Pt-Pd-based noble metal catalysts are widely used in engine exhaust aftertreatment because of their better carbon soot oxidation performance. At present, the synergistic effect of Pt and Pd in CDPFs, ...which is the most widely used and common doping method, in catalyzing the combustion of carbon smoke has not been reported, and it is not possible to give an optimal doping ratio of Pt and Pd. This paper investigates the carbon soot oxidation performance of different Pt/Pd ratios (Pt/Pd = 1:0, 10:1, 5:1, 1:1) based on physicochemical characterization and particle combustion kinetics calculations, aiming to reveal the Pt-Pd synergistic effect and its carbon soot oxidation law. The results show that Pt-based catalysts doped with Pd can improve the catalyst dispersion, significantly increase the specific surface area, and reduce the activation energy and reaction temperature of carbon soot reactions, but excessive doping of Pd leads to the enhancement of the catalyst agglomeration effect, a decrease in the specific surface area, and an increase in the activation energy and reaction temperature of the carbon soot reaction. The specific surface area and pore capacity of the catalyst are the largest, and the activation energy of particle oxidation and the pre-exponential factor are the smallest (203.44 kJ∙mol−1 and 6.31 × 107, respectively), which are 19.29 kJ∙mol−1 and 4.95 × 108 lower than those of pure carbon soot; meanwhile, the starting and final combustion temperatures of carbon soot (T10 and T90) are the lowest at 585.8 °C and 679.4 °C, respectively, which are 22.1 °C and 20.9 °C lower than those of pure carbon soot.
Different from vehicle engines, Diesel Particulate Filter (DPF) inactivation is an unavoidable issue for low-speed marine diesel engines fueled with Heavy Fuel Oil (HFO). This paper introduced a ...sulfur resisting material in Silicon Carbide (SiC)-DPF to improve DPF performance. The results of bench-scale experiments showed that the Balance Point Temperature of the modified DPF module was 300°C and DPF modules had a good filtration performance, with Particulate Matters (PMs) residual being less than 0.6 g per cycle. In pilot-scale tests, PMs emissions of unit power decreased with engine load going up, filtration efficiency of nucleation mode PMs being only 36% under 100% load, while DPF still had a good performance in accumulation mode PMs control, being 94.2% under the same load. DPF modules showed excellent regeneration durability in the 205h endurance test, with a regeneration period of 1.5-2h under 380°C. There was no obvious degeneration in the DPF module structure, with no cracks or breakage. Besides, the DPF module could also control gaseous emissions, total emissions decreased by 10.53% for NO and 57.19% for CO, respectively. The results suggested that introducing sulfur-resisting material in DPF could greatly improve the DPF performance of low-speed marine diesel engines fueled with HFO.
Shipping emissions have aroused wide concern in the world. In order to promote the implementation of emission regulations, this study develop a ship based sniffing technique to perform remote ...measurement of the SO.sub.2, NO.sub.x and CO.sub.2 from ships entering and leaving Shanghai port at the open sea. The ship emission prediction model, Smoke diffusion model and source identification model were developed to automatically analyze the emission data and screen the object ship source based on Automatic Identification System (AIS) system. The fueling documents of the detected ship were obtained from maritime sector and the results precision of the sniffer technique was evaluated by comparing the measured Fuel sulfur content (FSC) with actual value deduced from fueling documents. The influences of wind speed and direction, object ship parameters and monitoring distance on the identification of object ship and accuracy of the calculated FSC were thoroughly investigated and the corresponding correction factors under different conditions were deduced. The modified emission factor ratio of CO.sub.2 to NOx were proposed in order to improve the accuracy. It is demonstrated that with wind speed higher than 2 m/s and test distance shorter than 400m, the sniffer technique exhibit high efficiency and accuracy for the remote emissions measurement of ship upwind with detection rate higher than 90% and test error of FSC below 15%. To reduce the influence of the wind direction, at least two sniffer systems were required to guarantee that at least one station is in the downwind of the ship lane. Based on the results and discussion, a novel sniffer monitoring system with two buoy based sniffing stations placed close to each side of the ship lane far off shore was proposed to realize the remote monitoring of ship emissions.
The combination of diesel oxidation catalyst (DOC), catalyzed diesel particulate filter (CDPF) and selective catalytic reduction (SCR) is the most effective way to reduce particulate emission and ...nitrogen oxide (NOx) from diesel engines. In this study, the effects of a DOC+CDPF+SCR system on the emissions including carbon monoxide (CO) total hydrocarbon (THC), NOx, particle number (PN) and particle mass (PM) from a heavy-duty diesel engine were evaluated. In addition, the influences of ammonia (NH3) slip catalyst (ASC) coating and SCR catalyst downsizing on the NOx conversion efficiency, nitrous oxide (N2O) emissions and NH3 slip were also investigated. Results showed that the installation of the after-treatment system had negligible effect on the power and BSFC of the engine. The upstream DOC reduced by an average of 97.0% of the CO and 67.5% of the THC, in combination with CDPF, the CO and THC emission further decreased with an average drop of 97.8% and 72.5%, respectively. In terms of particulate emissions, the single DOC reduced 48.0% of the PN and 50.9% of the PM, and the combination of DOC and CDPF led to a reduction of 98.0% in the PN and 96.9% in the PM on average. The SCR was effective in reducing NOx emission, but resulted in higher N2O emission by more than 3 times, meanwhile led to an average NH3 slip of 3.80 ppm. Downsizing the SCR length by 1/3 could still ensure a 91.9% conversion efficiency of NOx, and produced less N2O, but led to an increase of the NH3 slip by 2 times, reaching 7.63 ppm on average. By coating Pt-based ASC catalyst on the back end of the SCR could eliminate the NH3 slip. Considering the cost and performance, the combination of DOC, CDPF and a downsized SCR with ASC coating may be a better choice.
This study involved conducting an experimental and numerical investigation on the effects of the air-to-fuel ratio (AFR), engine speed, and engine load on the inlet gas component of a three-way ...catalyst (TWC) and on the effects of noble metal loading, noble metal ratio, and carrier pore density on the emission conversion efficiency. The results showed that AFR can significantly affect the raw emissions of NOx and total hydrocarbon (THC), and better emission conversion efficiency of a TWC can be reached when AFR is controlled between 0.995 to 1. Compared with engine speed, engine load has a relatively small effect on exhaust temperature but greatly affects the flow velocity and NOx and THC emissions. Increasing the content of Pt in the catalyst can improve the THC conversion efficiency. For low Pt and Pd-Rh catalysts, the THC conversion effect is significantly deteriorated. The content of Rh affects the NOx conversion, and NOx conversion efficiency at high speeds is significantly reduced when Rh content is reduced. Higher carrier pore density can slightly improve the catalytic reaction rate and emission conversion efficiency at high engine speeds. However, high conversion efficiency can be maintained even after aging.
This
paper involved conducting an experimental investigation on the effects of exhaust
gas recirculation (EGR) and spark timing on the combustion, performance,
and emission characteristics of a ...China-VI heavy-duty, natural gas
engine fueled with high-methane content. The results showed that increasing
the EGR rate extends the spark timing range and slows the combustion.
This then increases ignition delay, prolongs combustion duration,
and decreases heat release rate. Peak in-cylinder pressure (PCP) and
indicated thermal efficiency (ITE) initially increase because of higher
boost pressure with increasing EGR rate. However, as EGR rate increases
further, PCP and ITE begin to decrease because of the deviation of
combustion phasing. Lower in-cylinder temperature caused by higher
EGR rate may cause nitrogen oxide (NOx) emissions to reduce significantly,
while total hydrocarbon (THC) and carbon monoxide (CO) emissions increase,
and THC emissions could increase exponentially at high EGR rates.
In-cylinder pressure, temperature, and heat release rate increase
with early spark timing, but the rate of increase is reduced at higher
engine speeds. Early spark timing causes THC and CO emissions to increase
at part-load conditions, whereas there is little change at full-load
conditions. NOx emissions also increase with early spark timing because
of the higher in-cylinder temperature.
On-road emission measurements of gasoline- and diesel-fueled vehicles were conducted by a portable emission measurement system (PEMS) in Shanghai, China. Horiba OBS 2200 and TSI EEPS 3090 were ...employed to detect gaseous and ultrafine particle emissions during the tests. The driving-based emission factors of gaseous pollutants and particle mass and number were obtained on various road types. The average NOx emission factors of the diesel bus, diesel car, and gasoline car were 8.86, 0.68, and 0.17 g km−1, all of which were in excess of their emission limits. The particle number emission factors were 7.06 × 1014, 6.08 × 1014, and 1.57 × 1014 km−1, generally higher than the results for similar vehicle types reported in the previous studies. The size distributions of the particles emitted from the diesel vehicles were mainly concentrated in the accumulation mode, while those emitted from the gasoline car were mainly distributed in the nucleation mode. Both gaseous and particle emission rates exhibit significant correlations with the change in vehicle speed and power demand. The lowest emission rates for each vehicle type were produced during idling. The highest emission rates for each vehicle type were generally found in high-VSP bins. The particle number emission rates of the gasoline car show the strongest growth trend with increasing VSP and speed. The particle number emission for the gasoline car increased by 3 orders of magnitude from idling to the highest VSP and driving speed conditions. High engine power caused by aggressive driving or heavy loads is the main contributor to high emissions for these vehicles in real-world situations.
•We measured gasoline- and diesel-fueled vehicles by a PEMS system.•The emission factors show strong relationship with real-world driving conditions.•Gasoline- and diesel-fueled vehicles show special size distributions.•Gasoline car emitted more nano-particles than diesel vehicles.•Particles show growth trends with the increase of VSP and speed in real-world.
This contribution is focused on the fuel economy improvement of the Miller cycle under part-load characteristics on a supercharged DI (Direct Injection) gasoline engine. Firstly, based on the engine ...bench test, the effects with the Miller cycle application under 3000 rpm were studied. The results show that the Miller cycle has different extents of improvement on pumping loss, combustion and friction loss. For low, medium and high loads, the brake thermal efficiency of the baseline engine is increased by 2.8%, 2.5% and 2.6%, respectively. Besides, the baseline variable valve timing (VVT) is optimized by the test. Subsequently, the 1D CFD (Computational Fluid Dynamics) model of the Miller cycle engine after the test optimization at the working condition of 3000 rpm and BMEP (Brake Mean Effective Pressure) = 10 bar was established, and the influence of the combined change of intake and exhaust valve timing on Miller cycle was studied by simulation. The results show that as the effect of the Miller cycle deepens, the engine’s knocking tendency decreases, so the ignition timing can be further advanced, and the economy of the engine can be improved. Compared with the brake thermal efficiency of the baseline engine, the final result after simulation optimization is increased from 34.6% to 35.6%, which is an improvement of 2.9%.
An insufficient amount of NH3 (ammonia) will reduce the conversion efficiency of NOx, which may lead to excess NOx emissions, resulting in NH3-SCR failure. In this article, SCR failure caused by a ...low NH3- NOx ratio is studied systematically by experiments. The main reasons for a low NH3-NOx ratio in SCR include insufficient urea injection, hydrothermal aging of catalysts and urea crystallization. It was found from an insufficient urea injection experiment that with the increase of NH3- NOx ratio, the NOx conversion efficiency of the SCR system increased, but the ammonia leakage also increased. The main influencing factors of NOx conversion efficiency are different under different NH3- NOx ratios. A flow reactor system was used in the catalyst hydrothermal aging experiment to investigate the effect of hydrothermal aging on catalyst activity. After a 24 h hydrothermal aging experiment at 800 °C, the NOx conversion efficiency of the copper-based zeolite catalysts decreased significantly at the boundary of medium and low temperature regions. And the NO2- NOx ratio in the mixture had a significant effect on the catalytic performance. Thermogravimetry coupled to Fourier transform infrared spectroscopy (TG-FTIR) was used to analyze the composition of urea deposits in a urea deposits analysis experiment. It was found that the main components of urea deposits were urea and isocyanic acid (HNCO). Preventing HNCO polymerization, especially the formation of CYA, can decrease the formation of urea deposits.
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•The influencing factors of NOX conversion efficiency changes with NH3-NOX ratios.•The NO2-NOX ratio has a significant effect on the catalytic performance.•Preventing HNCO polymerization can decrease the formation of urea deposits.
With increasingly stringent emission regulations, the cold start emissions have become more important than ever. Using a low compression ratio is a feasible way to improve a heavy-duty engine’s ...efficiency and emissions. However, cold start performance restricts the development of this technology, especially at high altitudes. In response, we conducted a study of the emissions of a heavy-duty low-compression-ratio diesel engine during start-up process at different altitudes. A plateau simulation system controlled the inlet and exhaust pressure to create altitude environments of 0 m, 1000 m, 2000 m, 3000 m, 3750 m and 4500 m. The gas, particulate and volatile organic compound (VOC) emissions were analyzed with speed and cycle during the start-up process. The results indicated that cold start performance and combustion characteristics became worse as altitudes increased. The gas and particulate emissions of carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbon (THC) and nitrous oxide (NOX) almost all increased as the engine speed and altitude increased, and was much higher than in idle conditions. The PN and PM emissions in each particle diameter also increased as the altitude increased, which was the same as the nucleation mode and the accumulation mode particles. VOC emissions were also measured, which increased during the start-up process as altitudes increased.
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