Emission Durability of a China-6 Light-Duty Gasoline Vehicle

Abstract

Reducing vehicle emissions and minimizing the impact of the transportation industry on the environment are key to achieving global sustainable development goals. China-6 emissions standard requires light-duty gasoline vehicles to meet the emissions limit requirements for particulate number (PN) emissions. Therefore, light-duty gasoline vehicles must also be equipped with a gasoline particulate filter (GPF) in addition to the three-way catalytic converter (TWC) and meet the emissions limit requirements within a durability mileage of 200,000 km. Currently, there is very little research on the impact of GPF degradation on the fuel economy and emissions of gasoline vehicles, especially on the newly restricted N₂O emissions. This study adopts the vehicle test method to study the deterioration of emissions of a China-6 light-duty gasoline vehicle with driving mileage. The research results show that the emissions of gasoline vehicles still meet the emissions limit after driving 200,000 km, and the deterioration factors of various emission pollutants are less than the recommended deterioration factors. The gasoline vehicle’s carbon dioxide (CO₂) emission and fuel consumption increase by less than 3%, indicating that the aging of vehicle components, including TWC and GPF, has no significant impact on vehicle fuel economy.

1. Introduction

Controlling motor vehicle emissions is an important means to protect the atmospheric environment and promote the sustainable development of the automotive industry and human society. The emissions of hydrocarbons (HCs), carbon monoxide (CO), nitrogen oxide (NOx), and particulate matter (PM) from vehicles have caused serious air pollution [1,2]. These substances have been recognized as the main contributors to haze and photochemical pollution, causing serious influences on human health and ecosystems [3,4]. Although some environmentally friendly vehicles, such as electric vehicles [5,6], have begun to be mass-produced and put into use, petroleum-fuel vehicles are expected to account for a higher proportion in the coming decades, and vehicle emissions control will remain a major challenge. Therefore, the emissions regulations for vehicles at home and abroad are becoming increasingly strict, leading to lower initial vehicle emissions, which will deteriorate with the increase in vehicle mileage due to the wear and deterioration of engine components [7], especially the aging of after-treatment systems. A large amounts of annual vehicle emissions inspection data and road test data indicate that vehicle emissions will increase with increasing mileage [8,9,10,11]. Therefore, the China-6 light-duty vehicle emissions standard stipulates that the exhaust emissions from China 6b light-duty vehicles meet the emissions limit within the mileage of 200,000 km [12], and considering the serious harm of fine particulate matter from gasoline vehicles to human health [13,14], the China-6 light-duty vehicle emissions standard has put forward control requirements for PN emissions, with a PN emissions limit of 6 × 10¹¹#/km. This means that gasoline vehicles need to use GPF in addition to a TWC.

The vast majority of vehicles used in urban transportation is gasoline vehicles, which emit more CO and HC, with CO emissions exceeding 80% of the total vehicle CO emissions, HC emissions exceeding 70% of the total vehicle HC emissions, and NOx emissions accounting for approximately 20–30% of the total vehicle NOx emissions [15,16]. Gasoline vehicles generally use a TWC to remove exhaust pollutants emitted from gasoline engines. Modern, commercial TWCs generally contain active precious metals, such as platinum (Pt), rhodium (Rh), and palladium (Pd), as well as oxides, such as Al₂O₃ and CexZr1-xO₂ [17]. Due to the long-term and harsh working environment, the TWC of gasoline vehicles is prone to aging [18,19], resulting in a significant increase in emissions. Therefore, the study of the emissions degradation characteristics of gasoline vehicles is a very important and complex research topic, which not only evaluates whether their emissions can meet the durability requirements stipulated by regulations, but also to provide a reference for the improvement of gasoline vehicle emissions control technology.

TWC aging is a very complex process of physical and chemical changes, which can be caused by catalyst overheating, chemical poisoning, and mechanical damage [19]. Thermal aging is the most common form of aging [20,21]. The prolonged exposure of catalysts to high-temperature environments can easily lead to the sintering of precious metals, phase transformation of coating structures, and melting of catalyst supports, resulting in a decrease in the catalyst-specific surface area and catalytic efficiency [20,21]. Engine misfire and ignition system malfunction can cause plenty of unburned HC to undergo oxidation reactions in the catalytic converter, leading to the overheating of the catalysts and serious thermal aging. At present, the TWC mostly adopts a tightly coupled arrangement, with the TWC located closer to the engine exhaust port and higher temperatures, making it susceptible to thermal shock.

Ideally, obtaining the emissions deterioration characteristics of vehicles requires long-term tracking testing, but the testing time is long, the cost is high, and the internal data testing of the TWC is difficult. Therefore, domestic and foreign emissions regulations allow production enterprises to use alternative TWC aging test methods [22], including high-temperature fuel cut aging, the multi-stage mode aging cycle [23], etc. The durability standard bench cycle (SBC) test method for after-treatment devices proposed in the China 6 emissions standard is the multi-stage mode aging cycle [12]. This method utilizes thermal aging to accelerate the catalyst’s aging process by increasing its temperature. The SBC cycle includes an alternating air–fuel ratio and secondary air-injection conditions, and requires the use of an engine or burner as an exhaust gas generator to provide exhaust gas for TWC aging. The SBC cycle has strict requirements for exhaust air–fuel ratio and temperature at the inlet of the TWC [24]. After TWC aging, it needs to be reinstalled on the vehicle, and the vehicle needs to undergo type-I emissions testing in the laboratory to test vehicle emissions, which is used to assess the trend of vehicle emissions degradation with mileage. The SBC cycle is the TWC degradation performance test based on the high-temperature degradation mechanism of the TWC. It cannot fully reflect the actual situation of TWC aging during long-term vehicle operation. In addition, the TWC bench rapid aging method may not be suitable for the GPF. At present, there is no recognized aging method for gasoline vehicle GPF rapid aging at home and abroad. The evaluation of diesel particulate filter (DPF) aging characteristics mainly focuses on ash deposition, particle deposition, and DPF regeneration characteristics [25,26]. There are very few records of gasoline vehicle GPF rapid aging test research. Therefore, for gasoline vehicles equipped with a GPF, using whole-vehicle testing methods to evaluate their emissions durability performance is the most practical and effective method. Compared with pre-China-6 vehicles, the emissions from China-6 light-duty vehicles have significantly decreased [27,28,29], but there is very little research on the emissions durability of China-6 light-duty gasoline vehicles, especially light-duty gasoline vehicles equipped with a GPF. The GPF has been widely used in China-6b light-duty gasoline vehicles. Currently, there is also limited research on the impact of GPF degradation on the fuel economy and emissions of gasoline vehicles, especially on the newly restricted N₂O emissions. In order to reveal the emissions durability of China-6b light-duty gasoline vehicles, a China-6b light-duty gasoline vehicle was tested on a chassis dynamometer according to standard driving cycle over the durability distance of 200,000 km, and emissions tests were conducted at specified mileage intervals to evaluate the emissions aging status of the light gasoline vehicle. Furthermore, the deterioration factors of exhaust emission pollutants were calculated, and the degradation characteristics of CO₂ emissions and fuel economy with vehicle mileage were analyzed.

2. Experimental Setup and Methodology

2.1. Test Vehicle

The test vehicle was a China 6b direct injection gasoline vehicle with an engine displacement of 2.0 L and was a five-seater sedan, classified as an M1 vehicle [12]. The exhaust after-treatment system of the gasoline vehicle had a TWC and GPF, with the front stage unit being the TWC and the rear stage unit being the catalytic GPF (CGPF) that combined TWC functions. The pore density (cpsi)/wall thickness (mil) of the TWC and CGPF were 600/3 and 300/8, respectively. The specifications of the test vehicle are shown in

Table 1. Specifications of the tested gasoline vehicle.

Vehicle Type	Emission Standard	Fuel Type	Fuel Injection System	Intake System	After-Treatment System	Curb Weight /kg	Engine Swept Volume /L	Engine Maximum Power /kW	Useful Life /km
M1	China-6b	gasoline	GDI	TC	TWC + CGPF	2020	2.0	185	200,000

.

2.2. Vehicle Aging Test and Evaluation Method

To evaluate the emissions durability performance of vehicles over their service life, the approved mileage accumulation (AMA) cycle and standard road cycle (SRC) were recommended as vehicle durability assessment cycles to simulate the aging effect of thermal aging on three-way catalysts throughout their useful life [12]. The US EPA developed AMA in the early stages for vehicles that were not equipped with catalytic converters at that time, so the cycle itself included a significant portion of low-speed cycles, mainly aimed at simulating engine carbon deposition. With the application of engine electronic control systems and after-treatment systems, vehicle emissions have further decreased, and EPA has developed SRC cycles with worse driving conditions than AMA cycles. The thermal aging degree of three-way catalysts caused by SRC and AMA cycles is significantly higher than the actual driving conditions of vehicles at the same mileage. The aging degree of the three-way catalyst accumulated in the AMA cycle and SRC cycle is three and four times that of the three-way catalyst under normal driving at the same mileage, respectively [30]. Therefore, using AMA and SRC cycles for gasoline vehicle emissions aging assessments can fully reflect the aging degree of gasoline vehicle emissions with mileage, even exceeding the normal aging level.

This study used the AMA cycle recommended by the China 6 light-duty vehicle emissions standard for gasoline vehicle aging [12]. The AMA cycle consisted of 11 sub-cycles, each with a mileage of 6 km and a maximum speed of 113 km per hour, including idle, constant speed, acceleration, and deceleration conditions, as shown in Figure 1.

At set mileage intervals during the gasoline vehicle aging test, vehicle emissions were measured using the WLTC procedure, and the carbon balance method was used to calculate the fuel economy of the vehicle. Finally, the deterioration trend of gasoline vehicle emissions with driving mileage was evaluated and analyzed.

To accurately control the vehicle aging test conditions, the vehicle aging driving cycle was conducted on a durability test chassis dynamometer. An autopilot was used to control the accelerator pedal, brake, and shift lever to automatically follow the aging driving cycle speed curve to ensure that the vehicle speed fully complied with the aging driving cycle specified by the regulations. The testing equipment used is shown in

Table 2. Experimental equipment.

Name	Manufacturer	Model
Chassis dynamometer	Horiba (Kyoto, Japan)	EMS-CD48L 2WD
Autopilot	WITT GmbH (Weiden, Germany)	FA 2000-END

.

After the vehicle reached the set mileage point during the aging operation, it was removed from the durability chassis dynamometer for maintenance, sent to the emissions-testing chamber for emissions testing, and then returned to the aging test bench to continue the durability test. During the entire test period, the vehicle needed to be stopped for each refueling operation. The vehicle used gasoline that meets China 6 emissions standard, and the parameters for gasoline are shown in

Table 3. Gasoline parameters.

Type	Density at 15 °C/(kg/m3)	Vapor Pressure/kPa	Research Octane Number	Sulfur Mass Fraction/10−6
95#gasoline	0.760	57.9	96.6	2.8

.

The first emissions test of the vehicle was conducted after driving 3000 km, and the second emissions test was conducted when the vehicle’s mileage reached 10,000 km. Afterward, we conducted an emissions test every 10,000 additional kilometers until the end of the endurance mileage, which was 200,000 km for the China 6b light-duty gasoline vehicle. The measurement results for the exhaust pollutants in each vehicle type-I emissions test should comply with the emissions limit values specified in

Table 4. Emissions limits of exhaust pollutants for the type-I emissions test.

CO/ (mg/km)	THC/ (mg/km)	NMHC/ (mg/km)	NOx/ (mg/km)	N2O/ (mg/km)	PM/ (mg/km)	PN/ (#/km)
500	50	35	35	20	3.0	6.0 × 1011

. The measurement results of all exhaust pollutants should be plotted as a function of driving distance, and the best-fit line connecting all the data points should be drawn using the least squares method. The calculation should not consider the test results of 0 km.

According to the China 6 emissions standard, the data can only be used to calculate the deterioration factor when the interpolated values of 6400 km and the endpoint of the endurance mileage on this straight line meet the emissions limit. For each pollutant, the deterioration factor (DF) of the exhaust pollutant should be calculated as a multiplier using the following equation:

$$DF={\displaystyle \frac{M_{i2}}{M_{i1}}}$$

(1)

where M_i1 is the emissions of pollutant i calculated through the 6400 km interpolation, g/km. M_i2 is the emissions of pollutant i calculated by interpolation at the endpoint of the endurance mileage in g/km.

If the deterioration factor is less than 1, it is considered as 1. The deterioration factors of gasoline vehicle exhaust pollutants should be less than or equal to the values in

Table 5. Recommended deterioration factors for a light-duty gasoline vehicle.

CO	THC	NMHC	NOX	N2O	PM	PN
1.8	1.5	1.5	1.8	1.0	1.0	1.0

.

2.3. Vehicle Emissions Testing Methods

To ensure the accuracy of vehicle exhaust emissions testing, an environmental test chamber was used in the laboratory to test the WLTC driving cycle emissions of a gasoline vehicle. The testing equipment used is shown in

Table 6. Experimental equipment.

Equipment Name	Manufacturer	Model
Environmental test chamber	Imtech (Schwäbisch, Germany)	EC45192327
Chassis dynamometer	Horiba (Kyoto, Japan)	EMS-CD48L 2WD COLD
Constant-volume sampling system	Horiba (Kyoto, Japan)	CVS-7400T
Emissions analyzer	Horiba (Kyoto, Japan)	MEXA-7200H
N2O analyzer	Horiba (Kyoto, Japan)	MEXA-1100QL
Particle counter	Horiba (Kyoto, Japan)	MEXA-2000SPCS

and Figure 2.

The environmental test chamber adopts an automatic control system to provide a constant temperature and humidity environment. The temperature of the type-I emissions test chamber was controlled at 23 °C ± 5 °C, and the absolute humidity was within the range of 5.5~12.2 g/kg (water/dry air). The chassis dynamometer simulates and applies the total vehicle resistance while driving. The CVS-7400T (Horiba, Kyoto, Japan) constant-volume sampling system was used to measure the flow rate of the diluted gas. The MEXA7200H (Horiba, Kyoto, Japan) emissions analyzer was used to measure CO, CO₂, THC, NMHC, and NOx. CO and CO₂ were measured using the nondispersive infrared (NDIR) absorption method, the THC was measured using the hydrogen flame ionization (FID) method, the NMHC was measured by the meteorological chromatography method, and NOx was measured using the chemiluminescent detector (CLD). N₂O was measured using an MEXA-1100QL (Horiba, Kyoto, Japan) laser infrared spectrometer; the measurement of particulate number emissions adopted a MEXA-2000SPCS (Horiba, Kyoto, Japan) counter based on the condensation ion method, with the first and second dilution coefficients set to 10 and 15, respectively. In order to reduce the impact of pollutant components in the background air on the measurement results, a dilution air refinement system (DAR) was used to remove CO, NOx, and HC from the background air.

The vehicle emissions were tested over the WLTC driving cycle, which is shown in Figure 3 [31]. The WLTC driving cycle lasts for a total of 1800 s and consists of four parts: low-speed section, medium-speed section, high-speed section, and ultra-high-speed section, accounting for 33%, 24%, 25%, and 18% of the total operating time, respectively. The total driving distance of the WLTC is 23.26 km, including 3.1 km for low-speed conditions, 4.75 km for medium-speed conditions, 7.16 km for high-speed conditions, and 8.25 km for ultra-high-speed conditions, accounting for 13%, 20%, 31%, and 36% of the total driving distance, respectively. The average speed and maximum speed of the WLTC cycle are 46.5 km/h and 131.3 km/h, respectively.

The mass emissions factor of gas component i for the entire WLTC cycle is calculated by

$$m_{\mathrm{i}}={\displaystyle \frac{V_{\mathrm{mix}}\times { \mathsf{\rho }}_{\mathrm{i}}\times k_{\mathrm{H}}\times C_{\mathrm{i}}\times {10}^{-6}}{\mathrm{d}}}$$

(2)

where m_i is the mass emissions of gaseous component i, g/km; V_mix is the volume of diluted exhaust gas, L/test; ${\mathsf{\rho }}_{\mathrm{i}}$ is the density of gaseous component i, g/L; k_H is the humidity correction coefficient for calculating the emissions mass of nitrogen oxides; C_i is the concentration of gaseous component i, ppm; and d is the actual driving distance of the test cycle, km.

The mass emissions factor of PM in the whole WLTC cycle is calculated by

$$\mathrm{Mp}={\displaystyle \frac{{\mathrm{V}}_{\mathrm{mix}}\times {\mathrm{P}}_{\mathrm{e}}}{{\mathrm{V}}_{\mathrm{ep}}\times \mathrm{d}}}$$

(3)

where Mp is the PM emissions factor, g/km; P_e is the mass of particulate matter collected with filter paper, mg; and V_ep is the diluted gas volume flowing through particulate-matter filter paper, m³.

The formula for calculating the particulate number (PN) per unit mileage is as follows:

$$\mathrm{PN}={\displaystyle \frac{{\mathrm{V}}_{\mathrm{mix}}\times \mathrm{k}\times \left(\overline{{\mathrm{C}}_{\mathrm{s}}}\times \overline{{\mathrm{f}}_{\mathrm{r}}}-{\mathrm{C}}_{\mathrm{b}}\times \overline{{\mathrm{f}}_{\mathrm{rb}}}\right)\times {10}^3}{\mathrm{d}}}$$

(4)

where PN is the emitted particle number, #/km; k is the correction coefficient; $\overline{{\mathrm{C}}_{\mathrm{s}}}$ is the average particle concentration in the diluted exhaust after correction, #/cm³; $\overline{{\mathrm{f}}_{\mathrm{r}}}$ is the average particle concentration condensation coefficient of the volatile particle remover set for dilution during the experiment; C_b is the particle concentration in the background dilution air; and $\overline{{\mathrm{f}}_{\mathrm{rb}}}$ is the average particle concentration condensation coefficient of the volatile particle remover set for background dilution gas.

The vehicle travel distance, d, over the WLTC cycle is calculated by

$$d={{\displaystyle \int }}_{{\mathrm{t}}_1}^{{\mathrm{t}}_2}v\mathrm{dt}$$

(5)

where v is the vehicle speed, km·h⁻¹; t₁ and t₂ are the start and end times of the WLTC cycle, respectively.

2.4. Vehicle Fuel Consumption Calculation

The gasoline vehicle’s fuel consumption per 100 km over the driving cycle is calculated using the carbon balance method [32].

$${\mathrm{Q}}_{\mathrm{L}}={\displaystyle \frac{0.1154}{\mathsf{\rho }}}\left[\left(0.273\times {\mathrm{E}}_{{\mathrm{CO}}_2}\right)+\left(0.429\times {\mathrm{E}}_{\mathrm{CO}}\right)+\left(0.866\times {\mathrm{E}}_{\mathrm{HC}}\right)\right]$$

(6)

where Q_L is the gasoline vehicle’s fuel consumption in L/(100 km); ${\mathrm{E}}_{{\mathrm{CO}}_2}$, E_CO, and E_HC are the emissions factors of CO₂, CO, and HC, respectively, in g/km; and $\mathsf{\rho }$ is the gasoline density, g/L.

3. Results and Discussion

3.1. Analysis of Durability Characteristics of CO, THC, NMHC, and NOx Emissions

The CO, THC, NMHC, and NOx emissions of the vehicle are displayed in Figure 4, which shows that the vehicle emissions of CO, THC, NMHC, and NOx fluctuate with the increase in driving distance. The overall trend is that the emissions increase with the increase in driving distance, and the emissions test results within 200,000 km are all below the standard limits.

The experimental results indicate that, after long-term use, the performance of the three-way catalytic converter deteriorates, and its purification effect on CO, HC, and NOx is weakened. The deterioration of three-way catalytic converters is generally caused by thermal aging effects and chemical poisoning by phosphorus and sulfur in the exhaust gas, often due to the combined effects of various factors. Therefore, improving the quality of fuel and lubricating oil is also crucial for extending the service life of the TWC. In addition, the aging, deterioration, and wear of other engine components can also cause changes in their emissions characteristics, such as the aging of the air–fuel ratio sensor and temperature sensor, and improper use, maintenance, and repair are all factors that contribute to the deterioration of vehicle emissions. Therefore, improving the reliability and durability characteristics of the entire engine, as well as maintaining and using it normally, is the fundamental measure to ensure the durability characteristics of the vehicle’s emissions.

3.2. Analysis of N₂O Emissions Durability Characteristics

The durability characteristics of N₂O pollutant emissions from vehicles are shown in Figure 5.

Research has shown that vehicles without a TWC have lower N₂O emissions, while gasoline engines with a TWC have a significant increase in N₂O emissions [33,34,35]. N₂O generation mainly occurs in the early stages of catalyst warm-up, and when the catalyst reaches a normal temperature, N₂O emissions decrease. N₂O emissions are mainly formed in the early stages of the catalyst, and as the catalyst reaches an equilibrium temperature, N₂O emissions decrease. According to the test results, the N₂O emissions values do not exceed the emissions limit. The fluctuation in N₂O emissions throughout the entire service life of the vehicle is not significant, which means that N₂O emissions do not show a significant trend of change with the aging of the vehicle’s three-way catalytic converter.

3.3. Analyses of PM and PN Emissions Durability Characteristics

The in-cylinder gasoline direct injection of gasoline engine leads to uneven fuel gas mixing in the cylinder’s local area, resulting in oxygen-deficient areas in the cylinder and the generation of a large amount of particulate matter under high temperatures. Therefore, to meet the PN limit requirements of the China 6 light-duty vehicle emissions standard, in-cylinder direct-injection gasoline vehicles need to adopt a GPF to reduce the quality and quantity of particulate matter in the exhaust. The emissions durability of the gasoline vehicle PM and PN is shown in Figure 6.

Figure 6 shows that, within a cumulative driving distance of 40,000 km, the test results of PM mass and PN emissions show significant downward trends with the vehicle’s driving distance. After the accumulated driving distance exceeds 40,000 km, the downward trends of PM and PN emissions slow down, and there are fluctuations in emissions values. Throughout the vehicle’s entire useful life, PM and PN emissions meet the limit requirements. The introduction of a GPF is mainly aimed at reducing PN emissions in the vehicle’s exhaust. The GPF is constructed with many parallel, axial, honeycomb channels, and adjacent honeycomb channels are alternately blocked at both ends. When the engine exhaust gas flows through the walls of the honeycomb channels, the particles in the exhaust gas are trapped. The main mechanisms of particle capture include diffusion deposition, inertial deposition, gravity deposition, and interception deposition. The effect of particle interception and deposition is most closely related to the durability characteristics of the GPF. Before the formation of the carbon layer on the GPF’s channel wall, the effect of particle interception and deposition is not significant, but after the formation of the carbon layer, it plays a significant role in particle capture. The analysis of the experimental results shows that the process of gradual accumulation of trapped particles within a driving distance of 40,000 km is mainly due to the increasing interception and filtration effect on particulate matter. Therefore, the trend of PM and PN emissions reductions is obvious. After reaching a driving distance of 40,000 km, the formed particle adsorption layer is under the alternating effect of accumulation, regeneration, and elimination, and the thickness of the particle adsorption layer tends to stabilize. At the same time, an ash adsorption layer gradually forms, enhancing the effectiveness of particle filtration; however, the downward trend of PM and PN emissions slows down.

3.4. Analyses of CO₂ and Fuel Consumption Durability Characteristics

The durability characteristics of the gasoline vehicle’s CO₂ emissions and fuel economy are shown in Figure 7. The vehicle’s CO₂ emissions and fuel consumption do not change significantly with increasing mileage and are relatively stable. It can be seen that, under the premise of normal maintenance and repair, the aging of the after-treatment system, as well as the aging and wear of components of gasoline vehicles that meet the China-6 emissions standard, have no significant impact on the gasoline vehicle’s CO₂ emissions or fuel consumption within the durability mileage of 200,000 km.

3.5. Deterioration Factors

In order to evaluate the durability characteristics of the gasoline vehicle’s CO₂ emissions and fuel economy, linear regression equations for the test data of vehicle emissions and fuel consumption were established using the least squares method and expressed as

$$y=ax+b$$

(7)

The calculated factors, $a$ and $b$, as well as the deterioration factors of vehicle emissions and fuel economy are listed in

Table 7. The deterioration factors of vehicle emissions and fuel economy.

Item	CO	THC	NMHC	NOx	N2O	PM	PN	CO2	Fuel Consumption
a	0.0005	0.00005	0.00004	0.00005	−0.0000002	−0.000002	−0.00001	0.00003	0.000001
b	157.610	24.445	17.803	19.096	3.072	1.012	2.026	208.010	8.415
M1 (6400 km)	160.8100	24.7650	17.8040	19.4160	3.0711	0.9996	1.9623	208.2020	8.4217
M2 (200,000 km)	257.6100	34.4450	25.8030	29.0960	3.0324	0.6124	0.0263	214.0100	8.6153
Deterioration factor	1.602	1.391	1.449	1.499	0.987	0.613	0.013	1.028	1.023
Recommended deterioration factor	1.8	1.5	1.5	1.8	1.0	1.0	1.0

.

Table 7 indicates that the calculated deterioration factors of vehicle CO, THC, NMHC, NOx, N₂O, PM, and PN emissions are all less than the recommended deterioration factors specified by the China 6 light-duty vehicle emissions standard. The emissions of the tested gasoline vehicle fully meet the emissions regulations within its durability mileage of 200,000 km, despite the engine’s after-treatment deterioration. The CO₂ emissions and fuel consumption of the test gasoline vehicle increased by 2.8% and 2.3%, respectively, at the end of the durability mileage, indicating that GPF aging has no significant impact on vehicle fuel economy.

4. Conclusions

A China-6b light-duty gasoline vehicle was tested on the chassis dynamometer according to the standard AMA driving cycle over the durability mileage of 200,000 km to evaluate its emissions durability. The following conclusions are drawn:

The gasoline vehicle’s CO, THC, NMHC, and NOx emissions gradually increase with the increase in the driving mileage, indicating a deterioration trend in the TWC’s performance. However, the emissions of vehicle CO, THC, NMHC, and NOx are all below the regulatory limits within the durability mileage of 200,000 km.

The N₂O emissions of the gasoline vehicle for all tested WLTC cycles are lower than the emissions limit and relatively stable, meaning that the aging of the TWC has little impact on N₂O emissions, despite the TWC promoting N₂O formation.

As the particle interception effect of the GPF gradually increases, the emissions of PM and PN show a significant descending trend with the increase in vehicle mileage within 40,000 km. After the cumulative vehicle mileage exceeds 40,000 km, the downward trend of PM and PN emissions slows down. Throughout the gasoline vehicle’s useful life, PM and PN emissions meet the limit requirements, proving that the GPF can effectively reduce gasoline vehicle PM and PN emissions.

At the end of the durability mileage of 200,000 km, the gasoline vehicle’s CO₂ emissions and fuel consumption increased by less than 3%, indicating that the deterioration of the GPF and particle deposition within the GPF have no significant influence on the gasoline vehicle’s fuel economy.

The deterioration factors of the gasoline vehicle’s CO, THC, NMHC, NOx, N₂O, PM, and PN emissions are all less than the recommended deterioration factors specified by the China 6 emissions standard, indicating that, despite the presence of wear and tear on vehicle components aging engine exhaust after-treatment systems, the tested gasoline vehicle can meet the emissions regulations within its durability mileage under normal use and maintenance.