Worldwide Harmonized Light Vehicles Test Cycle Research Articles

Optimal Energy Management for Hybrid Electric Vehicles Based on Dynamic Programming and Receding Horizon

Fuel consumption and emissions in parallel hybrid electric vehicles (HEVs) are directly linked to the way the load request to the wheels is managed between the internal combustion engine and the electric motor powered by the battery. A significant reduction in both consumption and emissions can be achieved by optimally controlling the power split on an entire driving mission (full horizon—FH). However, the entire driving path is often not predictable in real applications, hindering the fulfillment of the advantages gained through such an approach. An improvement can be achieved by exploiting more information available onboard, such as those derived from Advanced Driver Assistance Systems (ADAS) and vehicle connectivity (V2X). With this aim, the present work presents the design and verification, in a simulated environment, of an optimized controller for HEVs energy management, based on dynamic programming (DP) and receding horizon (RH) approaches. The control algorithm entails the partial knowledge of the driving mission, and its performance is assessed by evaluating fuel consumption related to a Worldwide harmonized Light vehicles Test Cycle (WLTC) under different control features (i.e., horizon length and update distance). The obtained results show a fuel consumption reduction comparable to that of the FH, with maximum drift from optimal consumption of less than 10%.

Effect of oxidation temperature on oxidation reactivity and nanostructure of particulate matter from a China VI GDI vehicle

Modern Gasoline Direct Injection (GDI) vehicles offered higher power output, improved fuel economy and reduced CO2 emissions compared with port fuel injection (PFI) vehicles. However, the particle number emission of GDI is larger than that of PFI and also higher than diesel vehicles equipped with diesel particle filter (DPF). This research sampled particle matter (PM) emitted from a China VI vehicle over the Worldwide harmonized Light vehicles Test Cycle (WLTC). The results of particle size distribution showed that ultra-fine particles in diameter below 23 nm take up majority of particle emissions. While with the oxidation temperature rising, the peak diameter of emitted particles migrated to larger section. The effect of oxidation temperature including interlayer spacing, fractal dimension, fringe length and tortuosity have been analyzed by TEM. The value of nano structural parameters increases slightly with the temperature increasing. Besides, the impact of volatile components was considered into the micromorphology and microstructure parameters of primary particles. After eliminating volatile materials, there is no presence of hollow carbon particles and all the three parameters including interlayer spacing, fringe length and fringe tortuosity showed an overall decrease. Better understanding nano structural parameters of PM under different oxidation temperatures can provide information to explain the potential impacts of particle emissions on human health and environment and the regeneration process of gasoline particle filter (GPF).

Generation of a Real-Life Battery Usage Pattern for Electrical Vehicle Application and Aging Comparison With the WLTC Profile

The process of determination of batteries lifespan for a specific application generally contains some aging tests. Most of the time, these tests used simplified power or current profiles designed specially to be as representative as possible of the reality. The use of a real profile could improve the reliability of the approach but needs to know how to select the typical profile from an available database. This article shows the methodology used to analyze a database of 10 electric vehicles monitored during 2 years. Different mathematical methods (Pearson and Spearman coefficient of correlation, Shannon entropy, principal component analysis, K-means, ...) were applied to sort the essential variables and classify the uses of the vehicle. Representative classes of uses were then gathered to constitute a profile used in aging tests. The aging results with this real-life type profile and with an adjusted WLTC (Worldwide Harmonized Light Vehicles Test Cycles) profile are presented and compared. The effectiveness of the use of the WLTC profile for aging tests in real life automotive application is shown.

A cost and time effective novel methodology to determine specific heat capacity of lithium-ion cells

A cost and time-effective novel method for determining the specific heat capacity of prismatic and pouch lithium-ion cells using a simple setup and easily available equipment is presented in this paper. Specific heat capacity is an important thermal parameter of lithium-ion cells which is not readily available or provided by the cell manufacturers. The results found in this work are compared with the calorimetrically determined values of the specific heat capacity and a maximum error of 5% and 1.4% have been found for the pouch and the prismatic cells, respectively. The minimum error in the specific heat capacity for the pouch and the prismatic cells are 0.7% and 0.1%, respectively. The thermal parameters obtained using this methodology have been used to model the surface temperature of a prismatic cell during the application of a dynamic pulsed power as well as New European Driving Cycle (NEDC) and Worldwide harmonized Light vehicles Test Cycle (WLTC) drive cycles-based power traces. The excellent matching of the measured and simulated cell’s surface temperature during both the NEDC and WLTC drive cycles demonstrates that the thermal parameters determined using this new method can be used to model the surface temperature of the cell.

Cooling system based on double-ball motor control valve

To realize eco-models based on (where 3R represents reducing, reusing, and recycling), both researchers and automobile development departments use controllable components to reduce vehicle fuel consumption and emissions. In this context, this paper presents the design of a double-ball motor control valve (DB-MCV). When compared with use of a traditional thermostat, use of the proposed valve in a Worldwide Harmonized Light Vehicles Test Cycle (WLTC) allows the coolant temperature to be controlled accurately as per the vehicle operating conditions, with control accuracy of ±1°C. Using this approach, the engine pre-heating time is reduced by 61 s, the total hydrocarbon (THC)) emission is reduced by 6.79%, the CO emission is reduced by 7.18%, and NOX emission is reduced by 4.84%. Under the same vehicle and working conditions, the engine fuel consumption is reduced by 2.31% on average. Under the cabin heating condition, the cabin temperature can be increased by 4.3°C, which improves the thermal comfort of the driver. When the vehicle is stopped after running at high speed and the engine is idling, the coolant temperature in the engine decreases rapidly, which reduces the risk of a hot dip occurring in the engine.

Analysis of real-driving emissions from light-duty gasoline vehicles: A comparison of different evaluation methods with considering cold-start emissions

Cold-start emissions from road vehicles are an important source of air pollution. However, how to evaluate them in the real driving emission (RDE) test is controversial. Although the Commission Regulation (EU) 2017/1154 and 2018/1832 successively adopt the moving averaging window (MAW) method and the cumulative averaging (CA) method to calculate the emission factors that include the cold-start emissions in the RDE tests, both the methods have been found to be flawed when processing the RDE data including cold-starts. To demonstrate the problem, the RDE test data from three light-duty gasoline vehicles were comparatively analyzed using the MAW method and the CA method. Results reveal that the MAW method unreasonably underestimates cold-start emissions in the urban and total trip emission evaluation, and the CA method tends to increase the inconsistency of the RDE evaluation results. Considering the inherently different characteristics between the cold-start emissions and the non-cold-start emissions, this paper proposes that the entire RDE test trip should be divided into a cold-start trip and a non-cold-start trip, and the cold-start emissions are evaluated by the CA method while the non-cold-start emissions are evaluated by the MAW method. Furthermore, the pollutant emission factors in the cold-start trip are corrected referring to the CO2 emissions emitted during the cold-start period of Worldwide harmonized Light vehicles Test Cycle (WLTC). Using this proposed approach, the aforementioned RDE tests were further analyzed and evaluated again. It is verified that the consistency of the test evaluation results in the RDE tests can be improved. The results of this study could be used to improve future emission regulations for the more reasonable evaluation of cold-start emissions in RDE tests.

Influence of Low Ambient Temperatures on the Exhaust Gas and Deposit Composition of Gasoline Engines

Abstract To comply with future emission regulations for internal combustion engines, system-related cold start conditions in short-distance traffic constitute a particular challenge. Under these conditions, pollutant emissions are seriously increased due to internal engine effects and unfavorable operating conditions of the exhaust aftertreatment systems. As a secondary effect, the composition of the exhaust gases has a considerable influence on the deposition of aerosols via different deposition mechanisms and on fouling processes of exhaust gas-carrying components. Also, the performance of exhaust gas aftertreatment systems may be affected disadvantageously. In this study, the exhaust gas and deposit composition of a turbocharged three-cylinder gasoline engine are examined in situ upstream of the catalytic converter at ambient and engine starting temperatures of −22 °C to 23 °C using a Fourier-transform infrared spectrometer and a particle spectrometer. For the cold start investigation, a modern gasoline engine with series engine periphery is used. In particular, the investigation of the behavior of deposits in the exhaust system of gasoline engines during cold start under dynamic driving conditions represents an extraordinary challenge due to an average lower soot concentration in the exhaust gas compared to diesel engines and so far has not been examined in this form. A novel sampling method allows ex situ analysis of formed deposits during a single driving cycle. Both, particle number concentration and the deposition rate are higher in the testing procedure of real driving emissions (RDEs) than in the inner city part of the worldwide harmonized light vehicles test cycle (WLTC). In addition, reduced ambient temperatures increase the amount of deposits, which consist predominantly of soot and to a minor fraction of volatile compounds. Although the primary particle size distributions of the deposited soot particles do not change when boundary conditions change, the degree of graphitization within the particles increases with the increasing exhaust gas temperature.

Error Analysis of the Normative Calculation Method of the Exhaust Emissions and Fuel Consumption in the Vehicles Fueled with Gaseous Fuels

The methodologies for calculating exhaust emissions and fuel consumption, which are given in the normative documents, do not take into account the fact that vehicles equipped with liquefied petroleum gas (LPG) or compressed natural gas (CNG) systems are fueled with petrol after a cold start. When calculating exhaust emissions and fuel consumption of LPG or CNG-powered vehicles, it is assumed that they result from the combustion of gaseous fuel only. This simplification leads to an incorrect determination of the emissions and fuel consumption values, as the formulas for calculating these values differ depending on the fuel type. This article presents the results of tests aimed at checking how that factor affects the value of emissions and fuel consumption calculated in the driving cycles used in the type-approval tests. In order to estimate the error resulting from this simplification, the tests of exhaust emissions and fuel consumption of a vehicle equipped with an LPG system were carried out. The tests were carried out on a chassis dynamometer in the worldwide harmonized light vehicles test cycle (WLTC) used in the type approval tests. In the tested vehicle, the CO, total hydrocarbons (THC), NOx and CO2 emissions calculated with the normative method were approx. 7% lower than the values calculated with the corrected method. For this reason, there is a need to develop a measurement method that allows for a separate analysis of the phase in which the vehicle is fueled with gasoline. This will allow the elimination of errors in the current normative method of calculating pollutant emissions from the exhaust system and fuel consumption of vehicles fueled with gaseous fuels.

Effects of engine restart strategy on particle number emissions from a hybrid electric vehicle equipped with a gasoline direct injection engine

Hybrid electric vehicle (HEV) tend to emit large amount of gaseous and particle emissions right after engine restart (ER). In this study, on-board particulate number (PN) measurement test and chassis dynamometer tests were conducted to analyze the effects of the ER combustion strategy on the gaseous and particle emission characteristics of a gasoline direct injection (GDI) HEV. The on-board PN measurement tests were conducted to examine the effect of a parameter sweep such as injection pressure, end of injection (EOI), spark timing of ER. It was measured by the pegasor particle sensor (PPS)-M, a device that measures the number of particles with a size from 23 nm to 25 μm, and the ES-582.1 module that can acquire electronic control unit (ECU) data. In the chassis dynamometer test, particle emissions, gaseous emissions and fuel economy of the reference case and the Combination Case 2 were compared and analyzed in the worldwide harmonized light vehicles test cycles (WLTC) mode test using Horiba, MEXA-ONE and MEXA-2000 solid particle counting system (SPCS). Reference case refers to a control strategy that does not touch anything in the vehicle's basic control strategy, and Combination Case 2 is the largest PN reduction case combined by calibrating the parameters. On-board PN measurement tests show that in reference case, ER PN accounted for about 70% of the total PN. Compared to the reference case, the sum of ER PN averages tended to decrease with higher injection pressure, advanced EOI, and retarded spark timing. The results of Combination Case 2 indicate that the sum of ER PN averages decreased by 88.7% compared to the reference case. In the WLTC mode test, THC, CO emissions and fuel economy were almost the same, and NOx was reduced by 85.6%. In both PPS and SPCS, the sum of ER PN average ratios decreased by 20%.

Characterization of Particle Emissions of Turbocharged Direct Injection Gasoline Engine in Transients and Hot Start Conditions

Reducing pollutant emissions, particularly soot particles emitted by internal combustion engines, is a major challenge for car manufacturers. In this paper, the experimental setup is a turbocharged three-cylinders gasoline direct injection engine installed on a HORIBA dynamic test driven by a HORIBA STARS computer. The particle-measuring device is a Pegasor Particles Sensor that measures the current carried by previously electrically charged particles. The hot engine stabilized tests, with lambda parameter lower or equal to one, have very low emission levels, unlike dynamic tests. As a consequence, the present paper deals with experiments in transient conditions. Unlike diesel engine, cycle tests show that particulate emissions vary widely. To understand the phenomenon, a simple transient was created and reproduced a hundred times in order to obtain enough data to analyze and compare these different tests. This transient starts from idle to reach the speed of 2000 r/min and 60 N.m in 5 s. To reach this point, it is necessary to stay in full load for about 3 s. The maximum deviations of particles reaches 85% with the standard deviation σ=18%. The cylinder pressure sensor shows significant variations at the very beginning of each transient, i.e., during the first 500 ms. This kind of result was observed for Worldwide harmonized Light vehicles Test Cycles (WLTC) with a maximum deviations of particles reaching 75% with σ=30%, on Real Drive Emissions Cycle (RDE) with a maximum deviations of particles reaching 45% with σ=22% and for a 300 s Mini-Cycle with a maximum deviations of particles reaching 70% with σ=17%. The Mini-cycle is made up of the five largest accelerations of the WLTP cycle. A complete analysis highlights the importance of filling the first engine cycles. This depends on the opening speed of the throttle, the position of the crankshaft at the beginning of the transient, and the acceleration of the first cycles. But, the NOx sensor shows very slight variations between each test. As a consequence, it appears that the variation of particles emissions is not only related to variation of equivalence ratio but with another setting, which may be the oil consumption. Finally, from these results, it is possible to determine a particle characterization function. It consists of two functions. The first one is the average of the emitted particles level which depends on the engine speed, engine acceleration, engine torque and torque acceleration. The second function, which corresponds to dynamic variations in emissions, mainly depends on oil consumption in the cylinder and on the combustion quality of the first transient engine cycles.

Measurement report: Distinct emissions and volatility distribution of intermediate-volatility organic compounds from on-road Chinese gasoline vehicles: implication of high secondary organic aerosol formation potential

Abstract. In the present work, we performed chassis dynamometer experiments to investigate the emissions and secondary organic aerosol (SOA) formation potential of intermediate-volatility organic compounds (IVOCs) from an on-road Chinese gasoline vehicle. High IVOC emission factors (EFs) and distinct volatility distribution were recognized. The IVOC EFs for the China V vehicle ranged from 12.1 to 226.3 mg per kilogram fuel, with a median value of 83.7 mg per kilogram fuel, which was higher than that from US vehicles. Besides, a large discrepancy in volatility distribution and chemical composition of IVOCs from Chinese gasoline vehicle exhaust was discovered, with larger contributions of B14–B16 compounds (retention time bins corresponding to C14-C16 n-alkanes) and a higher percentage of n-alkanes. Further we investigated the possible reasons that influence the IVOC EFs and volatility distribution and found that fuel type, starting mode, operating cycles and acceleration rates did have an impact on the IVOC EF. When using E10 (ethanol volume ratio of 10 %, v/v) as fuel, the IVOC EF of the tested vehicle was lower than that using commercial China standard V fuel. The average IVOC-to-THC (total hydrocarbon) ratios for gasoline-fueled and E10-fueled gasoline vehicles were 0.07±0.01 and 0.11±0.02, respectively. Cold-start operation had higher IVOC EFs than hot-start operation. The China Light-Duty Vehicle Test Cycle (CLTC) produced 70 % higher IVOCs than those from the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). We found that the tested vehicle emitted more IVOCs at lower acceleration rates, which leads to high EFs under CLTC. The only factor that may influence the volatility distribution and compound composition is the engine aftertreatment system, which has compound and volatility selectivity in exhaust purification. These distinct characteristics in EFs and volatility may result in higher SOA formation potential in China. Using published yield data and a surrogate equivalent method, we estimated SOA formation under different OA (organic aerosol) loading and NOx conditions. Results showed that under low- and high-NOx conditions at different OA loadings, IVOCs contributed more than 80 % of the predicted SOA. Furthermore, we built up a parameterization method to simply estimate the vehicular SOA based on our bottom-up measurement of VOCs (volatile organic compounds) and IVOCs, which would provide another dimension of information when considering the vehicular contribution to the ambient OA. Our results indicate that vehicular IVOCs contribute significantly to SOA, implying the importance of reducing IVOCs when making air pollution controlling policies in urban areas of China.

Research on ammonia emissions characteristics from light-duty gasoline vehicles

In this study, ammonia emissions characteristics of typical light-duty gasoline vehicles were obtained through laboratory vehicle bench test and combined with New European Driving Cycle (NEDC) condition and Worldwide Harmonized Light Vehicles Test Cycle (WLTC) condition. The influence of ambient temperature on ammonia emissions is mainly concentrated in the cold start stage. The influence of ambient temperature on ammonia emission is shown that the ammonia emissions of light-duty gasoline vehicles under ambient temperature conditions (14 and 23°C) are lower than those under low ambient temperature conditions (−7°C) and high ambient temperature conditions (35 and 40°C). The influence of TWC on ammonia emission is shown that ammonia is a by-product of the catalytic reduction reaction of conventional gas pollutants in the exhaust gas in the TWC. Under NEDC operating conditions and WLTC operating conditions, ammonia emissions after the catalyst are 45 times and 72 times that before the catalyst, respectively. In terms of ammonia emissions control strategy research, Pd/Rh combination can reduce NH3 formation more effectively than catalyst with a single Pd formula. Precise control of the engine's air-fuel ratio and combination with the optimized matched precious metal ratio TWC can effectively reduce ammonia emissions.

Triple-screw pumps for ICE cooling systems in the transportation sector

Recent EU Regulations have been pushing the transportation sector increasingly towards the reduction of primary harmful pollutants and CO2 emissions. In this context, the Internal Combustion Engine (ICE) cooling system is gaining a new technological interest. In fact, improvements on pump efficiency can significantly reduce its absorbed energy during real on-the-road operation. Typically, centrifugal pumps are adopted, but their efficiency is highly dependent on rotational speed, wasting energy during real operation, even if they are designed to have a very high efficiency at the design point. This study investigates the three screws pumps potentiality to substitute traditional centrifugal pumps in engine cooling applications. In fact, triple-screw pumps belong to positive displacement pumps, which have an efficiency ideally independent on rotational speed.A zero-dimensional mathematical model of this pump previously developed by the authors was improved, giving a specific focus on the mechanical efficiency of the pump. The validation of the model resulted in a good agreement with experimental results. The model has been used to design a pump for an IVECO F1C diesel engine. The energy requested to drive the pump over a Worldwide Harmonized Light Vehicles Test Cycle (WLTC) has been calculated and compared with that of the traditional existing centrifugal pump. Results show that the electrically actuated triple screw pump allows to reduce the energy of about 14 %.

Particle Swarm Optimization and Real-Road/Driving-Cycle Analysis Based Powertrain System Design for Dual Motor Coupling Electric Vehicle

In this study, a planetary gear based dual motor coupling electric vehicle is proposed, which achieves higher system efficiency by enabling motor working under high operating efficiency area. Firstly, the dynamic characteristics of the proposed configuration are analyzed and the reasonable working modes are established. Secondly, the optimal dual motor parameters are derived according to the statistical analysis on the typical driving conditions and the collected real road driving data. Especially, the optimal parameters of planetary gear and final transmission ratio are obtained using particle swarm optimization algorithm. Finally, based on the developed mode shift algorithm, the dual motor coupling full vehicle model is developed and the vehicle performance is analyzed using MATLAB/Simulink. For the UDDS (Urban Dynamometer Driving Schedule) driving cycle, it is seen from the simulation results of motor operating points that the proposed dual motor configuration is mostly operated under the high efficiency range, and the power consumption is significantly reduced by 7.6% compared with the single motor configuration. For the NEDC (New European Driving Cycle), WLTC (Worldwide Harmonized Light Vehicles Test Cycle) and real road driving conditions, the proposed dual motor configuration also achieves system efficiency improvement of 5.0%~16.3%, which confirms the validity of the proposed configuration and its corresponding parameter matching and control algorithm development.

NOx sensor cross sensitivity model and simultaneous prediction of NOx and NH3 slip from automotive catalytic converters under real driving conditions

This work presents the development of a model to capture the NOx sensors cross sensitivity behavior based on [Formula: see text] sensor cell temperature, as well as a model do predict the slip of the NOx and NH3 after the SCR catalyst, as a way to reduce the error in the exhaust emissions estimation needed for feedback SCR control strategies. The emissions prediction model is based on the different cross sensitivity behavior of two distinct NOx sensors. The proposed models were tested and compared on a fully instrumented engine test bench when applied in a Worldwide harmonized Light vehicles Test Cycle (WLTC) and a full map cycle. As a result, the proposed model showed for NOx sensors cross sensitivity estimation an overall improvement of 34.8% for sensor 1 and 31.0% for sensor 2, and in terms of emissions prediction an overall improvement of 36.3% for NOx and 45.5% for NH3 slip.

Effect of the exhaust thermal insulation on the engine efficiency and the exhaust temperature under transient conditions

As well as new advances in the after-treatment systems are required to achieve the new pollutant emission requirements, new designs of the exhaust line can be considered in order to increase the engine efficiency and the after-treatment effectiveness. In the present work, a one-dimensional gas dynamic model has been used to carry out a simulation study comparing several exhaust insulation solutions. This solutions include the insulation of the exhaust ports, the exhaust manifold, the internal surface of the turbine volute, the turbine external housing, as well as different combinations of these solutions. A transient analysis has been done in order to evaluate the increment in the exhaust gases temperature, fuel economy and pollutant emission levels over the WLTC (Worldwide harmonized Light vehicles Test Cycle) at three different temperature conditions. As a conclusion, a 12% increment in the turbine outlet gas enthalpy can be achieved by insulating both the exhausts ports and the exhaust manifold. Moreover, more than 30% less pollutant emissions are released to the environment with this setup.

Integrated Plant and Control Design of a Continuously Variable Transmission

This paper presents an optimization framework to design the components and the controller of a Continuously Variable Transmission (CVT) in an integrated manner. Specifically, we aim at reducing the mass of the transmission and the leakage losses that occur in the system. To do so, we first formulate the joint plant and control design problem including the corresponding objectives and constraints. Thereafter, we propose a proportional integral structure for the design of the CVT ratio control. The combined plant and control design problem is formulated as a nonlinear multi-objective optimization problem, and is simultaneously solved using an interior point optimization method. We evaluate the obtained design on the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) as well as on more aggressive driving scenarios, and demonstrate that the optimized CVT design is always capable of realizing the required driving performance. Additionally, we study the impact of the plant design parameters on the control performance by analyzing the coupling strength between the subproblems. Thereby, the pulley radius is found to have the strongest influence in the resulting leakage losses that occur at the variator level. Finally, leveraging the presented design framework, we show that up to 13% and 18% reduction in the CVT variator mass and on leakage losses, respectively, can be achieved without compromising the desired ratio trajectory over a representative dynamic driving cycle.

Experimental evaluation of on-road fuel consumption for a 2.2 L diesel-fueled vehicle at two driving routes

In this study, we investigated the RDE (real driving emissions) test with a diesel passenger vehicle and two RDE driving routes. We then experimentally analyzed the implications for fuel consumption of a 2.2L diesel-fueled vehicle. First, we found that the weighting factor, which is the product of the carbon dioxide average value from the MAW (moving average window) analysis, results in real-road fuel consumption measurement that are closer to the WLTC (worldwide harmonized light vehicles test cycles) measurement results. Therefore, we ignored the weighting factor of the WLTC and used a new weighting factor of distance instead. In order to determine the influence of each factor on the fuel efficiency, we analyzed the carbon-dioxide emission for the operation of additional equipment. And OBD values were used to develop correction equations to compensate for vehicle driving regions where GPS data was not measured in the test route. When using the weighting factor based on the WLTC standard, the weighting factor based on distance was introduced to calculate the fuel consumption in this study.

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.

Impact of altitude on the real driving emission (RDE) results calculated in accordance to moving averaging window (MAW) method

Over half of the high altitude RDE tests failed to pass trip validity verification. To find out the reason and proper solution, vehicles were tested over The Worldwide harmonized Light vehicles Test Cycles (WLTC)/RDE at various altitudes and RDE tests were calculated using different WLTC reference data. Generally, the higher the altitude, the lower the vehicle CO2 emission and CO2 emission of naturally aspirated test vehicle has a linear correlation with altitudes: every 1000 m the altitude rise, WLTC CO2 emission will decrease 5.31%. The reasons for urban trip validity verification failure are the intensity of test cycles, different calculation methods and lower air resistance at high altitude, while for rural/motorway trip validity verification failure, lower air resistance is the only reason. Both high altitude reference data and sea level reference data with coefficients are plausible for high altitude RDE calculation. At 2400 m, the coefficients are 0.98, 0.91 and 0.86 for urban, rural and motorway respectively, but the calculation of the coefficients needs to be verified by more study. No correlation was found between reference data and RDE results.