H2) emissions and its impact on atmospheric redox chemistry is not well understood but is of increasing importance when we develop towards a hydrogen-based society. Herein we report on tail-pipe H2, NH3, and NO emissions of gasoline-fueled Euro-3 passenger cars at transient driving from 0 to 150 km h−1. The effects of velocity, acceleration, deceleration, and cold start were deduced from time-resolved EI- and CI-MS data. On a molar basis, H2 emissions were always higher than those of NH3 and NO by about an order of magnitude. H2 and NH3 emissions are correlated to some degree, as soon as catalyst light-off occurred. NH3 emissions exceeded those of NO for most vehicle conditions. Mean NH3/NO mixing ratios around two were observed with the exception of the cold start, where NO was present in large excess. Catalyst light-off is indicated by a fast transition from a NO- to a NH3-rich exhaust gas. All emissions clearly depend on speed and acceleration. Mean velocity-dependent emission factors varied by about one order of magnitude from 17 to 720, 8 to 170, and 7 to 80 mg km−1 for H2, NH3, and NO, respectively, with emission minima for all three pollutants when driving 70–90 km h−1. We conclude that the investigated Euro-3 vehicles are mainly operated under slightly reducing conditions, where NH3 and H2 emissions dominate over those of NO. Under these conditions, all vehicles fulfill the valid emission limit for NOx.
Vehicular emissions of reactive nitrogen compounds (RNCs) such as nitric oxide (NO), nitrogen dioxide (NO2), and ammonia (NH3) have a substantial impact on urban air quality. NO and NO2 support the photochemical formation of ozone, and NH3 is involved in the atmospheric formation of secondary aerosols. Vehicular NO is mainly formed during combustion, whereas NO2 and NH3 are both secondary pollutants of the catalytic converter systems. Herein we report on tail-pipe RNC emissions of gasoline-fueled Euro-3- and Euro-4-passenger cars at transient driving from 0 to 150 km h−1. Two sets of 10 in-use vehicles with comparable engine size and mileage were studied with time-resolved chemical ionization-mass spectrometry (CI-MS). Each vehicle was tested in 7 different driving cycles including the legislative European (EDC) and the US FTP-75 driving cycles. Mean emission factors (EFs) for different traffic situations are reported and effects of cold start, velocity, acceleration, and deceleration are discussed. Furthermore, critical operating conditions supporting the de novo formation of NH3 have been identified. In the EDC, mean NO- and NH3-EFs of 57±26 and 16±12 mg km−1 were obtained for Euro-3-vehicles; those of the Euro-4-technology were lower by about 25% and 33% at the levels of 43±46 and 10±7 mg km−1, respectively. NO2 emissions of the investigated three-way catalyst (TWC) vehicles accounted for <1% of the detected RNCs, whereas NH3 was found to be the dominant RNC for most vehicle conditions. Molar NH3 proportions varied from about 0.4–0.8, as soon as catalyst light-off occurred. NO was found in large excess only during the cold-start period. Catalyst light-off is indicated by a fast transition from NO- to NH3-rich exhaust. Velocity and acceleration had pronounced effects on the RNC emission characteristics. Mean velocity-dependent EFs for NO and NH3 varied by about one order of magnitude from 10 to 74 and 15 to 161 mg km−1 for Euro-3-vehicles and from 12 to 44 and 7 to 144 mg km−1 for the Euro-4 fleet. We conclude that the investigated Euro-3- and Euro-4-vehicles are mainly operated under slightly reducing conditions, where the NH3 emissions dominate over those of the NO. Under these conditions, both vehicle fleets on an average fulfilled the valid Euro-3 and Euro-4 limits for nitrogen oxides (NOx) of 150 and 80 mg km−1, respectively (as NO2 equivalents).
We used Fourier Transform Infrared Spectroscopy (FTIR) to measure tailpipe ammonia emissions from a representative fleet of 41 light and medium-duty vehicles recruited in the California South Coast Air Basin. A total of 121 chassis dynamometer emissions tests were conducted on these vehicles and the test results were examined to determine the effects of several key variables on ammonia emissions. Variables included vehicle type, driving cycle, emissions technology, ammonia precursor emissions (i.e. CO and NOx) and odometer readings/model year as a proxy for catalyst age. The mean ammonia emissions factor was 46 mg km−1 (σ = 48 mg km−1) for the vehicle fleet. Average emission factors for specific vehicle groups are also reported in this study. Results of this study suggest vehicles with the highest ammonia emission rates possess the following characteristics: medium-duty vehicles, older emissions technologies, mid-range odometer readings, and higher CO emissions. In addition, vehicles subjected to aggressive driving conditions are likely to be higher ammonia emitters. Since the vehicles we studied were representative of recent model year vehicles and technologies in urban airsheds, the results of our study will be useful for developing ammonia emissions inventories in Los Angeles and other urban areas where California-certified vehicles are driven. However, efforts should also be made to continue emissions testing on in-use vehicles to ensure greater confidence in the ammonia emission factors reported here.
Ammonia (NH3) is classified as a toxic air pollutant but its release from vehicles is not regulated. Herein we report on the efficiency of the catalytic reduction of nitrogen monoxide (NO) and the selectivity towards NH3. Chemical ionization mass spectrometry (CIMS) has been applied to monitor NH3 and NO emissions at a time resolution of 2 s. At real world driving, intense, catalyst-induced NH3 formation was detected for a gasoline-fueled passenger car equipped with a Pd/Rh-based three-way-catalyst (TWC). Post-catalyst NH3 emissions strongly depend on velocity and acceleration and varied by two orders of magnitude from 1 to 170 mg km−1. For most vehicle conditions, tail-pipe NH3 emissions exceeded those of NO. Excellent NO conversion above 95% was noticed as soon as catalyst light-off occurred. Post-catalyst NO emissions were lowest when NH3 formation was most intense and vice versa. This complementary behavior indicates that a TWC can be operated in a way that either NH3 or NO emissions dominate. The NH3/NO mixing ratio was mainly influenced by the air-to-fuel ratio. At fuel-rich combustion (λ<1), highest NH3/NO mixing ratios clearly above one were observed, whereas ratios at or below one were found at lean conditions (λ>1). Catalyst temperature effected the selectivity of the DeNOx process. Highest NH3 selectivity up to 0.45 was found when operating the catalyst below 280 °C. Above this temperature, the selectivity was reduced to 0.02–0.05. The obtained results highlight those parameters, influencing the NH3 output of a TWC vehicle at real world driving.
Emissions rates of ammonia (NH3) are reported for a fleet of 39 in-use light-duty gasoline-fueled vehicles. The fleet consisted of both light-duty passenger vehicles and light-duty trucks with various levels of emission control technologies, ranging from non-catalyst vehicles to those that were certified at the ULEV standard for California. NH3 measurements were performed using Fourier transform infrared spectroscopy and the federal test procedure (FTP) driving cycle. The FTP NH3 emission rate for this fleet of vehicles averaged 54 mg mi−1 with a range from <4 to 177 mg mi−1. For this fleet of vehicles, NH3 emissions did not decline as significantly as the regulated pollutants with improvements in emission control technology. A subset of 5 vehicles was tested over the US06, the New York City Cycle (NYCC), and a high-speed freeway cycle for comparison with the FTP cycle. NH3 emissions showed a strong cycle dependence, with increased emissions under more aggressive driving conditions. These results show that NH3 emissions formed during more aggressive driving conditions should be considered in the development of NH3 emission factors. The onset of NH3 emissions typically occurred after catalyst light-off, near when the catalyst reached its equilibrium temperature. Initial studies showed that NH3 emissions increased as the sulfur content in the fuel was decreased.
Motor vehicle emissions of ammonia have been measured at a California highway tunnel in the San Francisco Bay area. Between 1999 and 2006, light-duty vehicle ammonia emissions decreased by 38 ± 6%, from 640 ± 40 to 400 ± 20 mg kg−1. High time resolution measurements of ammonia made in summer 2001 at the same location indicate a minimum in ammonia emissions correlated with slower-speed driving conditions. Variations in ammonia emission rates track changes in carbon monoxide more closely than changes in nitrogen oxides, especially during later evening hours when traffic speeds are highest. Analysis of remote sensing data of Burgard et al. (Environmental Science Technology 2006, 40, 7018–22) indicates relationships between ammonia and vehicle model year, nitrogen oxides, and carbon monoxide. Ammonia emission rates from diesel trucks were difficult to measure in the tunnel setting due to the large contribution to ammonia concentrations in a mixed-traffic bore that were assigned to light-duty vehicle emissions. Nevertheless, it is clear that heavy-duty diesel trucks are a minor source of ammonia emissions compared to light-duty gasoline vehicles.
A comprehensive organic compound based receptor model is developed that can simultaneously apportion the source contributions to atmospheric gas phase organic compounds semivolatile organic compounds fine particle organic compounds and fine particle mass The model is applied to ambient data collected at four sites in the south coast region of California during a severe summertime photochemical smog episode where the model determines the direct primary contributions to atmospheric pollutants from 11 distinct air pollution source types The 11 sources included in the model are gasoline powered motor vehicle exhaust diesel engine exhaust whole gasoline vapors gasoline headspace vapors organic solvent vapors whole diesel fuel paved road dust tire wear debris meat cooking exhaust natural gas leakage and vegetative detritus Gasoline engine exhaust plus whole gasoline vapors are the predominant sources of volatile organic gases while gasoline and diesel engine exhaust plus diesel fuel vapors dominate the emissions of semivolable organic compounds from these sources during the episode studied at all four air monitoring sites The atmospheric fine particle organic compound mass was composed of noticeable contributions from gasoline powered motor vehicle exhaust diesel engine exhaust meat cooking and paved road dust with smaller but quantifiable contributions from vegetative detritus and tire wear debris In addition secondary organic aerosol which is formed from the low vapor pressure products of gas phase chemical reactions is found to be a major source of fine particle organic compound mass under the severe photochemical smog conditions studied here The concentrations of secondary organic aerosol calculated in the present study are compared with previous fine particle source apportionment results for less intense photochemical smog conditions.
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