Abstract
Due to the inherent combustion characteristics of diesel engines, particulate matter (PM) and nitrogen oxides (NOx) are the main pollutants of diesel engines. NOx emissions under low load and low temperature are the focus of future regulation. Selective catalytic reduction coated on diesel particulate filter (SDPF) can reduce NOx and PM emissions of diesel engines at the same time, especially improving the emission characteristics of NOx under low load and low temperature. In this paper, a light-duty diesel engine with diesel oxidation catalyst (DOC) and SDPF was studied, and emission of particulate and gaseous pollutants of the engine before DOC, after DOC, and after SDPF was measured under 10 steady-state operating conditions. The effects of SDPF on particulate size distribution, the filtration efficiency of particulate, and the conversion efficiency of gaseous pollutants were analyzed. The results show that DOC + SDPF can trap PM with particle sizes between 10 and 23 nm by 1–2 orders of magnitude, and the conversion and filtration efficiency of DOC + SDPF for both gaseous pollutants and PM exceeds 90% under low-temperature and low-load conditions. The filtration efficiency of SDPF is 94.37% for PM and 90.36% for PN, and the conversion efficiency is 91.43% for NOx.
1. Introduction
Diesel engines are the main power source of commercial vehicles at present because of their power and economic advantages. Due to its inherent combustion characteristics, particulate matter (PM) and nitrogen oxides (NOx) are the main pollutants of the diesel engine emissions. Worldwide, emission regulation of diesel engines is becoming more and more strict. These pollutants not only pollute the environment but also endanger people’s health.1−4
At present, diesel particulate filter (DPF) technology, selective catalytic reduction (SCR) technology, and diesel oxidation catalyst (DOC) technology are mainly used to deal with the emission of diesel engines. These technologies have their own use in dealing with different pollutants.5−8 DPF technology is a more mainstream diesel particulate aftertreatment technology at this stage. Its core component is the internal filter element, mainly including a wire mesh filter, a ceramic fiber filter, a wall flow ceramic filter, and a foam ceramic filter.9,10 At present, the commonly used filter element is the ceramic filter, which has long service life, low price, and better performance.11 SCR technology is currently the most efficient method to treat NOx. It generates nitrogen and water from NOx and some hydrocarbons in the tail gas through reduction reaction so as to achieve the purpose of reducing emissions of pollutants.12 DOC technology is mainly used to eliminate soluble organic fraction (SOF) in particles to reduce the emission of particles and can reduce HC and CO in the emission gas at the same time.13
Due to the increasingly strict regulation, the engine has done a lot of research and development work in the in-cylinder combustion stage so as to achieve the purpose of reducing pollutant emissions. However, as we all know, these combustion technologies cost too much, and the technology is not mature enough to adapt to large-scale market applications.14 In addition, the pollutants produced by diesel engines are diverse, and it is difficult to deal with all of the pollutants emitted by a single technology. Therefore, it is necessary to develop an efficient DOC + SDPF system.
DPF coated with SCR (SDPF) is an aftertreatment technology for diesel engine emissions, in which the SCR catalyst is coated in the porous media filter wall of DPF, which can reduce the emissions of NOx and particulates at the same time. SDPF technology is widely used in dealing with the conversion of NOx under low-temperature and low-load conditions. At present, the aftertreatment technology route of DOC + SDPF + ammonia slip catalyst (ASC) is generally adopted. It has the advantages of a shorter preheating time, a lower heat capacity loss, and a higher reaction temperature.15,16 At present, there are many studies on its treatment of gaseous oxides in the world, but there is little research and analysis on its ability to filter particulates. In fact, SDPF technology also has significant efficiency in filtering particulates.
In some papers, scholars have studied the influence of SDPF on engine emissions under different conditions, including the catalyst coating rate, coating amount, and catalyst support structure. Because the space velocity of wall flow in SDPF increases, its NOx conversion rate will be lower than that of full flow in SCR. Therefore, to increase the NOx conversion rate in SPDF, it is necessary to coat a catalyst much larger than SCR; this will also lead to the decrease of the porosity and permeability of the filter wall, increase the back pressure of SDPF, and reduce the fuel economy.17,18
Taylor et al.19 found that uniform coating helps to reduce the back pressure, but the pressure drop is still 12% higher than that of DPF with the same coating amount. The position of catalyst coating will also affect the back pressure and NOx conversion of SDPF. Rappé et al.20,21 believe that the internal coating of the wall has a higher utilization rate of the SCR catalyst than the surface coating of the wall and is conducive to reducing the resistance of exhaust flow and improving PM storage. Ballinger et al.22 found that reducing the coating amount of the SCR catalyst by 25% will reduce NOx conversion by 6%, but the back pressure will be reduced by 35%. Karamitros and Koltsakis23 studied the effect of partition coating of the SCR catalyst on the performance of SDPF based on the model, indicating that partition coating will change the wall flow distribution. The selection of the SDPF catalyst needs to consider achieving high NOx conversion at high and low temperatures at the same time as well as good thermal stability and preventing thermal aging under high-temperature conditions of active regeneration. At present, the two most widely used types of SCR catalysts are vanadium-based and zeolite-based catalysts, and the most widely used in SDPF is the coated zeolite-based SCR catalyst.20 To optimize the performance of SDPF, researchers have developed a new type of Cu/lta (Linde type A) catalyst and selective catalyst oxidation (SCO). Mohan et al.24 summarized and compared the NOx conversion performance of cu/ssz-13, cu/sapo-34, and cu/ZSM-5. Among them, cu/ssz-13 has the widest reaction temperature window; that is, it has good NOx conversion performance at a wide range of temperatures. The Cu/ssz-13 catalyst has been widely used in SDPF because of its good NOx conversion performance and thermal stability.25−28
Many studies have proved that DOC and SDPF have great potential in reducing engine pollution emissions and can already meet the actual emission regulatory requirements. However, there is still a huge gap in the actual road conditions and combined applications, and there is a lack of research on the emission test of the engine under different working conditions. In addition, the emission control of diesel engines should meet the economy and operability at the same time, so the aftertreatment equipment is required to be as simple as possible, the filtration and conversion efficiency is as high as possible, and the cost of the equipment is as low as possible. For the design of the SDPF substrate, aluminum titanate (AT) could be selected because AT has an optimized microstructure and high porosity, and it still has a low back pressure under a higher load with the SCR catalyst, good heat resistance, and high carbon load limit.29 Chen pointed out that the fuel consumption rate of the engine is independent of the soot load. However, the rise of the soot load will make the pressure drop and the inlet temperature of SDPF both increase and will also cause a sharp decline in NOx conversion efficiency. NOx conversion efficiency is affected by exhaust temperature and NO2 concentration. When the soot load is 9.97 g/L, SDPF cannot effectively reduce NOx emission. The particulate number (PN) emission of the nucleation mode could decrease with SDPF by 2–3 orders of magnitude. The filtration efficiency of PN emission from the nucleation mode is affected by both the physical collection mechanism and chemical reaction. SDPF can reduce PN emission in the accumulation mode by 1–2 orders of magnitude. The increase of the dust load of SDPF can effectively reduce the PN emission in the denuclearization mode but has no obvious impact on the PN emission in the accumulation mode. Under low speed conditions, the increase of carbon load of SDPF will significantly improve the filtration efficiency of PN in nucleation mode and accumulation mode. The maximum filtration efficiencies of the nucleation mode, accumulation mode, and total PN are 99.93, 99.36, and 99.56%, respectively. With the rise of soot load, the geometric average diameter of SDPF increases.30 With the promulgation of the latest laws and regulations, the requirements for emissions have been further improved. Therefore, it is very necessary to design a set of aftertreatment systems that meet the emission regulations and promote the development of diesel engine emissions.
This paper takes a light-duty diesel engine as the object and studies its pollutant emission characteristics after equipping DOC and SDPF. The emission characteristics of particulate and gaseous pollutants before DOC, after DOC, and after SDPF were measured at 10 steady-state operating points on the engine bench. The purification ability of the DOC + SDPF system for pollution emissions under different operating conditions was studied, and the relationship between particulate size distribution and SDPF was analyzed. The actual conversion efficiency of gaseous pollutants and the actual filtration efficiency of particulate were also analyzed. Finally, a practical solution that meets the stringent emission regulations and can be applied to diesel vehicles is proposed, which has outstanding value and significance in diesel vehicle emission control.
2. Materials and Methods
2.1. Experimental System
The test subject is a light-duty diesel engine, as shown in Figure1, and the specific parameters are presented in Table 1.
Figure 1.
Test engine.
Table 1. Test Diesel Engine Experiment Parameters.
| engine index | technical parameter |
|---|---|
| engine type | inline four, turbocharge intercooling |
| cylinder bore × stroke | 94 mm ×100 mm |
| displacement | 2.776 L |
| rated power/speed | 105 kW/3000 rpm |
| rated torque/speed | 360 N·m/1600–2400 rpm |
| idle speed | 750 rpm |
| compression ratio | 17.1:1 |
The basic engine test equipment includes an engine measurement and control system, an electric dynamometer, an air flowmeter, and an engine instantaneous fuel consumption meter. Locally available commercial diesel fuel with a sulfur content of 1 ppm, as shown in Table 2, is used as the fuel for the engine.
Table 2. Fuel Properties of Diesel.
| parameter | value |
|---|---|
| cetane number | 52.3 |
| density, 20 °C (kg/m3) | 821.9 |
| viscosity, 20 °C (mm2/s) | 4.54 |
| low calorific value (MJ/kg) | 43.96 |
| T90 (°C) | 325 |
| carbon (%, m/m) | 86.12 |
| hydrogen (%, m/m) | 13.84 |
| oxygen (%, m/m) | 0 |
| sulfur (ppm, m/m) | 1.2 |
The emission test equipment is a Horiba mexa-1600dsegr engine exhaust analyzer, a TSI EEPS-3090 particulate size analyzer, an armored thermocouple kx391a, and a PTX 5072-tb-a3-ca-h0-pa pressure sensor. The details are listed in Table 3.
Table 3. Emission Test Equipment Informationa.
| number | equipment name | tested components | range | accuracy |
|---|---|---|---|---|
| 1 | engine exhaust analyzer | CO, CO2, THC, NOx, O2 | CO, 0–3000 ppmC; CO2, 0–16%; THC, 0–20000 ppmC; NOx, 0–5000 ppm; O2, 0–20% | ±1.0% FS |
| 2 | particulate size analyzer | PM | 5.6–560 nm, 0–1 × 108 #/cm3 | / |
| 3 | thermocouple KX391A | / | –40–1100 °C | ±1.5 °C |
| 4 | pressure sensor | / | –50–100 kPa | ±0.05 kPa |
The solidus (/) in number 2 means that the manufacturer does not provide this parameter. The solidus (/) in numbers 3 and 4 represent not measuring the actual substance but measuring some property.
The schematic of engine bench is shown in Figure 2.
Figure 2.
Schematic of engine bench.
2.2. Property of the DOC and SDPF
DOC and SDPF catalysts constitute the aftertreatment system. The DOC substrate is coated with precious metal platinum/palladium (3:1) with a diameter–length ratio of 147 mm × 110 mm and a volume of 1.866 L. The SDPF substrate has a volume of 4.4 L, and the main material is Cu/SSZ-13. Table 4 (Line 151) shows the specifications of DOC and the SDPF.
Table 4. Specifications of the DOC and the SDPF.
| parameter | DOC | SDPF |
|---|---|---|
| main material | Fe/Cr/Al | aluminum titanate |
| type | full flow | wall flow |
| cell’s density (cell/in.2) | 400 | 350 |
| wall thickness (mil) | 2.4 | 12 |
| diameter × length (mm × mm) | 147 × 110 | 177.8 × 177.8 |
| porosity (%) | /a | 65 |
| catalyst | Pt/Pd (3:1) | Cu/SSZ-13 |
| catalyst loading (g/L) | 2 | 120 |
The solidus (/) indicates that DOC does not have porosity.
2.3. Experimental Scheme
First, the fuel consumption, exhaust temperature, torque, and pressure of the engine were tested on the bench. The DOC + SDPF system is equipped in the exhaust section of the engine, and three test points are set to collect data of gaseous pollutants, PM, temperature, and pressure, which is shown in Figure 3.
Figure 3.
Schematic diagram of acquisition measuring points.
For the test engine, the following 10 operating conditions are set for testing. Under the working condition of 75% load, the speed of diesel engine is set to 1000, 1300, 1600, 1900, and 2200 rpm, respectively. The load rate of the diesel engine is set to 10, 25, 50, 75, and 100% under the condition of a constant speed of 2200 rpm. In addition, a low-speed and low-load operating point is added with a load and speed of 25% and 1000 rpm, respectively. The schematic diagram of all the working points is shown in Figure 4.
Figure 4.
Schematic diagram of the engine operating condition.
3. Results and Discussion
3.1. Power and Fuel Consumption
Figure 5 shows the torque characteristics of the engine equipped with DOC + SDPF aftertreatment at 2200 rpm under different load operating conditions. As the engine load increases, the diesel engine torque increases. The maximum torque can reach 330 N·m. Figure 6 shows that at this speed, the fuel consumption gradually decreases with the rise of load. The fuel consumption rate reduced from 475 to 200 g/kW·h. It can be concluded that there is no significant difference between the fuel consumption rate and dynamic performance of the engine with DOC + SDPF and the original engine.
Figure 5.
Engine torque under different engine loads.
Figure 6.
Engine fuel consumption under different engine loads.
Figure 7 shows the relationship between engine speed and fuel consumption under the condition of a 75% load. It was seen from the figure that fuel consumption increases linearly with the increase of engine speed.
Figure 7.
Engine fuel consumption at different engine speeds.
3.2. Particulate Emissions
Figure 8 shows the temperature at the DOC inlet, DOC outlet, and SDPF outlet under different loads. It can be found that with the increase of load, the temperature at each position gradually rises, and under the same operating condition, the temperature at the DOC inlet is higher than the DOC outlet temperature, and the DOC outlet temperature is higher than the SDPF outlet temperature. The temperature will directly affect the activity of the catalyst, thus affecting the conversion efficiency of SPDF for gas pollutants. The temperature of DOC inlet gas gradually increases from 275 °C under a 10% load condition to 470 °C under a 100% load condition.
Figure 8.
Temperature under different engine loads.
Figure 9 shows the back pressure at the DOC inlet, DOC outlet, and SDPF system outlet under different load conditions. It can be found that with the increase of load, the maximum back pressure of the DOC inlet can reach 18 kPa.
Figure 9.
Back pressure under different engine loads.
Figure 10 shows the particulate emission number concentration (PN) under different load conditions at 2200 rpm. The PN first rises with the increase of the load, but the PN concentration decreases at high-load conditions. This is because the rise of exhaust flow under high-load conditions leads to the decrease of the PN concentration. It can be seen from Figure 6 that the PN after passing through the SDPF system decreases significantly and the filtration rate of PN is more than 95%. With the rise of load, the filtration efficiency of PN increases slightly. The ability of SDPF to oxidize SOF depends on the exhaust temperature and catalytic activity. Therefore, the low load will make the temperature low, which will make SDPF detrimental to the oxidation of particulates. Under all test conditions, the particulate concentration after SDPF treatment decreases by 1–2 orders of magnitude, and the number concentration is less than 5 × 105 #/cm3. Under low-temperature and low-load conditions, the filtration efficiency of SDPF can also achieve 96.4%, which also demonstrates the ability to filter PM of SDPF under low-temperature and low-load conditions.
Figure 10.
PN under different engine loads.
Figure 11 shows the particulate emission mass concentration under different load conditions at 2200 rpm. The figure shows that the change of particulate emission of the diesel engine is like the trend of PN, which also increases at first and then decreases with the increase of load. When the engine is at 75% load, the particulate emission mass concentration reaches the peak, which is about 11000 μg/m3, and when under low load (10%), the PM emission is about 3000 μg/m3. The filtration efficiency of SDPF for PM is more than 90%, up to 96%, and the PM emission after SDPF filtration can be controlled at 280–380 μg/m3. It could be found that even under low-temperature and low-load conditions, the filtration efficiency of PM by SDPF could also reach 90.7%.
Figure 11.
PM under different engine loads.
Figures 12 and 13 show the distribution of the PN concentration of each particulate size. Under the operating condition of 2200 rpm and 50% load, the particulate size is mainly distributed around 50 nm, and the number of particulates decreases significantly by about 1 order of magnitude after passing through the SDPF system. Under the 100% load condition, the number of small-size particulates is more, and it can also be found that the number of particulates decreases significantly through the SDPF system. The number of particulates with a particulate size of 50 nm at the DOC inlet of the engine is about 3 × 106, which decreases to about 3 × 105 after being filtered by the SDPF system. The new regulation of emission is strict with the PN of particulate size between 10 and 23 nm, and the SDPF is capable of reducing the PN of particulate size between 10 and 23 nm by 1–2 orders of magnitude under high-load conditions (100% load).
Figure 12.
Particulate distribution under 50% load.
Figure 13.
Particulate distribution under 100% load.
Figure 14 shows the distribution characteristics of aggregated particulates and nuclear particulates at the DOC inlet, DOC outlet, and SDPF system outlet under different load conditions. After the capture and filtration of the SDPF system, the number of aggregated particulates is greatly reduced, and the proportion of nuclear particulates is significantly increased, indicating that SDPF has a more obvious filtration effect for particulates with a large particulate size. Comparing 50% load and 100% load conditions, the aggregated particulates under high-load conditions are slightly less than those under low-load conditions. SDPF filtering is mainly composed of Brownian diffusion, interception, and inertia. Brownian diffusion plays a major role, but with the increase of the particulate size, the effect weakens. The filtration effect of interception and inertia obstruction on large particulates is better, but the efficiency is lower than that of brown diffusion.31
Figure 14.
Distribution of aggregated and nuclear particulates.
Figure 15 shows the temperature at the DOC inlet, DOC outlet, and SDPF system outlet under different engine speeds. With the rise of engine speed, the temperature at each position gradually rises, and under the same working condition, the temperature at the engine exhaust port is greater than the DOC outlet temperature, and the DOC outlet temperature is greater than the SDPF outlet temperature. The temperature will directly affect the activity of the catalyst, thus affecting the conversion efficiency of SDPF for emission pollutants.
Figure 15.
Temperature under different speeds.
Figure 16 shows the back pressure at the DOC inlet, DOC outlet, and SDPF system outlet under different engine speed conditions. It could be found that with the increase of load, the maximum DOC inlet back pressure of the engine can reach 12 kPa.
Figure 16.
Pressure under different speeds.
Figure 17 shows the influence of different speeds on the PN emission and filtration efficiency under 75% load. From the figure, it is given that with the rise of speed, the emission of PM gradually increases from 3.0 × 106 to 1.5 × 107 (#/cm3) at 2200 rpm, reaching a peak. The filtration efficiency also increases gradually with the increase of speed, from 95 to 97.5%. The main influencing factor may be that with the increase of engine speed and temperature, it is more conducive to the filtration of particulates by SDPF.
Figure 17.
PN under different speeds.
Figure 18 shows the influence of different speeds on PM emission and SDPF filtration efficiency under a 75% load. From the figure, with the increase of speed, PM emissions generally show an upward trend. When the rotating speed is 2200 rpm, the PM concentration directly generated by the engine exhaust pipe is about 11000 μg/m3, after being treated by the SDPF system, the PM concentration is reduced to 300 μg/m3, and the capture efficiency of PM is about 96%. In addition, it could also be found that with the increase of rotating speed, the PM capture efficiency shows an upward trend. While the rotating speed increases from 1000 to 2200 rpm, the PM capture efficiency of SDPF increases from 87 to 96%. The main factor may be that after the speed increases and the load remains unchanged, the engine exhaust temperature increases, which improves the rate of the catalytic reaction and increases the PM capture efficiency.
Figure 18.
PM under different speeds.
3.3. Emissions of Gaseous Pollutants
The NOx emission under different load conditions at a speed of 2200 rpm is shown in Figure 19. It could be found that under a speed of 2200 rpm, the NOx emission increases with the rise of load. DOC has no obvious effect on the NOx emission. Because SDPF is coated with an SCR catalyst, urea enters SDPF through the injection port. After pyrolysis, hydrolysis, adsorption, and desorption, NH3 is generated to react with NOx to generate N2 and H2O so as to reduce NOx emission.32,33
Figure 19.
NOx emission under different loads.
The conversion efficiency of SDPF for NOx gradually decreases with the increase of load. At 10% load, the conversion efficiency is about 99.4%, while at 100% load, the conversion efficiency is reduced to 86.9%. And it could be found that under low-load conditions, the conversion efficiency of SDPF for NOx is very high, which shows that SDPF has a significant effect on the conversion of NOx at low-temperature and low-load conditions.
Figure 20 shows the change of the HC content under different loads at 2200 rpm. With the increase of load, the combustion inside the engine is more complete and the exhaust temperature increases, resulting in the reduction of HC emission. When the load is 10%, the HC emission concentration is as high as 1050 ppm, while when the load is increased to 100%, the HC emission concentration is reduced to about 50 ppm. DOC plays a major role in the reduction of HC emissions. Its reaction efficiency of oxidizing HC at low load is higher than that at high load, up to 90%, and the conversion efficiency is about 60% at 100% load. The specific reaction equation is shown in (4). Because SDPF is internally coated with a catalyst, it also has a certain reduction effect on HC, but the effect is far less than DOC.34
Figure 20.
THC emission under different loads.
Figure 21 focuses on the emission characteristics of CO under different loads at 2200 rpm. The emission of CO decreases with the increase of load. DOC mainly plays a major role in the reduction of CO emissions, and its reaction equation is shown in (5). The original emission of CO gradually decreases with an increase in engine load. As the engine load increases, the combustion is more sufficient, which reduces the emission of CO. As for the conversion efficiency of DOC oxidation of CO, it first increases and then decreases with the rise of load. The possible reason is that with the increase of load, the emission temperature rises, making part of CO2 reduced to CO.34
Figure 21.
CO emission under different loads.
When the load is 75%, the characteristics of the NOx emission concentration under different speed conditions are shown in Figure 22. While the rotating speed increases, the emission concentration of NOx gradually decreases and DOC has little effect on NOx. In general, the NOx concentration at the SDPF inlet tends to decrease as the engine speed increases, which is mainly due to the shortened reaction time of N2 and O2 in the high-temperature cylinder. When the speed is 1000 rpm, the NOx emission of the engine is about 700 ppm, while when the speed reaches 2200 rpm, the NOx emission is about 260 ppm. The conversion efficiency of SDPF for NOx is basically maintained at about 97%, indicating that the speed has little effect on the conversion efficiency.
Figure 22.
NOx emissions at different engine speeds.
Figure23 shows the HC emission concentration under different speed conditions at a 75% load. It can be seen that with the increase of rotating speed, the HC emission concentration decreases first and then increases. The increase is due to the increase of engine internal temperature and more complete combustion with the increase of rotating speed. With the continuous increase of rotating speed, the reaction time of combustion decreases and the combustion is incomplete, which increases the HC emission concentration. The conversion efficiency of HC is maintained at about 60–70%, basically unchanged.
Figure 23.
THC emissions under different engine speeds.
Figure 24 mainly shows the emission concentration of CO under different speed conditions. The emission concentration of CO basically remains unchanged with the increase of rotating speed, and the conversion efficiency of DOC to CO basically remains above 99% with the increase of rotating speed, indicating that the conversion efficiency of DOC is higher under the working condition of 75% load; therefore, it proves that the conversion efficiency of HC can be maintained at a higher level under the working condition of high load.
Figure 24.
CO emissions at different engine speeds.
NOx emissions under low-temperature and low-load conditions will become an important condition for future regulations, so it is necessary to conduct a study under this condition. The working load is 25%, and the engine speed is 1000 rpm.
From Table 5, it could be found that DOC + SDPF has a significant effect on the filtration and conversion efficiency of both PM and NOx under low-temperature and low-load conditions. The PM and PN filtration efficiencies are both above 90%, while the NOx conversion efficiency is 91.43%.
Table 5. Emission Characteristics under Low Temperature and Low Load.
| load (%) | speed (rpm) | PM filtration efficiency (%) | PN filtration efficiency (%) | NOx conversion efficiency (%) |
|---|---|---|---|---|
| 25 | 1000 | 94.37 | 90.36 | 91.43 |
4. Conclusions
Aiming at the current aftertreatment technology, this paper puts forward the solution of the DOC + SDPF system, designs a reasonable test process and equipment, and verifies the emission reduction effect of light diesel engine equipped with DOC + SDPF by collecting the emission data at the DOC inlet, DOC outlet, and SDPF outlet at the same time, to meet the new strict emission regulations and achieve the double carbon goal. Therefore, the purpose of this paper is to discuss in detail the impact of steady-state operation of the DOC + SDPF aftertreatment system on engine performance, fuel economy, and emissions under various working conditions, especially under low-temperature and low-load conditions, to evaluate the feasibility and power of this aftertreatment system. The research done in this paper is summarized as follows:
-
1.
DOC + SDPF has good filtration and conversion efficiency for PM and gaseous pollutants under high-speed and high-load conditions. Under 100% load and 2200 rpm conditions, the particulate filtration efficiency can reach over 90% and the conversion efficiency of gaseous pollutants is over 85%.
-
2.
The number of particulates rises with the increase in rotating speed. SDPF performs well at 100% load conditions for PM with particle sizes of 10–23 nm, reducing particle concentrations by 1–2 orders of magnitude.
-
3.
Under low-temperature and low-load conditions, DOC + SDPF has a high filtration and conversion efficiency for PM and gaseous pollutants with a PM filtration efficiency of 94.37% and a NOx conversion efficiency of over 90%.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (no. 52076154). The authors would like to thank editors and anonymous reviewers for their suggestions to improve the paper.
The authors declare no competing financial interest.
References
- Toni K.; Matilainen P.; Scheder D.. Particle oxidation catalyst - from diesel to GDI - studies on particulate number and mass efficiency[C]. SAE Technical Papers, 2012, 2012–01–0845.
- Liu Z.; Ge Y.; Tan J.; He C.; Shah A. N.; Ding Y.; Yu L.; Zhao W. Impacts of continuously regenerating trap and particle oxidation catalyst on the NO2 and particulate matter emissions emitted from diesel engine. J. Environ. Sci. 2012, 24 (4), 624–631. 10.1016/S1001-0742(11)60810-3. [DOI] [PubMed] [Google Scholar]
- Liu Z.; Ge Y.; Johnson K. C.; Shah A. N.; Tan J.; Wang C.; Yu L. Real-world operation conditions and on-road emissions of Beijing diesel buses measured by using portable emission measurement system and electric low-pressure impactor. Sci. Total Environ. 2011, 409 (8), 1476–1480. 10.1016/j.scitotenv.2010.12.042. [DOI] [PubMed] [Google Scholar]
- Moyebi O. D.; Fatmi Z.; Carpenter D. O.; Santoso M.; Siddique A.; Khan K.; Zeb J.; Hussain M. M.; Khwaja H. A.; et al. Fine particulate matter and its chemical constituents’ levels: A troubling environmental and human health situation in Karachi, Pakistan. Sci. Total Environ. 2023, 868, 161474. 10.1016/j.scitotenv.2023.161474. [DOI] [PubMed] [Google Scholar]
- Young L. H.; Liou Y. J.; Cheng M. T.; Lu J. H.; Yang H. H.; Tsai Y. I.; Wang L. C.; Chen C. B.; Lai J. S. Effects of biodiesel, engine load and diesel particulate filter on nonvolatile particle number size distributions in heavy-duty diesel engine exhaust. J. Hazard. Mater. 2012, 199–200, 282–289. 10.1016/j.jhazmat.2011.11.014. [DOI] [PubMed] [Google Scholar]
- Schejbal M.; Štěpánek J.; Kočí P.; Marek M.; Kubíček M.; et al. Sequence of monolithic converters DOC-CDPF-NSRC for lean exhaust gas detoxification: A simulation study. Chem. Eng. Process. 2010, 49, 943–952. 10.1016/j.cep.2010.05.005. [DOI] [Google Scholar]
- López J. M.; Jiménez F.; Aparicio F.; Flores N. On-road emissions from urban buses with SCR+Urea and EGR+DPF systems using diesel and biodiesel. Transp. Res. Part D 2009, 14, 1–5. 10.1016/j.trd.2008.07.004. [DOI] [Google Scholar]
- Zhan R.; Li M.; Lin S.. Updating China heavy-duty on-road diesel emission regulations. SAE Technical Papers, 2012, 10.4271/2012-01-0367. [DOI] [Google Scholar]
- Zi X. Y.; Ning Z.; An X. B. The Influence of Filter on the Distribution of Size and Number Density of Diesel Exhaust Particulate. Trans. Chin. Soc. Int. Combust. Engines 2001, 19 (4), 305–308. [Google Scholar]
- Palma V.; Ciambelli P.; Meloni E.; Sin A. Study of the catalyst load for a microwave susceptible catalytic DPF. Catal. Today 2013, 216, 185–193. 10.1016/j.cattod.2013.07.012. [DOI] [Google Scholar]
- Zhang Z.; Fan X.; Song C.; Lu W.; Li H.; Wang P. The effect of dual dielectric barrier discharge non-thermal plasma on the emission characteristics of diesel engine. Environ. Challenges 2022, 9, 100652. 10.1016/j.envc.2022.100652. [DOI] [Google Scholar]
- Shi Z.; Peng Q.; E J.; Xie B.; Wei J.; Yin R.; Fu G. Mechanism, performance and modification methods for NH3-SCR catalysts: A review. Fuel 2023, 331, 125885. 10.1016/j.fuel.2022.125885. [DOI] [Google Scholar]
- Russell A.; Epling W. S. Diesel Oxidation Catalysts. Catal. Rev. 2011, 53 (4), 337–423. 10.1080/01614940.2011.596429. [DOI] [Google Scholar]
- Umeno T.; Hanzawa M.; Hayashi Y.. et al. Development of new lean NOx trap technology with high sulfur resistance[C]. SAE Technical Papers, 2014,2014–01–1526.
- Pereda-Ayo B.; De La Torre U.; González-Marcos M. P.; González-Velasco J. R.; et al. Influence of ceria loading on the NOx storage and reduction performance of model Pt–Ba/Al2O3 NSR catalyst. Catal. Today 2015, 241, 133–142. 10.1016/j.cattod.2014.03.044. [DOI] [Google Scholar]
- Castoldi L.; Righini L.; Matarrese R.; Lietti L.; Forzatti P.; et al. Mechanistic aspects of the release and the reduction of NO stored on Pt–Ba/Al2O3. J. Catal. 2015, 328 (1), 270–279. 10.1016/j.jcat.2015.02.005. [DOI] [Google Scholar]
- Kang W.; Choi B.; Kim H. Characteristics of the simultaneous removal of PM and NOx using CuNb-ZSM-5 coated on diesel particulate filter. J. Ind. Eng. Chem. 2013, 19 (4), 1406–1412. 10.1016/j.jiec.2013.01.004. [DOI] [Google Scholar]
- Johansen K.; Bentzer H.; Kustov A.. et al. Integration of vanadium and zeolite type SCR functionality into DPF in exhaust after-treatment systems - advantages and challenges[C]. SAE Technical Papers, 2014, 2014–01–1523.
- Taylor M.; Kaneda A.; Kai R.. et al. Development of improved SCRonDPF design for future tighter regulations and reduced system packaging [C]. SAE Technical Papers, 2018,2018–01–0344.
- Rappé K. G.; Herling D. R.; Lee J.; Stewart M.. Combination & integration of DPF-SCR aftertreatment technologies; Presentation at US Department of Energy: Detroit, MI, 3–6 October 2011. [Google Scholar]
- Cavataio G.; Girard J. W.; Lambert C. K.. Cu/zeolite SCR on high porosity filters: laboratory and engine performance evaluations[C]. SAE Technical Papers, 2009,2009–01–0897.
- Ballinger T.; Cox J.; Konduru M.. et al. Evaluation of SCR catalyst technology on diesel particulate filters [C]. SAE Technical Papers, 2009,2009–01–0910.
- Karamitros D.; Koltsakis G. Model-based optimization of catalyst zoning on SCR-coated particulate filters. Chem. Eng. Sci. 2017, 173, 514–524. 10.1016/j.ces.2017.08.016. [DOI] [Google Scholar]
- Mohan S.; Dinesha P.; Kumar S. NOx reduction behaviour in copper zeolite catalysts for ammonia SCR systems: A review. Chem. Eng. J. 2020, 384, 123253. 10.1016/j.cej.2019.123253. [DOI] [Google Scholar]
- Rappé K. G. Integrated Selective Catalytic Reduction–Diesel Particulate Filter aftertreatment: Insights into Pressure Drop, NO x Conversion, and Passive Soot Oxidation Behavior. Ind. Eng. Chem. Res. 2014, 53 (45), 17547–17557. 10.1021/ie502832f. [DOI] [Google Scholar]
- Mehsein K.; Delahay G.; Villain N.; Moral N. Comparison of Vehicle Aged SCR Catalyst on a Particulate Filter (SCRF) with Oven Aged Equivalent. Int. J. Automot. Mech. Eng. 2019, 16 (3), 6918–6930. 10.15282/ijame.16.3.2019.07.0519. [DOI] [Google Scholar]
- Cumaranatunge L.; Chiffey A.; Stetina J.; McGonigle K.; Repley G.; Lee A.; Chatterjee S.; et al. A Study of the Soot Combustion Efficiency of an SCRF® Catalyst vs a CSF During Active Regeneration. Emiss. Control Sci. Technol. 2017, 3, 93–104. 10.1007/s40825-016-0059-6. [DOI] [Google Scholar]
- Millo F.; Rafigh M.; Fino D.; Miceli P.; et al. Application of a global kinetic model on an SCR coated on Filter (SCR-F) catalyst for automotive applications. Fuel 2017, 198, 183–192. 10.1016/j.fuel.2016.11.082. [DOI] [Google Scholar]
- Rose D.; George S.; Warkins J.. et al. A new generation high porosityduratrap at for integration of De NOx functionalities [C].Presentation at 9th International Car Training Institute Conference -SCR Systems, Stuttgart, 2013.
- Chen Y. j.; Tan P. q.; Duan L. s.; Liu Y.; Lou D. m.; Hu Z. y.; et al. Emission characteristics and performance of SCR coated on DPF with different soot loads. Fuel 2022, 330, 125712. 10.1016/j.fuel.2022.125712. [DOI] [Google Scholar]
- Beatrice C.; Iorio S. D.; Guido C.; Napolitano P. Detailed characterization of particulate emissions of an automotive catalyzed DPF using actual regeneration strategies. Exp. Therm. Fluid Sci. 2012, 39, 45–53. 10.1016/j.expthermflusci.2012.01.005. [DOI] [Google Scholar]
- Cho C. P.; Pyo Y. D.; Jang J. Y.; Kim G. C.; Shin Y. J. NO x reduction and N 2 O emissions in a diesel engine exhaust using Fe-zeolite and vanadium based SCR catalysts. Appl. Therm. Eng. 2017, 110, 18–24. 10.1016/j.applthermaleng.2016.08.118. [DOI] [Google Scholar]
- Shrestha S.; Harolda M. P.; Kamasamudram K.; Yezerets A. Selective oxidation of ammonia on mixed and dual-layer Fe-ZSM-5+Pt/Al2O3 monolithic catalysts. Catal. Today 2014, 231, 105–115. 10.1016/j.cattod.2014.01.024. [DOI] [Google Scholar]
- Zhang Z.; Tian J.; Li J.; Cao C.; Wang S.; Lv J.; Zheng W.; Tan D.; et al. The development of diesel oxidation catalysts and the effect of sulfur dioxide on catalysts of metal-based diesel oxidation catalysts: A review. Fuel Process. Technol. 2022, 233, 107317. 10.1016/j.fuproc.2022.107317. [DOI] [Google Scholar]