Three-way Catalytic Converter Research Articles

Hydrogen doping control method for gasoline engine acceleration transient air-fuel ratio

One of the primary contributors to automobile exhaust pollution is the significant deviation between the actual and theoretical air-fuel ratios during transient conditions, leading to a decrease in the conversion efficiency of three-way catalytic converters. Therefore, it becomes imperative to enhance fuel economy, reduce pollutant emissions, and improve the accuracy of transient control over air-fuel ratio (AFR) in order to mitigate automobile exhaust pollution. In this study, we propose a Linear Active Disturbance Rejection Control (LADRC) Hydrogen Doping Compensation Controller (HDC) to achieve precise control over the acceleration transient AFR of gasoline engines. By analyzing the dynamic effects of oil film and its impact on AFR, we establish a dynamic effect model for oil film and utilize hydrogen's exceptional auxiliary combustion characteristics as compensation for fuel loss. Comparative experimental results demonstrate that our proposed algorithm can rapidly regulate the AFR close to its ideal value under three different transient conditions while exhibiting superior anti-interference capability and effectively enhancing fuel economy.

Effect of ceria–silica-based synthesized catalyst in a CI engine exhaust system operating with plastic oil blend

This study investigates the impact of ceria–silica (Ce–Si)-based catalyst integrated in the catalytic converter (CC) on the compression ignition (CI) engine's exhaust manifold. The synthesis catalyst, Ce–Si was developed with the solvothermal method and aged for 4 h at 55°C. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, thermogravimetric analysis, energy dispersive X-ray spectroscopy and transmission electron microscopy analyses were carried out to conclude the synthesis of the catalyst. The catalyst performance of the CC was tested for the emission behavior of nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbon (HC) and smoke. A custom-built CC was installed on the test engine's exhaust manifold. The synthesis catalyst was installed in the engine exhaust route of the stationary single-cylinder diesel engine to conduct the study. To determine the effect of the synthesis catalyst on the exhaust manifold to test both diesel and DPB (B50) fuel with and without CC. Under maximum load conditions, the presence of CC reduced oxide of nitrogen and carbon monoxide emissions by 23% and 17%, respectively, compared to diesel. The synthesized aerogel catalyst has a low density and a high surface area relative to its volume. Ce–Si aerogel catalyst can be used to improve the conversion efficiency of nitric oxide (NO), unburned hydrocarbon and CO in the three-way CC.

Effect of different exhaust parameters on conversion efficiency enhancement of a Pd–Rh three-way catalytic converter for heavy-duty natural gas engines

In this work, the influence of exhaust parameters on the conversion performance of the Pd–Rh three-way catalytic converter (TWC) for heavy-duty natural gas engines is investigated by CFD simulation. A mathematical model adopting an empirical global reaction mechanism for the Pd–Rh TWC is established and validated. The results indicate that the increase of exhaust CO concentration is beneficial to remove the CH4 and NO emissions. As the exhaust CO concentration increases from 0.7 % (stoichiometric condition) to 1.3 % at 623K, the conversion efficiencies of CH4 and NO increase by 8.1 % and 41.8 %, respectively. In GRA, the most important influencing factor on the conversion efficiencies of CH4 and CO is the exhaust O2 concentration. For the NO conversion efficiency, the primary and secondary relationships of the three factors are exhaust CO concentration＞exhaust flow rate＞exhaust O2 concentration. The orthogonal experiment analysis indicates that Case 7 shows better total conversion performance (CH4: 97.6 %; CO: 100 %; NO: 62.2 %) than other cases. Compared with the stoichiometric condition at 623K, the conversion efficiencies of CH4 and NO are improved by 97.8 % and 3.8 %.

The Suitability of the Three-way Catalyst for Hydrogen Fuelled Engines

This experimental study investigates the palladium/rhodium based three-way catalytic converter (TWC) in a H2 - gasoline dual-fuel spark ignition (SI) engine under stoichiometric and lean conditions. The work focused on lean-burn engine operating conditions with the aim of reducing NOX emissions during the combustion process, where the TWC is not effective, while improving the thermal efficiency of the engine. Under these lean-burn engine conditions, the combustion promoting properties of H2 allowed for maintained engine combustion stability as determined by the COVimep values even up to ultra lean conditions (λ=2.0). It was found that by reducing the combustion temperature through the application of lean conditions, engine out NOX emissions could be reduced or even eliminated, while under these conditions the TWC was effective in reducing engine-out carbon-based gaseous emissions.

Nanometric Metal Overlayer Catalysts: Fundamental Aspects and Applications

Nanometric metal overlayer catalysts have been developed as novel catalyst structures with high three-way catalytic performance for practical applications. The metal overlayer is prepared via a dry process using pulsed arc plasma deposition, unlike wet coating processes for conventional powder catalysts containing nanoparticles. The key point to achieving high performance is the extremely high turnover frequencies for specific chemical reactions catalyzed by a large two-dimensional surface compared with metal nanoparticles. This overview study presents the preparation, structure, performance, reaction mechanism, and thermal stability of metal overlayer catalysts, focusing on rhodium (Rh) and catalytic conversion of nitric oxide (NO). Rh plays a pivotal role in the reduction of NO to N2 in automotive three-way catalytic converters. The potential benefit of the overlayer structure is the minimum loading of precious metal, such as Rh, which is limited and expensive.

Key design and layout factors influencing performance of three-way catalytic converters: Experimental and semidecoupled numerical study under real-life driving conditions

The optimization of three-way catalyst (TWC) design and layout is important for reducing mobile source emissions and requires numerical modeling. To date, the high computational cost of accurate models has inspired the development of numerous tradeoff approaches; however, none of them is fully satisfactory. To address this gap, we herein theoretically and experimentally explore the key design and layout factors influencing TWC performance under transient driving conditions, starting with the optimization and verification of a simplified reaction mechanism. This mechanism is used to construct a semidecoupled posttreatment GT-Power model featuring boundary conditions derived from experimental and upstream engine modeling results, and experiments on a real engine are carried out to evaluate the model accuracy. The performance of three posttreatment systems is analyzed to identify the key performance-affecting parameters, and the following conclusions are drawn. (1) For a single reactor, cell density is the most important factor influencing pressure loss.(2) The exhaust temperature rapidly decreases in the longitudinal direction of the reactor in the initial start stage, although the reaction rate always decreases in this direction during the whole cycle.(3) One-dimensional plug-flow reactor simulations do not account for inhomogeneity and local turbulence, thus overestimating the performance of large reactors.(4) Under the employed conditions, the exhaust temperature is sufficiently high for pollutant conversion, although the efficiency of this conversion often decreases in the high-speed stage. Moreover, we show that high-speed adaptation can be enhanced by increasing the crosswise size of the reactor and propose a new reactor structure. Compared with our model, this structure is characterized by a lower catalyst loading and NOx conversion efficiency but achieves higher hydrocarbon and CO conversion efficiencies. Thus, our study provides a useful and effective method for evaluating the design/layout of posttreatment devices and facilitates the development of more efficient TWCs, contributing to the establishment of a more ecofriendly society.

Effects of chamber geometry, hydrogen ratio and EGR ratio on the combustion process and knocking characters of a HCNG engine at the stoichiometric condition

Stoichiometric operation natural gas engine can achieve low emissions and high-power output by combining EGR and three-way catalytic converter. However, under high load conditions, engine performance will be deteriorated due to the knocking limits. The main methods to solve the knocking problems of spark ignition engines are shortening the flame propagation time and reducing the temperature and pressure rise of the end mixture. This paper firstly established a 3D model based on a natural gas engine, and then conducted the numerical simulations to investigate the effects of chamber geometry, hydrogen ratio and EGR ratio on engine knocking and combustion. The validation indicates a satisfied numerical results of chamber pressure and heat release rate. The turbine chamber exhibits relatively better swirl and tumble, thus achieving the highest turbulence intensity. HCNG fuel will increase the knocking tendency of the engine. In the meantime, the addition of hydrogen will also reduce the IMEP of the engine due to the low volume heat value of hydrogen. However, the addition of hydrogen may accelerate the combustion rate at the end of combustion to a certain extent. EGR can significantly reduce the knocking tendency of HCNG engine by reducing the combustion temperature in the cylinder. Compared with the case of 14% EGR rate, the ignition angle of 30% EGR case is advanced by 19 °CA, and the indicated thermal efficiency is increased by 2.06%.

Determination of Vehicle Emission Rates for Ammonia and Organic Molecular Markers Using a Chassis Dynamometer

Stringent regulations have been implemented to address vehicle exhaust emissions and mitigate air pollution. However, the introduction of exhaust gas reduction devices, such as Three-Way Catalytic converters, has raised concerns about the generation and release of additional pollutants such as NH3. This study utilized a chassis dynamometer to investigate the characteristics of exhaust pollutants, including carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), particulate matter (PM), ammonia (NH3), organic carbon (OC), and elemental carbon (EC). The emissions were examined across various vehicle fuel types, namely liquefied petroleum gas, gasoline, and diesel (EURO4, EURO6), to assess their individual contributions to exhaust emissions. The results revealed significant variations in the emission levels of regulated pollutants (CO, HC, NOx, and PM) during driving, depending on factors such as engine technology, emissions control strategies, fuel type, and test cycle. Notably, NH3 emissions analysis according to driving mode indicated that gasoline vehicles exhibited the highest NH3 emissions, while diesel vehicles emitted negligible amounts. This observation can be attributed to the production of NH3 as a byproduct of catalytic reduction processes implemented by exhaust gas reduction devices targeting CO, HC, and NOx. In addition, EURO4 vehicles demonstrated higher emission levels of OC and EC compared with other fuel types. Furthermore, the presence of diesel particulate filters (DPFs) in diesel vehicles effectively reduced PM emissions. Moreover, this study investigated the emission characteristics of organic molecular markers within the organic carbon fraction, revealing distinct emission profiles for each vehicle and fuel type. These findings contribute to the identification of emission sources by discerning the primary components emitted by specific fuel types.

Multi-objective optimization of the three-way catalytic converter on the combustion and emission characteristics for a gasoline engine

Multi-objective optimization of the three-way catalytic converter on the combustion and emission characteristics for a gasoline engine

Exhaust aftertreatment device-derived ammonia emissions from conventional and hybrid light-duty gasoline vehicles over different driving cycles

Ammonia emissions from motor vehicles have great effect on air pollution and human health in urban areas. Recently, many countries have focus on ammonia emission measurement and control technologies for light-duty gasoline vehicles (LDGVs). To analyze ammonia emission characteristics, three conventional LDGVs and one hybrid electric light-duty vehicle (HEV) were evaluated over different driving cycles. The average ammonia emission factor at 23℃ was 4.5 ± 1.6 mg/km over Worldwide harmonized light vehicles test cycle (WLTC). Most ammonia emissions mainly concentrated in low and medium speed sections at cold-start stage, which were related to rich burn conditions. The increasing ambient temperatures led to the decrease of ammonia emissions, but high load caused by extremely elevated ambient temperature led to obvious ammonia emissions. The ammonia formation is also related to three-way catalytic converter (TWC) temperatures, and underfloor TWC catalyst could eliminate ammonia partly. The ammonia emission from HEV, which are significant less than LDGV, corresponded to the engine working state. The large temperature difference in the catalysts caused by power source shifts were the main reason. Exploring the effects of various factors on the ammonia emission is beneficial for revealing the instinct formation conditions, providing theoretical support for the future regulations.

Experimental and simulation study on Fe-beta controlling of hydrocarbon emission during cold start of gasoline vehicle world light vehicle test cycle

In order to address the extremely severe HC emissions during cold start of gasoline vehicles, a new HC trapping device was designed that can be installed in the aftertreatment system of the experimental gasoline vehicle in this study. This device has the same carrier as universal three-way catalytic converters (TWC), similar structure, and the HC trapping material was coated on the carrier of this device, the coating material used in this study was a new coating material, namely Fe-beta zeolite molecular sieve. Both vehicle experiments and molecular dynamics simulations were used in this study. The cold start experiments were carried out on the gasoline vehicle World Light Vehicle Test Cycle (WLTC). The experiments compared the differences in HC emissions from the exhaust gas of the gasoline vehicle with and without the HC trapping device. The experimental results showed that the installation of the HC trapping device significantly reduced HC emissions during the first 8 s of cold start, which was the worst phase of exhaust emissions from the gasoline vehicle. The peak value that occurred during this period was approximately tens of times greater than the peak value that occurred at later stages when HC emissions fluctuate. And the use of HC catcher resulted in a 62.34% reduction in the maximum peak value HC emissions. Then the molecular dynamics software Material studio was used to simulate the adsorption and diffusion of representative alkene molecules (butene, propene and ethene which measured from cold start test of experimental gasoline vehicle) on Fe-beta zeolite molecular sieves. The results showed that the adsorption effect was significant at low temperatures and the diffusion phenomenon was significant at high temperatures. When simulating the adsorption and diffusion of multi-component alkene molecules, there was a competitive relationship between various alkene molecules, which was greatly affected by the size of alkenes themselves. Ranking of the capture efficiency of three types of alkenes: butene > propene > ethene.

Design of effective catalysts for the aftertreatment of CNG-fueled vehicle exhaust by doping 1% Pt/Ce0.4Zr0.5La0.05Y0.05-xO1.95+x with niobium

With the improvement of current global vehicle emission standards increase and widespread application of natural gas vehicles (CNG), existing three-way catalytic converters (TWCs) need to be modified to meet the new emission regulations. In recent years, the price of palladium has been rising, while platinum, which is also used in catalytic systems, is relatively cheap, and the industry has come up with the idea of replacing palladium with platinum. Palladium loaded with a mass fraction of 1% on Ce0.4Zr0.5La0.05Y0.05O1.95 (CZLY) did show excellent catalytic activity, however, when palladium is replaced by platinum, the catalytic activity of the catalyst for methane combustion is significantly reduced. At 680 °C under oxygen-rich conditions (20%), methane conversion can typically reach 90%. The reduced 1% Pt/CZLY catalyst, on the other hand, was unstable in activity at high temperatures, although it was significantly higher at the starting temperature (T50 = 378 °C).In this work, it was found that the addition of niobium to CZLY improved the activity of Pt-based catalysts. The 1% Pt/Ce0.4Zr0.5La0.05Nb0.05O2 (1% Pt/CZLN) catalysts showed a decrease in T90 (CO) of 26 °C and T90 (CH4) of approximately 250 °C. The activity of this catalyst is consistent with that of the reduction pre-treatment 1% Pt/CZLY catalyst. Results from thermal deactivation and sulphur poisoning experiments show that the 1% Pt/CZLN catalyst exhibits superior thermal stability and anti-sulphur toxicity. For example, methane conversion of the 1% Pt/CZLN catalyst maintained at 85% at 600 °C for 32 h with a 5% decrease in activity.To clearly explain the effect of niobium doping on the catalyst, BET, XRD, H2-TPR, XPS and TEM tests were performed on the catalysts confirming that the strong Pt-Nb interaction stabilizes the valence state of the platinum and loads the platinum on the carrier surface in the active metallic platinum state. The amount of niobium doping was positively correlated with the metallic Pt content in the catalyst. In conclusion, the addition of niobium to platinum-based catalysts increases the methane combustion activity of the catalyst and delays thermal deactivation and sulphur poisoning of the platinum-based catalyst, extending the service life of the platinum-based catalyst.

Analysis of Unregulated VOCs Downstream a Three-Way Catalyst in a Simulated Gasoline Engine Exhaust under Non-Optimum Conditions

Urban air pollution is partly due to exhaust emissions from road transport. Vehicle emissions have been regulated for more than 30 years in many countries around the world. Each motor type is equipped with a specific emission control system. In gasoline vehicles, a three-way catalytic converter (TWC) is implemented to remove at the same time hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). However, TWCs are only efficient above 200 °C and at a stoichiometric air-to-fuel ratio in the exhaust. However, deviations from stoichiometry occur during fast accelerations and decelerations. This study reports the analysis of unregulated VOCs commercial mini-TWC fed by model gasoline gas mixtures. A synthetic gas bench was used to control the model exhaust containing two model hydrocarbons (propene and propane) to identify the conditions at which VOCs are created under non-optimal conditions. Most of the pollutants such as N2O and VOCs were emitted between 220 and 500 °C with a peak at around 280 °C, temperature which corresponds to the tipping point of the TWC activity. The combination of different mass spectrometric analysis (online and offline) allowed to identify many different VOCs: carbonated (acetone, acetaldehyde, acroleine), nitrile (acetonitrile, propanenitrile, acrylonitrile, cyanopropene) and aromatic (benzene, toluene) compounds. Growth mechanisms from propene and to a lesser extend propane are responsible for the formation of these higher aromatic compounds that could lead to the formation of secondary organic aerosol in a near-field area.

Preparation Method of Coating Material, Coating Material, Catalyst and Three-way Catalytic Converter

Preparation Method of Coating Material, Coating Material, Catalyst and Three-way Catalytic Converter

Fine structural characterization of noble metals in washcoat of motorcycle three-way converter catalysts

In Taiwan, over 14 million motorcycles exhaust vast amounts of pollutant gases, for which 24% of the total air pollutants cause significant air pollution in urban areas. The fine structures and the oxidation states of Pt/Pd/Rh/Ce species in washcoat catalysts of three-way motorcycle catalytic converters were investigated using EXAFS/XANES spectroscopy. Herein, a test of the federal test procedure (FTP) cycle for the deactivation of a motorcycle catalytic converter was conducted at running distances of 0, 5,000, 10,000, 15,000, and 30,000 km. Emissions of HCs pollutants were well controlled with Pt/Rh/Pd/Ce species supports on ceria/alumina washcoat owing to the exclusion of CO. The oxygen-rich environment leads to readily oxidized Rh and Pd species in the washcoat, while the Pt species are relatively difficult to oxidize. The Pd (Rh and Pt) species in the fresh and used washcoat catalysts have bond distances of 2.02 (2.03 and 1.90) and 2.75 (2.68 and 2.76) ± 0.02 Å and coordination numbers of 3.32 (5.70 and 4.13) and 11.81 (11.94 and 12.05) ± 0.05, respectively. Ceria species in washcoat catalysts are associated with the promotion of the crystalline phase to Ce(III) with a bond distance of 2.61 Å and a coordination number of 10.18 after 15,000 km catalyst FTP cycling. In addition, the transition metal is satisfactorily consisted with the La-O distances at about 2.49 Å.

Color-tunable, time-dependent, temperature and humidity-responsive afterglow from hyaluronic acid-based films

Pure organic afterglow materials with color-tunable and multiple stimuli-responsive afterglow are attractive but extremely scarce. Herein, a convenient strategy is reported to construct a series of hyaluronic acid (HA) -based afterglow films with color-tunable (from cyan to red) and multiple stimuli-responsive afterglow emissions (τafterglow, up to 971.05 ms). Disruption of hydrogen bonds and quenching of triplet excitons induced humidity-responsive afterglow, while time-dependent afterglow originates from diverse emissive species with different lifetimes. Moreover, due to the existence of dual-mode afterglow, the HA-based afterglow film doped with 9-aminophenanthrene (Aphe@HA) is endowed with temperature-responsive afterglow, and the Commission Internationale de l'Eclairage (CIE) coordinates of its colors could be linearly adjusted among yellow, white and blue from 298 K to 443 K. Considering the distinctive temperature-responsive afterglow, Aphe@HA can act as a temperature sensor in three-way catalytic converters (TWCs) and curling tongs. In addition, the color-tunable and humidity-responsive afterglow emissions of the HA-based films facilitate their applications in anti-counterfeiting and information encryption.

Surface State Changes of Pd Three-Way Catalysts under Dynamic Lean/Rich Perturbation Compared with Static Condition

In three-way catalytic converters, momentary perturbations of the exhaust gas composition between fuel-rich (reducing) and fuel-lean (oxidizing) conditions near the stoichiometric point affect the catalyst surface and the conversion efficiencies of NOx, CO, and hydrocarbons. However, the specific changes in the surface state of the catalyst under such dynamic conditions have not been elucidated in detail. In this study, in situ diffuse reflectance spectroscopy (DRS) was applied to monitor real-time changes in the surface state of Pd-based catalysts occurring under rich/lean perturbation at intervals of 2 s. The Pd oxidation state was found to fluctuate in synchronism with this perturbation, but its oscillation amplitude was much smaller when supported on CeO2–ZrO2 (CZ) than on Al2O3. Because this buffering effect of CZ due to its oxygen scavenging function mitigates the gradual oxidation of active metallic Pd to less-active Pd oxide, higher reaction rates were achieved especially for NOx and CO under the dynamic perturbation atmosphere. Furthermore, the Pd–CZ interface quickly supplied active oxygen species to prevent coke deposition originating from the decomposition of adsorbed hydrocarbon, which was unavoidable on Pd/Al2O3 under stoichiometric and fuel-rich conditions. This study demonstrates that in situ DRS provides a simple and useful tool for the direct observation of surface state changes under the real reaction atmosphere at the laboratory level. The information obtained is of great use for understanding the role of CZ in transient and unsteady-state catalytic processes and bridging a gap between real on-board TWC performances and laboratory tests.

Three-way catalyst modeling and fuel switch optimization of a natural gas bi-fuel-powered vehicle

In contemporary societies, improving engine efficiency and emission are critical targets for engine designers due to the increasing overwhelming popularity of electric powertrains. Compressed natural gas (CNG) is one of the alternatives for traditional fuels. Due to considerable HC emission during vehicle’s cold-start, the vehicle is started with gasoline and is switched to CNG fuel after a while. The optimum fuel switching time and its effect on total tailpipe emissions have not been addressed in the literature. Therefore, this study focuses on the detailed kinetic modeling of a three-way catalytic converter of a bi-fuel (gasoline/CNG) powered vehicle. The simulated results are validated with experimental data of the new European driving cycle (NEDC) emissions test. The pre-exponential factor (A), the energy of activation (E), and the exponent of temperature (β) for the 22 reactions of the three-way catalytic converter are calibrated by optimization. A genetic algorithm is implemented to optimize the reaction coefficients in both CNG and gasoline fuel mode. The validated model is also used to optimize the vehicle's tailpipe emissions in CNG operation conditions. The results reveal that NOx catalyst conversion efficiency is acceptable in highway driving conditions for CNG mode, while the CO conversion efficiency is inappropriate under the same conditions. It is found that THC catalyst efficiency in gasoline is better than CNG mode after cold-start due to the low reactivity of methane. Most gasoline tailpipe emissions are emitted during the cold-start, while CNG tailpipe emissions gradually increase after the cold-start. The fuel switch time from gasoline to CNG is optimized to 48 s after the vehicle start. While the NOx emission decreases by 15% at the end of the driving cycle, THC is not changed after optimization. The only THC reduction optimization goal leads to a switch time increase to 149 s after the start of driving.

Study on the effect of hydrocarbon structure on the reactivity of the three-way catalytic converter

The effect of hydrocarbon structures on reduction of nitric oxide and oxidation of carbon monoxide and hydrocarbons on the palladium-rhodium catalyst supported on aluminum-cerium-zirconium oxide was examined with fixed-bed flow reactor using synthetic gas. As regards olefinic hydrocarbons, the lower the number of carbon atoms, the higher the rate of reduction of nitric oxide, the lower the number of carbon atoms, the greater the rate of oxidation of hydrocarbons and carbon monoxide. Olefinic hydrocarbons have a π bond and are highly adsorbed on catalytic sites. Consequently, it may be hypothesized that if the number of carbon atoms increases, the adsorption ability becomes too high and the reactivity of the hydrocarbons decreases. On the other hand, for paraffinic hydrocarbons, the greater the number of carbon atoms, the greater the rate of reduction of nitric oxide, and the more carbon atoms there are, the higher the oxidation rate of the hydrocarbon. In the case of paraffinic hydrocarbons, there are only σ bonds and less adsorption on the catalyst site, it is therefore assumed that the greater the number of carbon atoms, the greater the reactivity of the hydrocarbon. The results of the effects of these hydrocarbon structures on the overall three-way catalytic reaction activity provide an indicator of the development of new catalysts.

Effects of fuel injection system and exhaust gas catalytic treatments on PAH emissions from motorcycles.

The motorcycles are unignorable near-ground pollutant emission sources that increase the human exposure in the dense area. However, the information of the polycyclic aromatic hydrocarbons (PAHs) emissions under different scenarios of engine and emission control for motorcycle is limited. This study focused on the PAH emissions from two fuel-injection types of motorcycles, including the premixed fuel-injection (PFi) with carburetor and electronic fuel-injection (EFi). Specifically, the effects of throttle opening (TO), secondary air system (SAS), oxygen sensor (OS), oxidation catalytic converter (OCC), and three-way catalytic converter (TWC) on PAH emissions are investigated. Results show that the PAH emission concentrations increase 227-727%, 351-492%, and 155-408% by the increasing TO ratio, unworking SAS, and OS units in both motorcycles. For the PFi engine, the OCC unit is found to be more effective in PAH control (31-89%) than the SAS system (72-80%), especially under low TO operation. For the EFi engine which dominates the motorcycle market recently, the oxygen sensor for more accurate combustion control shows a better PAH reduction (36-76%) than TWC system (21-66%). The ultra-fine particulate phase PAHs, which is hardly removed by catalyst, needs to be further considered. Moreover, the total PAH emission level of the EFi engine is still about ten times higher than that of the PFi. By the annual emission calculation for three densely populated countries, the recent evolution significantly reduces the annual hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions but have unignorable PAH emissions. These emissions continuously affect the human health in the near-ground urban air and need to be considered in the next generation of motorcycle design.