Light-duty Vehicle Test Cycle Research Articles

Monte Carlo Simulation Methodology to Assess the Impact of Ambient Wind on Emissions from a Light-Commercial Vehicle Running on the Worldwide-Harmonized Light-Duty Vehicles Test Cycle (WLTC)

A Monte Carlo simulation methodology is suggested in order to assess the impact of ambient wind on a vehicle’s performance and emissions. A large number of random wind profiles is generated by implementing the Weibull and uniform statistical distributions for wind speed and direction, respectively. Wind speed data are drawn from eight cities across Europe. The vehicle considered is a diesel-powered, turbocharged, light-commercial vehicle and the baseline trip is the worldwide harmonized light-duty vehicles WLTC cycle. A detailed engine-mapping approach is used as the basis for the results, complemented with experimentally derived correction coefficients to account for engine transients. The properties of interest are (engine-out) NO and soot emissions, as well as fuel and energy consumption and CO2 emissions. Results from this study show that there is an aggregate increase in all properties, vis-à-vis the reference case (i.e., zero wind), if ambient wind is to be accounted for in road load calculation. Mean wind speeds for the different sites examined range from 14.6 km/h to 24.2 km/h. The average increase in the properties studied, across all sites, ranges from 0.22% up to 2.52% depending on the trip and the property (CO2, soot, NO, energy consumption) examined. Based on individual trip assessment, it was found that especially at high vehicle speeds where wind drag becomes the major road load force, CO2 emissions may increase by 28%, NO emissions by 22%, and soot emissions by 13% in the presence of strong headwinds. Moreover, it is demonstrated that the adverse effect of headwinds far exceeds the positive effect of tailwinds, thus explaining the overall increase in fuel/energy consumption as well as emissions, while also highlighting the shortcomings of the current certification procedure, which neglects ambient wind effects.

Analysis of fuel consumption of China light duty vehicle test cycle for passenger car(CLTC-P)

Through the fuel consumption test of several listed vehicles in China, the basic fuel consumption results of cold start under CLTC-P cycle, the fuel consumption results of vehicles under the condition of air conditioning on, and the fuel consumption results of vehicles under the condition of air conditioning off are measured. At the same time, the differences between NEDC cycle and CLTC-P cycle in China's fuel consumption certification test are compared, and the results of fuel consumption test are combined The fuel consumption test results under CLTC-P cycle are higher than those under NEDC cycle, and the fuel consumption test procedures under Chinese condition are more in line with the actual driving situation in China.

Influence of Test Cycles on Energy Consumption Test of Electric Vehicles

In order to verify the necessity of the application of China Automotive Test Cycle which is constructed through actual driving data in china of more than 55 million kilometers in the energy consumption test of electric vehicles in China, this paper compares the characteristics of New European Test Cycle (NEDC), World-wide harmonized Light duty Test Cycle (WLTC) and China light-duty vehicle test cycle for passenger car(CLTC-P), and analyzes the differences of vehicle energy demand under different test cycles from theoretical and simulation point, simulation results show that the endurance mileage is longest and the energy recovery strategy is more effective under CLTC-P cycle. Finally, four types of vehicles are selected to carry out the endurance mileage test under these three test cycles. The test results are consistent with the simulation results. Therefore, in order to make the test results of electric vehicle energy consumption closer to the actual use of our country, CLTC-P should be selected to replace NEDC and WLTC cycle.

Experimental Study on The Performance of FCV in Standard Test Cycle

The experiments of one FCV (Fuel Cell Vehicle) are conducted in three standard cycle conditions of NEDC (New European Driving Cycle), WLTC (Worldwide Light-duty Test Cycle) and CLTC (China Light-duty vehicle Test Cycle), and the performance of stack power, temperature and system efficiency are compared and analysed. Results show that the variation range of fuel cell system efficiency is ordered as: WLTC > NEDC > CLTC. The efficiency of fuel cell system is highest in CLTC; the fuel cell stack power and temperature are relatively low; the hydrogen consumption is lowest(0.93kg/100km). According to the analysis on experimental data of FCV in NEDC, the output power of stack is proportional to accelerator pedal when the accelerator pedal opening is greater than 25%.

Application of shortening time test in battery electric range calculation of PEV based on CLTC-P

In order to obtain the actual results of battery electric range test, and meet the demand of fiscal subsidy policy introduction of new energy vehicles, some modifications of the standard GB/T 18386.1 Test Method for Energy Consumption and Range of Electric Vehicles- part1: Light-duty Vehicles are revised by drafting group. Such as China Light-duty vehicle Test Cycle for passenger car (CLTC-P), Shortened time test method, etc. To prove the reasonability of Shortened time test to measure battery electric range (BER) based on CLTC-P, two sets of vehicle tests were carried out. Results show that shortened time test greatly reduce test time, and the weighting factor setting of DS1 and DS2 is reasonable. Although some deviation between Shortened time test and consecutive cycle test exist, but not regularly. It is related to the vehicle energy regulation strategy individually. Finally, it is recommended that the test vehicle should be forced to break 10 minutes after the end of CSSM.

Comparative Analysis of China Light-duty Vehicle Test cycle for Passenger Car and Other Typical Driving Cycles

In 2019, China issued the first national standard for vehicle driving cycle, in which China light-duty vehicle test cycle for passenger car (CLTC-P) is the driving cycle for light-duty passenger cars. CLTC-P is of great significance to the development of China’s automobile industry, and has a great impact on the development and calibration of vehicles of automobile enterprises. In this paper, firstly, the driving characteristics of CLTC-P are analyzed systematically. Then it is compared with the third-party navigation big data to prove the rationality and effectiveness. Finally, CLTC-P is compared with other legal cycles in terms of time, distance, speed, and acceleration characteristics. The result shows that by comparing the characteristics of CLTC-P with other typical cycles and the GIS weighted results, the CLTC-P is more in line with Chinese reality and is significantly different from other typical cycles.

Research on exhaust emission characteristics and technical route under CLTC cycle

In this paper, the light duty that meets the China 6 emission standard is selected to study the emission characteristics of different emission control technology routes under China light-duty vehicle test cycle (CLTC). The results show that the cold start stage of CLTC cycle is still the stage with the most pollutant emissions. The THC, CO and NOx emissions of vehicles on the supercharged direct injection technology are higher than those on the naturally aspirated port fuel injection technology. In terms of reducing the exhaust emission, PHEV technology route is the best, followed by naturally aspirated PFI technology route, and then turbocharged direct injection with GPF route.

Impact of test cycle on mass, number and particle size distribution of particulates emitted from gasoline direct injection vehicles

This paper presents an investigation of emissions from gasoline direct injection (GDI) vehicles and analyzed the characteristics of emitted particulate matter (PM), the emission factors of particulate number (PN) and size distribution properties, including four test cycles: the new European driving cycle (NEDC), the worldwide harmonized light vehicle test cycle (WLTC), the USA federal test procedure-75 (FTP-75) and the China light-duty vehicle test cycle (CLTC). The results reveal that for China VI standard GDI vehicle, compared with CLTC, which is the newest test cycle according to realistic road conditions in China, the aforesaid evaluation indexes of FTP-75 and WLTC are basically higher due to their higher acceleration and deceleration ratio. Compared with hot start, a cold start followed by warming-up process has a significant impact on PN emissions over all test cycles and different test cycles show diverse sensitivity to the change of start-up conditions. The particles with a diameter of 5.6–23 nm (sub-23 nm) account for 43.1–57.7% of the total PN emission quantity for China V standard GDI vehicle, which is about 5–15% higher than that of theoretical assumptions. Different piecewise speed segments exhibited different impacts on PN characteristics when acceleration and deceleration reveal greater influence. Gasoline particulate filter (GPF) could effectively capture full-size particulates including fine particles as sub-23 nm particles, which is verified over FTP-75 and CLTC, while sub-23 nm PN emission is still at a high level over WLTC for its ultrahigh speed segment. There could have been an underestimation of the real particle number emitted from GDI vehicle while the emission of solid sub-23 nm particles was excluded under current emission regulations.

Development of China Light-Duty Vehicle Test Cycle

Driving cycles provide a basis for vehicle development and calibration and also serves as the foundation for energy consumption and emissions certification of vehicles. This paper presents the China Light-Duty Vehicle Test Cycle (CLTC) developed by the China Automotive Technology & Research Center (CATARC). First, the important steps and technical routes toward the CLTC development process are summarized. Second, the specific CLTC development process is presented in detail, including the data acquisition and data analysis procedures, weighting factor development and driving cycle construction. Then, the main driving characteristics of the New European Driving Cycle (NEDC), the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC), the Federal Test Procedure (FTP-75), the CLTC and the actual collected data are compared. The CLTC has low average speed, a high idle speed ratio and more frequent acceleration and deceleration characteristics. Finally, 70 vehicles are tested based on the NEDC, WLTC, and CLTC according to their legislative procedures in the vehicle emission laboratories of the CATARC and the manufacturers. The results show that the CLTC’s fuel consumption is much higher than that of the NEDC and WLTC, and CLTC can effectively reflect the actual fuel consumption of users.

Development of a Variable Valve Actuation Control to Improve Diesel Oxidation Catalyst Efficiency and Emissions in a Light Duty Diesel Engine

Growing interest has arisen to adopt Variable Valve Timing (VVT) technology for automotive engines due to the need to fulfill the pollutant emission regulations. Several VVT strategies, such as the exhaust re-opening and the late exhaust closing, can be used to achieve an increment in the after-treatment upstream temperature by increasing the residual gas amount. In this study, a one-dimensional gas dynamics engine model has been used to simulate several VVT strategies and develop a control system to actuate over the valves timing in order to increase diesel oxidation catalyst efficiency and reduce the exhaust pollutant emissions. A transient operating conditions comparison, taking the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC) as a reference, has been done by analyzing fuel economy, HC and CO pollutant emissions levels. The results conclude that the combination of an early exhaust and a late intake valve events leads to a 20% reduction in CO emissions with a fuel penalty of 6% over the low speed stage of the WLTC, during the warm-up of the oxidation catalyst. The same set-up is able to reduce HC emissions down to 16% and NOx emission by 13%.

Accuracy of range estimation of pure electric vehicles under compound conditions comparative analysis

In high and low temperature environments, especially in high-speed scenarios, the estimation accuracy of the range of electric vehicles is a pain point which is more concerned by consumers. Based on the China light-duty vehicle test cycle for passenger car, this paper deeply studies the estimation accuracy of the range of electric vehicles under different ambient temperature conditions. Further, a complex test cycle including long-distance in high-speed driving conditions is constructed, and the influence rule of the complex test cycle and high-speed vehicle speed on the estimation accuracy of cruising range is compared and analyzed through actual vehicle tests.

Analysis of Factors Affecting the Accuracy Evaluation of Range Estimation of Pure Electric Vehicles Based on CLTC-P

The estimation accuracy of the cruising range of electric vehicles is an important performance index of electric vehicles. Improving the accuracy of cruising range estimation is of great significance for improving the user acceptance of electric vehicles. This paper carried out vehicle tests under normal temperature environment based on China light-duty vehicle test cycle for passenger car (CLTC-P) under different battery state of charge and long-distance constant-speed driving, and use the determination coefficient to analyze and evaluate the accuracy of the metered range mileage. At the same time the paper deeply study the impact of different data collection frequencies and the vehicle’s metered range self-learning mode on the accuracy of the range mileage. This study provides theoretical support for the use of certain coefficients to study the accuracy of the estimated range of pure electric vehicles under unified scenarios and specific working conditions, and to establish a test and evaluation method for the accuracy of range of electric vehicles

Fuel consumption and emission performance from light-duty conventional/hybrid-electric vehicles over different cycles and real driving tests

Many studies have found that WLTC (The Worldwide harmonized Light vehicles Test Cycles) doesn’t accord well to real driving in different regions and it’s necessary to develop local test cycles. China announced its local test cycle in 2019: CLTC (China light-duty vehicle test cycle). To evaluate vehicle emission under different cycles, one conventional gasoline vehicle and its hybrid counterpart were tested on the chassis dynamometer following CLTC, WLTC, and RDE (Real Driving Emission). The fuel consumption between WLTC and RDE is at the same level. While for the conventional, CLTC fuel consumption is 8.41% higher than WLTC and for the hybrid, it’s 20.23% lower than WLTC. To get better vehicle fuel efficiency, vehicle application scenarios must be considered. Frequent re-start and longer warm-up time of the hybrid leads to high CO emission than the conventional. High engine speed could result in instantaneous CO spikes and with these spikes, 25% of the total CO could be emitted in less than 10 s. For the conventional, NOx emitted during engine warm-up occupied 85.39%, 87.02%, 43.06%, 31.98%, and 55.43% of the total NOx respectively for CLTC, WLTC and three RDE tests. NOx emitted from the hybrid is less than 10% of the conventional due to lower engine load and less fuel enrichment. Hybrid particle emission is under good control with the equipment of the gasoline particle filter, but the regeneration might increase thin particle exposure to the public. For most pollutants, CLTC doesn't close the gap between laboratory tests and real driving.

Performance and regulated gaseous emissions of a Euro 6 diesel vehicle with Lean NOx Trap at different ambient conditions: Sensitivity to the type of fuel

Three advanced biofuels, namely HVO (Hydrotreated Vegetable Oil), a glycerol-derived biofuel (Mo·bio) and biodiesel from oil industry wastes, were tested in a Euro 6 diesel vehicle equipped with a Lean NOx Trap under the worldwide harmonized light-duty vehicles test cycle (WLTC) at warm (24 °C) and cold (−7 °C) ambient temperature. HVO was tested pure, biodiesel was used both pure and blended at 20% (v/v) with a reference diesel fuel and Mo·bio was also blended with the diesel fuel at the same ratio. In order to analyse the sensitivity of the gaseous emissions and the aftertreatment efficiency to the type of fuel, emissions were measured upstream and downstream of the aftertreatment system and fuel-associated effects were isolated from those of the engine operating conditions (EGR rate, injection strategy and equivalence ratio). The energy consumption was not very different between fuels, although HVO led to a higher engine efficiency while biodiesel behaved oppositely at the low speed phase. Regarding NOx emissions, no differences were found between fuels while cold temperature led to higher NOx because of the lower EGR rate and the use of only high pressure EGR. Biodiesel and Mo·bio improved CO and THC engine-out emissions at warm temperature, but these compounds were deteriorated at low ambient conditions because of the poorer viscosity and volatility of these fuels. The DOC efficiency was higher for CO than for THC excepting the low speed phase, for which deposition of high molecular weight hydrocarbons could mask the results. The LNT efficiency was lower at cold conditions because of the high NOx engine-out emissions. Differences between fuels were only observed in the case of the DOC and during the engine warm-up period.

Energy management strategy to reduce pollutant emissions during the catalyst light-off of parallel hybrid vehicles

The transportation sector is a major contributor to both air pollution and greenhouse gas emissions. Hybrid electric vehicles can reduce fuel consumption and CO2 emissions by optimizing the energy management of the powertrain. The purpose of this study is to examine the trade-off between regulated pollutant emissions and hybrid powertrain efficiency. The thermal dynamics of the three-way catalyst are taken into account in order to optimize the light-off. Experimental campaigns are conducted on a spark-ignition engine to introduce simplified models for emissions, exhaust gas temperature, catalyst heat transfers and efficiency. These models are used to determine the optimal distribution of a power request between the thermal engine and the electric motor with three-dimensional dynamic programming and a weighted objective function. A pollution-centered scenario is compared with a consumption-centered scenario for various driving cycles. The optimal torque distribution for the emissions-centered scenario on the world harmonized light-duty vehicles test cycle shows an 8–33% decrease in pollutant emissions while the consumption remains stable (0.1% increase). The consistency of the results is analyzed with respect to the discretization parameters, driving cycle, electric motor and battery sizing, as well as emission and catalyst models. The control strategies are promising but will have to be adapted to online engine control where the driving cycle and the catalyst efficiency are uncertain.

Emission Factors Derived from 13 Euro 6b Light-Duty Vehicles Based on Laboratory and On-Road Measurements

Tailpipe emissions of a pool of 13 Euro 6b light-duty vehicles (eight diesel and five gasoline-powered) were measured over an extensive experimental campaign that included laboratory (chassis dynamometer), and on-road tests (using a portable emissions measurement system). The New European Driving Cycle (NEDC) and the Worldwide harmonised Light-duty vehicles Test Cycle (WLTC) were driven in the laboratory following standard and extended testing procedures (such as low temperatures, use of auxiliaries, modified speed trace). On-road tests were conducted in real traffic conditions, within and outside the boundary conditions of the regulated European Real-Driving Emissions (RDE) test. Nitrogen oxides (NOX), particle number (PN), carbon monoxide (CO), total hydrocarbons (HC), and carbon dioxide (CO2) emission factors were developed considering the whole cycles, their sub-cycles, and the first 300 s of each test to assess the cold start effect. Despite complying with the NEDC type approval NOX limit, diesel vehicles emitted, on average, over the WLTC and the RDE 2.1 and 6.7 times more than the standard limit, respectively. Diesel vehicles equipped with only a Lean NOX trap (LNT) averaged six and two times more emissions over the WLTC and the RDE, respectively, than diesel vehicles equipped with a selective catalytic reduction (SCR) catalyst. Gasoline vehicles with direct injection (GDI) emitted eight times more NOX than those with port fuel injection (PFI) on RDE tests. Large NOX emissions on the urban section were also recorded for GDIs (122 mg/km). Diesel particle filters were mounted on all diesel vehicles, resulting in low particle number emission (~1010 #/km) over all testing conditions including low temperature and high dynamicity. GDIs (~1012 #/km) and PFIs (~1011 #/km) had PN emissions that were, on average, two and one order of magnitude higher than for diesel vehicles, respectively, with significant contribution from the cold start. PFIs yielded high CO emission factors under high load operation reaching on average 2.2 g/km and 3.8 g/km on WLTC extra-high and RDE motorway, respectively. The average on-road CO2 emissions were ~33% and 41% higher than the declared CO2 emissions at type-approval for diesel and gasoline vehicles, respectively. The use of auxiliaries (AC and lights on) over the NEDC led to an increase of ~20% of CO2 emissions for both diesel and gasoline vehicles. Results for NOX, CO and CO2 were used to derive average on-road emission factors that are in good agreement with the emission factors proposed by the EMEP/EEA guidebook.

Analysis of the high instantaneous NOx emissions from Euro 6 diesel passenger cars under real driving conditions

In real-world driving, most Euro 5 and 6 diesel passenger cars exceed the nitrogen oxides (NOx) emission limits of type approval procedure. The emission factors of the fleet of Euro 6 vehicles show high variability, irrespective of the NOx control technology. This comprehensive study focused on the events of high instantaneous NOx emissions produced under real driving, to assess their impact on emission factors. Additionally, the relationships of these events with different parameters measured using portable emissions measurement system (PEMS) were determined. Three Euro 6b diesel passenger cars with exhaust gas recirculation (EGR), lean-burn NOx trap (LNT) and selective catalytic reduction (SCR) were tested based on the real driving emissions (RDE) regulation.The results show that high instantaneous NOx emissions represent a large amount of total NOx emissions, although they are produced in a small percentage of driving time. A theoretical constraint of these high NOx emissions could reduce emission factors by 30–82%. The emission of high instantaneous NOx emissions are related to characteristic speed modes of urban, rural and motorway sections, and are primarily produced in a narrow engine speed range of approximately 700 rpm. In general, the probability of producing high instantaneous NOx emissions increases as the engine speed, the exhaust gas temperature or the vehicle speed is increased. Finally, regarding driving severity, speed per positive acceleration (v⋅a+) observations above the maximum values of the new European driving cycle (NEDC) and the world-harmonized light-duty vehicle test cycle (WLTC), have a strong probability to yield high instantaneous NOx emissions. These findings could be useful in the design of low emission policies, optimization of NOx control strategies, and the improvement of micro/meso emission models.

Energy consumption and increased EV range evaluation through heat pump scenarios and low GWP refrigerants in the new test procedure WLTP

The aim of this work is to evaluate the cabin heating energy consumption and driving range for a battery electric vehicle. The vehicle was tested in climatic wind tunnel laboratory under Worldwide Harmonized Light-duty vehicle Test Cycle. A heating load model was established and used to predict the heating requirements of the vehicle in different climate conditions. Three different heat pump systems and five refrigerants are also investigated. Results show an error within 5% for the established heating load model. Compared with PTC heating, the heat pump systems lead to much lower energy consumption between 41% and 72% for different scenarios. Besides, 20% and 30% recirculation air can reduce the overall consumed energy by an average of 28.5% and 36.6%, respectively. Finally, the driving range of all the heat pump systems are much higher than that of PTC, which is between 14.2% and 31%.

Binomial multifractal features of worldwide harmonized light duty vehicles test cycle

Driving tests that have been performed for many years are not representative of actual vehicle operating conditions in terms of emissions and fuel consumption. This paper presents the research results of a new Worldwide harmonized Light duty Test Cycle (WLTC), that takes into account situations occurring in traffic inside and outside the city and on highways in Europe, India, Japan, Korea and USA. Conducted analysis demonstrated a multifractal nature of vehicle speed time signal, typical for he processes of asymmetric generalized multiplicative cascade.

Evaluation of the real-time de-NOx performance characteristics of a LNT-equipped Euro-6 diesel passenger car with various vehicle emissions certification cycles

Advanced nitrogen oxides (NOx) after-treatment systems for diesel cars are effectively reducing tailpipe NOx emissions in laboratory test cycles; however, some de-NOx systems showed limitation for passing environmental standards during real-world driving conditions. In this study, the NOx concentration of a lean NOx trap (LNT)-equipped diesel engine were investigated over various vehicle certification cycles. The LNT performance was compared to the new European driving cycle (NEDC), world-harmonized light-duty vehicle test cycle (WLTC), federal test procedure (FTP)-75, highway fuel economy test (HWFET), and US06. The real-time NOx concentration behaviors were tracked using NOx sensors at the engine-out and downstream of the LNT to determine the NOx storage and regeneration phase. The NOx conversion efficiencies were 36.3–71.7% of which reflecting the mode severity and cycle duration of the diesel engine. The tailpipe NOx emissions were 0.059 g/km during the NEDC which was within the Euro-6 emissions regulations. The NOx emissions in the WLTC, FTP-75, and US06 modes were approximately 1.9, 1.5, and 6.6 times higher than the NEDC due to the higher frequency of LNT purge and higher engine-out NOx formation. During the diesel particulate filter (DPF) regenerating stage in WLTC mode, tailpipe NOx emissions substantially increased by more than 8.8-fold. The exhaust gas recirculation (EGR) supply and lambda control scheme were closely related with strong NOx increment at de-NOx and de-PM processes.