Start Emissions Research Articles

The problem of cold start emissions from vehicles

The problem of cold start emissions from vehicles

Co3O4 as an efficient passive NOx adsorber for emission control during cold-start of diesel engines

The Co3O4 nanoparticles, dominated by a catalytically active (110) lattice plane, were synthesized as a low-temperature NOx adsorbent to control the cold start emissions from vehicles. These nanoparticles boast a substantial quantity of active chemisorbed oxygen and lattice oxygen, which exhibited a NOx uptake capacity commensurate with Pd/SSZ-13 at 100 °C. The primary NOx release temperature falls within a temperature range of 200-350 °C, making it perfectly suitable for diesel engines. The characterization results demonstrate that chemisorbed oxygen facilitate nitro/nitrites intermediates formation, contributing to the NOx storage at 100 °C, while the nitrites begin to decompose within the 150-200 ºC range. Fortunately, lattice oxygen likely becomes involved in the activation of nitrites into more stable nitrate within this particular temperature range. The concurrent processes of nitrites decomposition and its conversion to nitrates results in a minimal NOx release between the temperatures of 150–200 °C. The nitrate formed via lattice oxygen mainly induces the NOx to be released as NO2 within a temperature range of 200–350 °C, which is advantageous in enhancing the NOx activity of downstream NH3-SCR catalysts, by boosting the fast SCR reaction pathway. Thanks to its low cost, considerable NOx absorption capacity, and optimal release temperature, Co3O4 demonstrates potential as an effective material for PNA applications.

Prediction of cold start emissions for hybrid electric vehicles based on genetic algorithms and neural networks

The emission of hybrid electric vehicles deteriorates during cold start, and it is a cost-effective method to reduce pollutant emissions during cold start of hybrid electric vehicles through energy management strategies. The development of energy management strategies for hybrid electric vehicle requires an accurate cold-start emissions model. However, traditional cold-start emission models based on statistics and experience are difficult to achieve satisfactory prediction accuracy, and require a lot of experimental cost and time. The use of neural networks for cold start emission prediction of hybrid electric vehicles has been widely used because of its low cost and high prediction accuracy. In this paper, the genetic algorithm is used to optimize the weights and thresholds of the neural network, and a neural network cold-start emission prediction model for hybrid electric vehicles is built. We trained the neural network using the high temperature (40 °C), normal temperature (23 °C) and low temperature (−20 °C) cold start data of hybrid vehicles obtained in the World Light Vehicle Test Code (WLTC), studied the cold start prediction results under the different cold start temperature, studied the cold start prediction results under the different input parameters, studied the cold start prediction results of the neural network optimized by the genetic algorithm. Under different input parameters and cold start temperature, the GA-BP algorithm can accurately predict the emissions of carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (THC), nitrogen oxides (NOx) and particulate matter number (PN) under hybrid electric vehicles.

Updating emission inventories for vehicular organic gases: Indications from cold-start and temperature effects on advanced technology cars

How would the organic gas emission inventories of future urban vehicles change with new features of advanced technology cars? Here, volatile organic compounds (VOCs) and intermediate volatile organic compounds (IVOCs) from a fleet of Chinese light-duty gasoline vehicles (LDGVs) were characterized by chassis dynamometer experiments to grasp the key factors affecting future inventory accuracy. Subsequently, the VOC and IVOC emissions of LDGVs in Beijing, China, from 2020 to 2035, were calculated and the spatial-temporal variations were recognized under a scenario of fleet renewal. With the tightening of emission standards (ESs), cold start contributed a larger fraction of the total unified cycle VOC emissions due to the imbalanced emission reductions between operating conditions. It took 757.47 ± 337.75 km of hot running to equal one cold-start VOC emission for the latest certified vehicles. Therefore, the future tailpipe VOC emissions would be highly dependent on discrete cold start events rather than traffic flows. By contrast, the equivalent distance was shorter and more stable for IVOCs, with an average of 8.69 ± 4.59 km across the ESs, suggesting insufficient controls. Furthermore, there were log-linear relationships between temperatures and cold-start emissions, and the gasoline direct-injection vehicles performed better adaptability under low temperatures. In the updated emission inventories, the VOC emissions were more effectively reduced than the IVOC emissions. The start emissions of VOCs were estimated to be increasingly dominant, especially in wintertime. By winter 2035, the contribution of VOC start emissions could reach 98.98 % in Beijing, while the fraction of IVOC start emissions would decrease to 59.23 %. Spatially allocation showed that the high emission regions of tailpipe organic gases from LDGVs have transferred from road networks to regions of intense human activities. Our results provide new insights into tailpipe organic gas emissions of gasoline vehicles, and can support future emission inventories and refined assessment of air quality and human health risk.

Impacts on real-world extra cold start emissions: Fuel injection, powertrain, aftertreatment and ambient temperature

Vehicles emit substantial amounts of pollutants during start periods. Engine starts mainly occur in urban areas, causing serious harm to humans. To investigate the impacts on extra cold start emissions (ECSEs), eleven China 6 vehicles with various control technologies (fuel injection, powertrain, and aftertreatment) were monitored with a portable emission measurement system (PEMS) at different temperatures. For conventional internal combustion engine vehicles (ICEVs), the average ECSEs of CO2 increased by 24%, while the average ECSEs of NOx and particle number (PN) decreased by 38% and 39%, respectively, with air conditioning (AC) on. Gasoline direct injection (GDI) vehicles had 5% lower CO2 ECSEs, but 261% higher NOx ECSEs and 318% higher PN ECSEs than port fuel injection (PFI) vehicles at 23 °C. The average PN ECSEs were significantly reduced by gasoline particle filters (GPFs). The GPF filtration efficiency was higher in GDI than PFI vehicles due to particle size distribution. Hybrid electric vehicles (HEVs) generated excessive PN extra start emissions (ESEs), resulting in a 518% increase compared to ICEVs. The start times of the GDI-engine HEV accounted for 11% of the whole test time, but the proportion of PN ESEs relative to total emissions were 23%. Linear simulation based on the decrease in ECSEs with increasing temperature underestimated the PN ECSEs from PFI and GDI vehicles by 39% and 21%, respectively. For ICEVs, CO ECSEs varied with temperature in a U shape with a minimum at 27 °C; NOx ECSEs decreased as ambient temperature increased; PFI vehicles generated more PN ECSEs at 32 °C than GDI vehicles, stressing the significance of ECSEs at high temperature. These results are useful for improving emission models and assessing air pollution exposure in urban aeras.

Quantifying start emissions and impact of reducing cold and warm starts for gasoline and hybrid vehicles

In this study, a portable emissions measurement system (PEMS) was used to measure trip emissions of a gasoline vehicle (2020 Hyundai Tucson Preferred) and a hybrid vehicle (2020 Ford Fusion Hybrid Titanium) under various soak times (12 h–1 min) along two driving routes in Toronto, Canada (highway and city core). A new method was proposed to identify start emissions in a PEMS test, employing confidence intervals (CIs) of hot-running emission rates, and distributions of hot-running coolant and catalyst temperatures. In addition, GPS data reflecting one-week of travel for 82 drivers in Toronto were used to quantify the contributions of start emissions under realistic trip schedules and to estimate the benefits of reducing cold and warm starts. In Toronto, over 95% of the trips have a soak time over 1 h, and over 33% of the trips are within 5 km. Compared to the Tucson, the Fusion Hybrid generates approximately 43.4% less carbon dioxide (CO2) and 77.7% less nitrogen oxides (NOx), but 183.6% more carbon monoxide (CO) and 15.8% more ultrafine particles (measured in particle number, PN), on a representative Toronto drive schedule. For soak times greater than 12 h and trip distance less than 5 km, the contributions of starts to total trip emissions for CO2, CO, NOx, and PN are in the ranges of 13.4%–70.0%, 93.5%–99.9%, 22.3%–73.9%, and 80.3%–99.3%, respectively, for the Tucson. For the Fusion Hybrid, these contributions are in the ranges of 31.4%–95.6%, 25.1%–73.2%, 58.7%–95.9%, and 25.6%–87.7%. With engine and catalyst preheating, total trip emissions for CO2, CO, NOx, and PN decrease on average by 5.1%, 81.3%, 20.2%, and 48.1%, respectively, for the Tucson. For the Fusion Hybrid, these reductions are 10.4%, 16.3%, 40.8%, and 7.9%.

An Experimental and Computational Study on Triple Injection Strategies to Reduce Cold Start Diesel Engine Emissions

Abstract The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions.

Thermal management of catalytic converter with heat pipe embedded in thermal energy storage to reduce cold start emissions

ABSTRACT The Thermal Energy Storage (TES) System aids in improving the cold start efficiency of the catalytic converter (CC). To further improve the TES and CC performance, loop heat pipes embedded into the PCM, TES unit are presented. For evaluation, three cases are considered: Case 1; CC without TES, Case 2; CC with TES, Case 3; CC with a heat pipe embedded in PCM TES. Mg70Zn24.9Al5.1 is used as PCM and paraffin oil as the working fluid for the heat pipe. Three 30 minute transient cycles with idle events in between were run, with the engine soaking for 30 minutes at ambient conditions with varied loads (0 to 100%) at 2000 rpm. Heat storage and release cycles were run for each load condition. Average warm-up HC, NOx and CO conversion efficiency improvement of 45–85% with Case 3, 35–62% with Case 2 compared to Case 1 were observed. Heat storage time was observed to be lower by ~ 35% for Case 3 while the heat retention time was observed to be better for Case 2 by ~44%. System efficiency and effectiveness were found to be better up to 14% and ~0.2 with Case 3 compared to Case 2. Overall Case 3 showed better performance with some penalty on the heat retention time compared Case 2.

Evaluation of Advanced Diesel Particulate Filter Concepts for Post Euro VI Heavy-Duty Diesel Applications

The European Commission (EC) is in the process of finalizing the proposal for the upcoming legislative stage for light- and heavy-duty vehicles. The emission performance over extended operating conditions is under consideration. Furthermore, a tightening of the Solid Particle Number (SPN) limits with a parallel shift of the lowest detectable size from 23 to 10 nm has been suggested. This paper investigates the SPN emission performance of a Euro VI step E HDV and the potential offered by an advanced Diesel Particulate Filter (DPF) to meet the upcoming regulations. Cold start emissions at clean DPF state were found to be as high as 1.3 × 1012 #/kWh, while passive regeneration events could lead to hot start emissions of 3 × 1011 #/kWh. Improvements in the filtration efficiencies at clean state, similar to those offered by the advanced DPF (>99%), will be needed to tackle these operating conditions. The measurements also revealed the formation of 10 nm SPN in the Selective Catalytic Reduction (SCR) system, at a rate of ~1.2 × 1011 #/kWh. These levels lie above the proposed limit of 1011 #/kWh, highlighting the need to also control these non-volatile nanosized particles.

Comprehensive Control Strategy of Fuel Consumption and Emissions Incorporating the Catalyst Temperature for PHEVs Based on DRL

PHEVs (plug-in hybrid electric vehicles) equipped with diesel engines have multiple model transitions in the driving cycle for their particular structure. The high frequency of start–stop of a diesel engine will increase fuel consumption and reduce the catalytic efficiency of SCR (Selective Catalyst Reduction) catalysts, which will increase cold start emissions. For comprehensive optimization of fuel consumption and emissions, an optimal control strategy of PHEVs that originated from the PER-TD3 algorithm based on DRL (deep reinforcement learning) is proposed in this paper. The priority of samples is assigned with greater sampling weight for high learning efficiency. Experimental results are compared with those of the DP (dynamic programming)-based strategy in HIL (hardware in loop) equipment. The engine fuel consumption and NOX emissions were 2.477 L/100 km and 0.2008 g/km, nearly 94.1% and 90.1% of those of the DP-based control strategy. By contrast, the fuel consumption and NOx of DDPG (Deep Deterministic Policy Gradient)-based and TD3(Twin Delayed Deep Deterministic Policy Gradient) -based control strategy were 2.557, 0.2078, 2.509, and 0.2023, respectively. By comparative results, we can see that the comprehensive control strategy of PHEVs based on the PER-TD3 algorithm we proposed can achieve better performance with comparison to TD3-based and DDPG-based, which is the state-of-the-art strategy in DRL. The HIL-based experimental results prove the effectiveness and real-time potential of the proposed control strategy.

Enhancement of catalytic converter performance to reduce cold start emissions with thermal energy storage – An experimental study

A “Thermal Energy Storage” (TES) system can assist in solving the cold start emission problem associated with the catalytic converter. “Phase change materials” (PCMs) can be used in the TES system to absorb heat from the exhaust gases, liquefy it and store it as latent heat. This makes it possible to store the exhaust heat during the engine running conditions and to release it on the catalyst substrate during the off-engine and low temperature start. A catalytic converter is integrated with a TES unit with Mg70Zn24.9Al5.1 as PCM having melting point in range of 310 °C & 157 kJ/kg as heat of fusion. This paper presents Experimental investigation of Catalytic Converter for exhaust temperature, conversion efficiency with and without TES unit. The investigation includes the heat storage and retention time during engine operation. Test cycle of 150 min with each load were run including idle events in between at 2000 rpm for different load conditions. Results showcased maximum average conversion efficiency improvement for 60 %, 53 % and 30 % for HC, NOx and CO respectively at No load condition during cold start. Heat Retention time was found higher for high loads, 100 % & 75 % load temperature was observed to remain above 100 0C for nearly 350 min.

A bottom-up modeling approach to quantify cold start emissions from urban road traffic

Cold start emissions, which are released during the first minutes of driving after the vehicle engine is started, may contribute significantly to the urban road traffic emissions. Implementation of bottom-up approaches for emission quantification in urban context is crucial to address the distribution of pollution with fine temporal and spatial resolution and to establish local mitigation measures and plans. In this research a modeling approach to quantify cold start excess emissions from road transport with fine spatial resolution is proposed and applied. In combination with transportation modeling, a new module has been developed to estimate cold start emissions at road segment level and for a trip, while preserving information on Origin-Destination of the trips contributing to those emissions. The methodology was applied to Coimbra case study allowing spatial analysis of cold start emissions in the urban context. The frequency distribution and summary statistics for road segments are provided focusing on different types of roads and seasonal variations. High contribution of cold start emissions is demonstrated with median values above 70% for carbon monoxide and hydrocarbons at local roads, where most people leave or work. The methodology applied in this work highlights the importance of cold start emission quantification for traffic pollution studies.

Comprehensive kinetic model of a three-way catalyst for stoichiometric natural gas engines: Experiments and simulation

BackgroundKinetic modeling is an important technique for designing and optimizing automotive exhaust gas aftertreatment systems. However, few kinetic models can simultaneously predict the main pollutant removal and byproduct formation on three-way catalysts for stoichiometric natural gas engines. Therefore, further development of the TWC model was needed to address such issues. MethodsIn this study, a detailed global kinetic model for natural gas engines was developed by extending the classic TWC model by combining the investigation of reaction pathways and light-off experiments over a wide range of conditions. Significant findingsWith the help of a gradually simplified light-off experiment, the main side reactions between NO and CO/H2/O2 to form NH3/N2O/NO2 were well defined. Adding all observed reactions into the classic model, the extended kinetic model can capture all the experimental phenomena under a wide range of operating conditions in laboratory light-off tests. Importantly, this model can also describe the light-off phenomena of aged samples when aging factors are used. Apart from predicting reactor-scale phenomena, the extended model above describes and predicts the cold start emission under cold WHTC. This study provides a feasible and straightforward method to build a global kinetic model covering full-scale laboratory conditions to actual operating conditions.

Simulation of liquid meniscus formation in the ionic liquid electrospray process

Though tremendous efforts have been made to investigate electrospray, some aspects, such as the evolution of the menisci on the micropores of porous emitter tips and the transient response of the meniscus during the polarity alternation, need to be further understood. This paper presents a computation fluid dynamics (CFD) model to describe the meniscus formation in the ionic liquid electrospray process. The CFD model, based on the Taylor–Melcher leaky dielectric fluid theory and the volume of fluid (VOF) method, is validated by experiments. The evolution of the meniscus on the basis of a micropore is presented using two typical ionic liquids, EMI-BF4 and EMI-Im. The influences of the pore size, flow rate and applied voltage on the formation of the meniscus have been studied. Results show that a larger pore is more likely to start emission, and the time consumed for liquid meniscus formation decreases with increasing applied voltage and flow rate. Further, it is found that alternation of polarity does not destroy the structure of the meniscus but retards the formation process, and a faster polarity alteration leads to a shorter delay in meniscus formation time.

Reproducibility of the 10-nm Solid Particle Number Methodology for Light-Duty Vehicles Exhaust Measurements

Many countries worldwide have introduced a limit for solid particles larger than 23 nm for the type approval of vehicles before their circulation in the market. However, for some vehicles, in particular for port fuel injection engines (gasoline and gas engines) a high fraction of particles resides below 23 nm. For this reason, a methodology for counting solid particles larger than 10 nm was developed in the Particle Measurement Programme (PMP) group of the United Nations Economic Commission for Europe (UNECE). There are no studies assessing the reproducibility of the new methodology across different laboratories. In this study we compared the reproducibility of the new 10 nm methodology to the current 23 nm methodology. A light-duty gasoline direct injection vehicle and two reference solid particle number measurement systems were circulated in seven European and two Asian laboratories which were also measuring with their own systems fulfilling the current 23 nm methodology. The hot and cold start emission of the vehicle covered a range of 1 to 15 × 1012 #/km with the ratio of sub-23 nm particles to the >23 nm emissions being 10–50%. In most cases the differences between the three measurement systems were ±10%. In general, the reproducibility of the new methodology was at the same levels (around 14%) as with the current methodology (on average 17%).

From shifting gears to changing modes: The impact of driver inputs on plug-in hybrid electric vehicle energy use & emissions

This study measures the energy use and emission impacts of driver-induced changes to drivetrain configurations, known as drive modes. Drive modes allow drivers to alter their vehicles’ operating characteristics including propulsion energy sources, responsiveness of the steering wheel/accelerator pedal, etc. Plug-in Hybrid Electric Vehicles (PHEVs) can use energy from a combination of a battery and a fuel source to propel themselves, so drive modes that can shift vehicle propulsion power sources can directly impact energy usage and emissions in these vehicles. This study examines the use of drive modes in PHEVs. We use empirical, on-road vehicle data to explore whether drivers are using drive modes as intended by vehicle manufacturers and to develop a regression model and engine start analysis to quantify the impact of mode usage on PHEV energy efficiency and emissions. We find that incorrect use of drive modes leads to a 15–30% increase in energy usage and higher engine start emissions.

Review of Vehicle Engine Efficiency and Emissions

<div class="section abstract"><div class="htmlview paragraph">This review covers advances in regulations and technologies in the past year in the field of vehicular emissions. We cover major developments towards reducing criteria pollutants and greenhouse gas emissions from both light- and heavy-duty vehicles and off-road machinery. To suggest that the transportation is transforming rapidly is an understatement, and many changes have happened already since our review last year [<span class="xref">1</span>]. Notably, the US and Europe revised the CO<sub>2</sub> standards for light-duty vehicles and electrification mandates were introduced in various regions of the world. These have accelerated plans to introduce electrified powertrains, which include hybrids and pure electric vehicles. However, a full transformation to electric vehicles and the required grid decarbonization will take time, and policy makers are accordingly also tightening criteria pollutant standards for internal combustion engines. California has published the Advanced Clean Cars II standards and Europe has held various workshops outlining the core elements of future Euro 7 regulations. These will likely be the last major regulations for criteria pollutants, and compliant vehicles will likely be zero-impact emitting, that is with tailpipe emissions at or lower than the ambient concentrations. Meeting these regulations will require adoption of several advanced engine and emission control technologies which we discuss here. Emphasis will be on reducing cold start emissions, likely requiring active thermal management strategies. The challenge will be to lower criteria pollutants while also reducing fuel consumption, and we review some approaches being considered. The story is similar for heavy-duty vehicles, where meeting California’s Low NOx regulations and Euro VII scenarios require significantly improved engine controls and after-treatment systems. New system solutions and hardware additions show a pathway to meeting the regulations, although we caution that much more work is needed ahead to achieve the reductions over extended durability limits and with healthy engineering margins. We also review the impact of alternative fuels on reducing well-to-wheels (WTW) greenhouse gas emissions, along with recommendations to continue improving market fuel quality to reduce negative impact on criteria pollutants. Finally, while this paper does not intend to provide a detailed review of battery electric or fuel cell vehicle technology, we touch upon a few studies which discuss the outlook of powertrain diversification from a total cost of ownership and greenhouse gas reduction perspective.</div></div>

Study on pollutant emission characteristics of different types of diesel vehicles during actual road cold start

The current regulations of heavy-duty vehicles in China do not include the emissions in the cold start stage into the overall emission evaluation. However, the speed of heavy-duty diesel vehicles in the cold start stage is often low and the proportion of idle-conditions is large, resulting in the difference between the actual test results and evaluation results of emissions. Therefore, in order to accurately evaluate the impact of emission during cold start on the overall emission, in this study, the OBS-ONE portable vehicle emission test equipment was used to test the emission of three representative heavy-duty diesel vehicles with different types under actual road driving conditions, and the cumulative averaging (CA) method was adopted to calculate and analyze the test emission data.Firstly, the cold start emission of different types of heavy-duty vehicles was evaluated. The results show that the contribution rate of pollutant emission in the cold start stage is high, in which NOx emission accounts for 40–90% of the whole trip. It was unreasonable for regulations to exclude data in the cold start stage. The cold start duration of vehicle A is nearly 300 s longer than that of vehicle C, however, the NOx and PN emission factors of vehicle A are nearly 10 times and 100 times smaller than that of vehicle C at the cold start stage respectively. The cold start duration, fuel consumption and the emission factors in cold start stage of different types of heavy-duty diesel vehicles do not have a unified law. Secondly, the emission characteristics and differences of different types of heavy-duty vehicles are studied at the instantaneous level, and the internal mechanism causing the emission differences is explored and revealed. In the cold stage, CO2 emission shows a good correlation with the fuel consumption. CO, NOx emissions show a good correlation with the fuel consumption when the engine and post-treatment temperature are low, and CO and NOx emissions decrease with the increase of engine and post-treatment temperature. PN emissions are mainly related to the engine working state. Finally, the influence of dynamic parameters v·a and RPA on pollutant emission was analyzed. The results show that driving force is an important factor affecting CO2 emission, and RPA has no obvious correlation with emission at cold start stage.

Investigating Particulate and Nitrogen Oxides Emissions of a Plug-In Hybrid Electric Vehicle for a Real-World Driving Scenario

Plug-in hybrid electric vehicles (PHEVs) show a high pollutant emission variability that strongly depends on the operating conditions of the internal combustion engine. Additionally, studies indicate that driving situations outside of the real driving emissions boundary conditions can lead to substantial pollutant emission increases. The objective of this study is to measure and analyze the particulate number (PN) and nitrogen oxides (NOx) emissions of a Euro 6 PHEV for a selected real-world driving test route in the Stuttgart metropolitan area. For this purpose, the vehicle is set out with multiple measurement devices to monitor vehicle internal and external parameters. Particle distribution results show an overall uniform pattern, which allows a comparative analysis of the different test scenarios on the basis of the PN concentration. While the trip-average PN emissions are in good agreement, transient effects during highway driving can substantially increase emissions, whereas the fuel consumption does not necessarily increase in such situations. PN measurements including ultrafine particles (UFP) show a significant increase in urban emissions due to higher cold start emission peaks. Additionally, low ambient temperatures raise the uncertainty of NOx and PN cold start emissions. With regard to future emission regulations, which claim that vehicles need to be as clean as possible in all driving situations, PHEV emission investigations for further situations outside of the current legislations are required.

Research on the impact of new OBD diagnostic items on the emission of China 6 light-duty vehicles

The new diagnostic items such as fuel system, VVT and cold start emission reduction strategy are tested for several vehicles meeting the requirements of the China 6 emission standards of light-duty vehicles. The test results show that the fuel system fault will increase the emissions of NMHC, NOx, CO and other pollutants by 0.7-7.5 times, and the emissions of lean mixture, rich mixture and uneven cylinder to cylinder faults will increase to different degrees; VVT fault will increase NMHC and CO emissions by 1.2-2.9 times and NOx by 1.6-6.1 times; The failure of cold start emission reduction strategy will increase NMHC, NOx and CO emissions by 4.2-9.0 times and NOx by 2.1-2.2 times; It is necessary to strengthen the monitoring of these diagnostic items and tighten the requirements in the future emission standards.