Light-duty Vehicle Emissions Research Articles

Evaluating real-world emissions of light-duty gasoline vehicles with deactivated three-way catalyst converters

Three-way catalyst (TWC) converter is one of the most important after-treatment device for modern light-duty gasoline vehicles (LDGVs), which can efficiently control exhaust emissions of carbon monoxide (CO), total hydrocarbons (THC) and nitrogen oxides (NOX). Nevertheless, a considerable part of in-use taxis in Beijing would operate with TWC purposely removed, which have been indicated by vehicular on-board diagnostic (OBD) systems. In light of high vehicle-use intensity for taxis, we recruited three China 4 non-TWC taxis and three China 4 normal taxis in a comparative experimental test by using a portable emissions measurement system (PEMS). The results indicated that non-TWC taxis emitted significantly higher emissions of air pollutants than normal taxis with TWC functioning. For example, average emission factors of non-TWC vehicles were comparable to emission levels of China 1 LDGVs measured in previous studies. By contrast, emissions from normal China 4 taxis were all below China 4 emission limits. Furthermore, an operating mode binning method and a micro-trip approach have been employed to link vehicle emissions with driving conditions. For non-TWC taxis, we identified strong correlations of all pollutant categories between emission factors and average speed. However, such correlations for normal taxis were less strong, in particular for CO and THC emissions that were hardly sensitive to speed changes. This phenomenon indicates that the role of traffic conditions in affecting real-world emissions would become weaker when TWC can effectively mitigate emissions. This paper highlights the importance of in-use emission inspection to avoid any “high emitters” that have violated regulation enforcement.

Correlations of Light-duty Gasoline Vehicle Emissions Based on VMAS and CVS Measurement Systems

Gaseous emissions from 25 State 2-5 light-duty gasoline vehicles were tested by Vehicle Mass Analysis System (VMAS) and CVS (Constant Volume Sampling) system, respectively. The correlations of emission factors of tested vehicles measured by these 2 methods were analyzed. The results showed that emission factors of light-duty gasoline vehicle had a decreasing trend with the promotion of emission standard. There were some high-emitting vehicles in the fleet of tested State 2 and State 3 vehicles, but fewer in State 4 or Stated 5 vehicle fleet. The correlations of the emission factors measured by the 2 methods deteriorated with the promotion of emission standard. The relative bias of CO and HC+NOx emission factors measured by the 2 methods reached 197% and 177%, respectively. The correlation coefficient of emission factors of higher-emitting vehicles was 0.75-0.85, while that of lower-emitting vehicles was only 0.46. If tighter emission standard of in-use light-duty gasoline vehicle was adopted, the false positive rate of measurement results by VMAS would rise significantly. In summary, VMAS method is hard to be applied in the emission measurements of light-duty gasoline vehicles with stricter emissions standard. It is necessary to conduct more studies on sophisticated in-use vehicle measurement system.

Impacts and mitigation of excess diesel-related NOx emissions in 11 major vehicle markets.

Vehicle emissions contribute to fine particulate matter (PM2.5) and tropospheric ozone air pollution, affecting human health, crop yields and climate worldwide. On-road diesel vehicles produce approximately 20 per cent of global anthropogenic emissions of nitrogen oxides (NOx), which are key PM2.5 and ozone precursors. Regulated NOx emission limits in leading markets have been progressively tightened, but current diesel vehicles emit far more NOx under real-world operating conditions than during laboratory certification testing. Here we show that across 11 markets, representing approximately 80 per cent of global diesel vehicle sales, nearly one-third of on-road heavy-duty diesel vehicle emissions and over half of on-road light-duty diesel vehicle emissions are in excess of certification limits. These excess emissions (totalling 4.6 million tons) are associated with about 38,000 PM2.5- and ozone-related premature deaths globally in 2015, including about 10 per cent of all ozone-related premature deaths in the 28 European Union member states. Heavy-duty vehicles are the dominant contributor to excess diesel NOx emissions and associated health impacts in almost all regions. Adopting and enforcing next-generation standards (more stringent than Euro 6/VI) could nearly eliminate real-world diesel-related NOx emissions in these markets, avoiding approximately 174,000 global PM2.5- and ozone-related premature deaths in 2040. Most of these benefits can be achieved by implementing Euro VI standards where they have not yet been adopted for heavy-duty vehicles.

The difference between reported and real-world CO 2 emissions: How much improvement can be expected by WLTP introduction?

The monitoring and reporting of CO2 emissions of light duty vehicles in Europe and other major markets is based on the New European Driving Cycle and the accompanying test protocol. This procedure has been proven non-representative of real world vehicle operation, fuel consumption and CO2 emissions leading to a gap between officially reported emissions and the ones experienced during real world operation. This gap is reported to be increasing with time. To address this issue and improve the certification procedure for pollutant emissions of vehicles over real driving, the new Worldwide Harmonized Light duty vehicle Test Protocol was designed. This new test procedure is expected to provide more realistic emission and fuel consumption results. In this paper a first estimate of the certification-reality gap under the present (2015) conditions is attempted and the impact of the new test procedure is investigated. Tests were performed on three real vehicles over the two cycles which allowed the development of representative simulation models. A detailed simulation matrix was subsequently formulated, taking into account the two tests and expected conditions occurring during real world driving. Results show that for 2013-14 model year European passenger cars the difference in certified and actually emitted CO2 emissions for an average European passenger car reaches up to 40 g CO2/km (~32% higher than certification). WLTP introduction is expected to improve the picture, however a shortfall of about 10-15% between official and real world may remain.

Heavy-Duty Diesel Truck Emissions Modeling

Heavy-duty vehicles are the second-largest source of greenhouse gas emissions and energy use within the transportation sector even though they represent only a small portion of on-road vehicles. Heavy-duty diesel vehicles (HDDVs) emit about half of all on-road emissions of nitrogen oxide (NOx). However, because of the limited amount of HDDV emissions data, research has focused on light-duty vehicle emissions. The majority of these microscopic models suffer from two major limitations: the models result in a bang-bang control system and calibration of the model parameters is not possible with publicly available data. This paper proposes to extend the Virginia Tech Comprehensive Power-Based Fuel Consumption Model (VT-CPFM) to overcome the two shortcomings in state-of-the-practice HDDV emissions models of carbon monoxide (CO), hydrocarbons (HCs), and NOx. Heavy-duty diesel truck (HDDT) data from the University of California, Riverside, were used for the calibration and validation processes. The study’s results were satisfying, especially for NOx, which was the main concern in HDDV emissions. Model validity and performance were evaluated by comparing the correlation of measured field data and estimated emissions between the VT-CPFM model and the comprehensive modal emissions model (CMEM). The results demonstrate the efficacy of the VT-CPFM model in replicating empirical observations producing better accuracy compared with other state-of-the-practice models (e.g., CMEM). Moreover, unlike the CMEM model, which requires extensive data collection for calibration purposes, the VT-CPFM model needs only GPS and publicly accessible data for calibration.

A K-Nearest Neighbor Model of Light-Duty Vehicle Emission Factors Considering Pavement Roughness

Emission factors are very important measures for developing an emission inventory, making decisions, designing control strategies, mitigating climate change, and even improving public health, in terms of respiratory system diseases. The emission factors could be either measured from field tests or estimated by an emission model. Existing models seldom consider the impacts of some special factors such as pavement roughness. As the impacts of the pavement roughness on emissions are very complicated, a linear model or physical model may not depict the mappings from affecting factors to resulted emission factors. In this paper, two non-linear models, including K-Nearest Neighbor (KNN) and Neural Network (NN) were built to estimate vehicle emission factors using roughness involved input data. A best fitted model was identified to illustrate the emission pattern along a wide range of pavement roughness. Multiple field tests were conducted in five regions of the State of Texas, United States, with a total of 1,609 km test length. One dedicated test vehicle was employed throughout the test. Pavement roughness was tested using a smartphone based application. All tested data were separated into four groups, each representing a different range of roughness, while the modeling was conducted within each group. The predictive performance of each model was evaluated by (1) correlation coefficient; (2) relative errors; and (3) two tailed unequal variance t-test. Results suggest that, K-NN can be better than NN to model the emission factors for the Texas highway system, and driving on a smoother and rougher pavement result in higher vehicle emissions.

Euro6 소형 경유자동차의 실제 도로 주행 NOx 배출량 평가

To protect air pollution of urban area from motor vehicles, emission limits for diesel vehicles have been dramatically lowered in short period. But recent studies have shown that on-road NOx emissions of light-duty diesel vehicles are considerably higher than the values measured with laboratory test procedures used for emission certification. To tackle with this issue, Ministry of Environment have a plan to introduce EU RDE-LDV (Real-driving Emission-Light-duty Vehicle) regulation. In this study, 4 Euro 6 diesel vehicles have been tested with the new test procedures published by EU to estimate on-road NOx emissions using PEMS (Portable Emission Measurement System). The results have shown that the requirements of EU RDE-LDV could be met in driving condition of metropolitan area for constitution of test routes and validity of test results. In analysing with Moving Averaging Window method the completeness and normality of test data were validated with the requirement. On-road NOx emissions were quite deviated as test vehicles and higher than the new limit of on-road NOx emission enforced from Sept. 2017, which means that RDE-LDV can effectively reduce NOx emission of diesel vehicles in real driving conditions of Korea.

Performance and emissions of light-duty diesel vehicle fuelled with non-surfactant low grade diesel emulsion compared with a high grade diesel in Malaysia

The use of water-in-diesel (W/D) emulsion as a diesel substitute has imposed significant interest due to its benefits to engine performance and exhaust emissions. However, the development on emulsification technology especially without using surfactant is still not widely known. Therefore, in this study, a study into the application of non-surfactant W/D emulsion has been done with the objective to analyze the potential of non-surfactant W/D emulsion made from low grade diesel as a substitute for higher grade diesel. This study was conducted using light-duty diesel vehicle, a 1ton truck tested in a chassis dynamometer. A variety of test fuels was used, comprises of Diesel Euro 5 (DE5), Diesel Euro 2 (DE2) and emulsion made from Diesel Euro 2 (EDE2). EDE2 was produced real time just before it is injected into the diesel engine, with water percentage of 6.5% and no additional surfactant. The testing was executed on a chassis dynamometer in accordance to the West Virginia (WVU) 5 Peak-Cycle standard. Among the data collected are fuel consumption, exhaust temperature, gas emissions (NOx, CO and CO2) and smoke number. The results show that the EDE2 improved the engine fuel consumption by 7.39% compared to DE5. As for exhaust emissions, EDE2 produced slightly higher NOx and CO compared to DE5. However, CO2 and smoke of EDE2 were found to be lower. For that reason, with some adjustments, non-surfactant W/D emulsion fuel made from low grade diesel has a potential to be applied in road transport with some adjustment in order to replace the high grade diesel.

Highway Vehicle Emissions Avoided by Diesel Passenger Rail Service Based on Real-World Data

Avoided emissions attributable to the reduction in personal automobile trips for passenger rail riders are quantified based on real-world measurements. The North Carolina Department of Transportation (NCDOT) sponsors the Piedmont passenger rail service between Raleigh and Charlotte, NC. Per passenger-kilometer locomotive emissions were quantified based on portable emissions measurement system measured exhaust concentrations and duty cycles, or the fraction of trip time spent in each throttle notch setting of the prime mover engine, from 68 one-way trips of six Tier 0+ and Tier 1+ locomotives, and actual ridership data. Motor Vehicle Emissions Simulator (MOVES) software was used to estimate light-duty gasoline vehicle (LDGV) emission factors. Moving a passenger from an LDGV to a Piedmont train would lead to a net reduction in carbon dioxide (CO2) and carbon monoxide (CO) emissions by 44–94 %, respectively, between Raleigh and Charlotte, based on the assumption that the driver is the only LDGV passenger. However, locomotive nitrogen oxides (NO x ), hydrocarbons (HC), and particulate matter (PM) emission factors were 4–11 times higher than for the LDGV, respectively. Delays for either the train or highway vehicles did not substantially alter the key findings. If a Tier 4 locomotive was used, NO x , PM, and HC emission rates would be 90–99 % lower than current NCDOT locomotives. The use of real-world data representative of actual train operations provides an accurate basis for comparing rail and personal vehicle energy use and emissions and for identifying key factors affecting variability in the comparison.

Using a new inversion matrix for a fast-sizing spectrometer and a photo-acoustic instrument to determine suspended particulate mass over a transient cycle for light-duty vehicles

Integrated particle size distribution (IPSD) is a promising alternative method for estimating particulate matter (PM) emissions at low levels. However, a recent light-duty vehicle (LDV) emissions study showed that particle mass estimated using IPSD (MIPSD) with the TSI Engine Exhaust Particle Sizer (EEPS) Default Matrix was 56–75% lower than mass derived using the reference gravimetric method (MGrav) over the Federal Test Procedure (FTP). In this study, MIPSD calculated with a new inversion matrix, the Soot Matrix, is compared with MGrav and also photoacoustic soot mass (MSoot), to evaluate potential improvement of the IPSD method for estimating PM mass emissions from LDVs. In addition, an aerodynamic particle sizer (APS) was used to estimate mass emission rates attributed to larger particles (0.54–2.5 µm in aerodynamic diameter) that are not measured by the EEPS. Based on testing of 10 light-duty vehicles over the FTP cycle, the Soot Matrix significantly improved agreement between MIPSD and MGrav by increasing slopes of MIPSD/MGrav from 0.45–0.57 to 0.76–1.01 for gasoline direct injected (GDI) vehicles; however, for port-fuel injection (PFI) gasoline vehicles, a significant discrepancy still existed between MIPSD and MGrav, with MIPSD accounting for 34 ± 37% of MGrav. For all vehicles, strong correlations between MIPSD and MSoot were obtained, indicating the IPSD method is capable of capturing mass of soot particles. The discrepancy between the MIPSD and MGrav for PFI vehicles, which have relatively low PM emissions (0.22 to 1.83 mg/mile), could be partially due to limited size range of the EEPS by not capturing larger particles (0.54–2.5 µm) that accounts for ∼0.08 mg/mile of PM emission, uncertainties of particle effective density, and/or gas-phase adsorption onto filters that is not detected by in situ aerosol instrumentation.Copyright © 2016 American Association for Aerosol Research

Emissions, performance, and design of UK passenger vehicles

ABSTRACTConsumer, legal, and technological factors influence the design, performance, and emissions of light-duty vehicles (LDVs). This work examines how design choices made by manufacturers for the UK market result in emissions and performance of vehicles throughout the past decade (2001–2011). LDV fuel consumption, CO2 emissions, and performance are compared across different combinations of air and fuel delivery system using vehicle performance metrics of power density and time to accelerate from rest to 100 km/h (62 mph, tz-62). Increased adoption of direct injection and turbocharging technologies helped reduce spark ignition (SI, gasoline vehicles) and compression ignition (CI, diesel vehicles) fuel consumption by 22% and 19%, respectively, over the decade. These improvements were largely achieved by increasing compression ratios in SI vehicles (3.6%), turbocharging CI vehicles, and engine downsizing by 5.7–6.5% across all technologies. Simultaneously, vehicle performance improved, through increased engine power density resulting in greater acceleration. Across the decade, tz-62 fell 9.4% and engine power density increased 17% for SI vehicles. For CI vehicles, tz-62 fell 18% while engine power density rose 28%. Greater fuel consumption reductions could have been achieved if vehicle acceleration was maintained at 2001 levels, applying drive train improvements to improved fuel economy and reduced CO2 emissions. Fuel consumption and CO2 emissions declined at faster rates once the European emissions standards were introduced with SI CO2 emissions improving by 3.4 g/km/year for 2001–2007 to 7.8 g/km/year thereafter. Similarly, CI LDVs declined by 2.0 g/km/year for 2001–2007 and 6.1 g/km/year after.

Reducing emissions at land border crossings through queue reduction and expedited security processing

Vehicle border crossings between Mexico and the United States generate significant amounts of air pollution, which can pose health threats to personnel at the ports of entry (POEs) as well as drivers, pedestrians, and local inhabitants. Although these health risks could be substantial, there is little previous work quantifying detailed emission profiles at POEs. Using the Mariposa POE in Nogales, Arizona as a case study, light-duty and heavy-duty vehicle emissions were analyzed with the objective of identifying effective emission reduction strategies such as inspection streamlining, physical infrastructure improvements, and fuel switching. Historical traffic information as well as field data were used to establish a simulation model of vehicle movement in VISSIM. Four simulation scenarios with varied congestion levels were considered to represent real-world seasonal changes in traffic volume. Four additional simulations captured varying levels of expedited processing procedures. The VISSIM output was analyzed using the EPA’s MOVES emission simulation software for conventional air pollutants. For the highest congestion scenario, which includes a 200% increase in vehicle volume, total emissions increase by around 460% for PM2.5 and NOx, and 540% for CO, SO2, GHGs, and NMHC over uncongested conditions for a two-hour period. Expedited processing and queue reduction can reduce emissions in this highest congestion scenario by as much as 16% for PM2.5, 18% for NOx, 20% for NMHC, 7% for SO2 and 15% for GHGs and CO. Other potential mitigation strategies examined include fleet upgrades, fuel switching, and fuel upgrades. Adoption of some or all of these changes would not only reduce emissions at the Mariposa POE, but would have air-quality benefits for nearby populations in both the US and Mexico. Fleet-level changes could have far-reaching improvements in air quality on both sides of the border.

High-Mileage Light-Duty Fleet Vehicle Emissions: Their Potentially Overlooked Importance.

State and local agencies in the United States use activity-based computer models to estimate mobile source emissions for inventories. These models generally assume that vehicle activity levels are uniform across all of the vehicle emission level classifications using the same age-adjusted travel fractions. Recent fuel-specific emission measurements from the SeaTac Airport, Los Angeles, and multi-year measurements in the Chicago area suggest that some high-mileage fleets are responsible for a disproportionate share of the fleet's emissions. Hybrid taxis at the airport show large increases in carbon monoxide, hydrocarbon, and oxide of nitrogen emissions in their fourth year when compared to similar vehicles from the general population. Ammonia emissions from the airport shuttle vans indicate that catalyst reduction capability begins to wane after 5-6 years, 3 times faster than is observed in the general population, indicating accelerated aging. In Chicago, the observed, on-road taxi fleet also had significantly higher emissions and an emissions share that was more than double their fleet representation. When compounded by their expected higher than average mileage accumulation, we estimate that these small fleets (<1% of total) may be overlooked as a significant emission source (>2-5% of fleet emissions).

The problem of cold starts: A closer look at mobile source emissions levels

While the phenomenon of excess vehicle emissions from cold-start conditions is well known, the magnitude and duration of this phenomenon is often unclear due to the complex chemical processes involved and uncertainty in the literature on this subject. This paper synthesizes key findings regarding the influence of ambient and engine temperatures on light-duty vehicle (LDV) emissions. Existing literature, as well as analytical tools like the U.S. Environmental Protection Agency’s Motor Vehicle Emission Simulator (MOVES), indicate that while total vehicle emissions have dropped significantly in recent years, those associated with cold starts can still constitute up to 80% for some pollutant species. Starting emissions are consistently found to make up a high proportion of total transportation-related methane (CH4), nitrous oxide (N2O), and volatile organic compounds (VOCs). After 3–4min of vehicle operation, both the engine coolant and the catalytic converter have generally warmed, and emissions are significantly lower. This effect lasts roughly 45min after the engine is shut off, though the cooling rate depends greatly on the emission species and ambient temperature. Electrically (pre-)heated catalysts, using the bigger batteries available on hybrid drivetrains and plug-in vehicles, may be the most cost-effective technology to bring down a sizable share of mobile source emissions. Trip chaining (to keep engines warm) and shifting to non-motorized modes for shorter trips, where the cold start can dominate emissions, are also valuable tactics.

Comparative Evaluation of the Effect of Various Technologies on Light-duty Vehicle CO2 Emissions over NEDC and WLTP

The paper presents the results of the effect of various fuel economy technologies on the certified CO2 emissions of light duty vehicles. The vehicles operate under two different driving cycles, namely the New European Driving Cycle (NEDC) and the Worldwide harmonized Light duty Test Procedure (WLTP), which is considered closer to real world driving and is going to be the new type approval test in the near future. The study focuses on the comparative evaluation of the effect of each technology on CO2 emissions under these two driving cycles. To this aim, simulation models for a number of passenger cars were developed and validated against test data, generated via a specifically developed test protocol. In order to cover a large share of the market, the European fleet was divided into a number of segments based on specific vehicle characteristics and technologies, and representative vehicles for each segment were chosen. In order to minimize flexibilities and sources of uncertainty, the models were developed according to a standardized modelling procedure, based on the development of a reference “template model”. AVL's Cruise was used as simulation platform. The various components and modules for each vehicle model, as well as the respective input parameters, were defined with the support of the respective OEMs. After gaining confidence in the simulation models for all the vehicles considered in the present work, additional technologies, such as start-stop, brake energy recuperation and different drivetrain configurations, were implemented in each model. Specific strategies have been defined for the implementation of individual technologies and, where needed, additional algorithms were developed in Cruise. The results show that the effect of each technology on CO2 emissions is different between NEDC and WLTP, owing to the different characteristics of each cycle. For example, the effect of start-stop on CO2 emissions is larger in NEDC, due to longer idling periods compared to WLTP. In this context, the results of this study can provide useful indications for the most effective fuel economy technologies under the new type approval procedure.

Operations and Emissions Characteristics of Light-Duty Vehicles on Ramps

Ramps serve as the connections between restricted access highways and other road facilities, and considering the intensity of acceleration and deceleration occurring on ramps, the operation on ramps may contribute a significant amount of criteria-pollutant and greenhouse gas emissions from highway operation. In this study, second-by-second speed and position data were collected from 10 vehicles in the Detroit, Michigan, metropolitan area during their daily commute trips in 2012 using a portable activity measurement system. Ramp-associated operations were extracted from these measurements using ArcGIS, and emission rates were assigned based on model runs of the MOtor Vehicle Emission Simulator, or MOVES. In general, emissions of light-duty vehicles estimated for ramp operation are about two to three times higher than those for highway operation (excluding ramps) and local cycles with average speed levels higher than 30 mph. Emissions for interchange ramps are estimated to be similar to highway emissions. Accelerations occurring immediately after vehicles enter the highway from on-ramps contribute a large portion of emissions from ramp operations, since high-power operations are involved. This point applies especially to loop on-ramps, where the emission rate immediately after entering the highways tends to be higher than driving within the physical ramp itself. This research will be useful for understanding basic ramp operation characteristics and their emissions effects, and it will be important for development of ramp classification systems and generic ramp driving cycles, for emissions modeling and ramp hot-spot analysis.

Estimation of light duty vehicle emissions in Islamabad and climate co-benefits of improved emission standards implementation

Abstract Light Duty Vehicles (LDVs) hold a major share in Islamabad's vehicle fleet and their contribution towards air pollution has not been analyzed previously. Emissions for the base year (2014) and two optimistic ‘what-if’ scenarios were estimated by using the International Vehicle Emissions (IVE) model. Considering the recent implementation of Euro II as emission standard in Pakistan, scenario 1 assumed entire LDV fleet meeting at least Euro II standards while scenario 2 assumed all LDVs meeting Euro IV standards except motorcycles which would be meeting Euro III emission standards. Higher average age for all vehicles and lower share of Euro compliant vehicles was found in the base case. Low engine stress mode (lower speeds with frequent decelerations) was observed for all vehicles especially on arterials and residential roads. Highest overall emissions (59%) were observed on arterials, followed by residential roads (24%) and highways (17%) with higher emissions observed during morning (8–10 am) and evening (4–6 pm) rush hours. Composite emission factors were also calculated. Results reveal that 1094, 147, 11.1, 0.2 and 0.4 kt of CO 2 , CO, NOx, SO 2 and PM 10 respectively were emitted in 2014 by LDVs. Compared with the base year, scenario 1 showed a reduction of 9%, 69%, 73%, 13% and 31%, while scenario 2 exhibited a reduction of 5%, 92%, 90%, 92% and 81% for CO 2 , CO, NOx, SO 2 and PM 10 respectively. As compared to the base year, a 20 year CO 2 -equivalent Global Warming Potential (GWP) reduced by 55% and 64% under scenario 1 and 2 respectively, while a 100 year GWP reduced by 40% and 44% under scenario 1 and 2 respectively. Our results demonstrated significant co-benefits that could be achieved in emission reduction and air quality improvement in the city by vehicle technology implementation.

Impact of fuel, injection type and after-treatment system on particulate emissions of light-duty vehicles using different fuels on FTP-75 and HWFET test cycles

The characteristics of particulate emission, in relation to factors such as fuel, injection type, after-treatment system and test cycle, were investigated. Five light-duty vehicles with different fuel, injection types and after-treatment systems - Compressed Natural Gas (CNG), Gasoline (Port Injection/Direct injection), and Diesel (with/without Diesel Particulate Filter (DPF)) - were tested on Federal Test Procedure (FTP) -75 and Highway Fuel Economy Test (HWFET) cycles. Particulate emissions were measured using a TSI 3090 Engine Exhaust Particle Sizer (EEPS) and Horiba Solid Particulate Counting system (SPCS). For the FTP-75 cycle, the DPF-equipped diesel vehicle showed the lowest particulate emission for the EEPS system, while CNG showed the lowest emission for the SPCS system due to the difference between the two measurement systems. However, the DPF-equipped diesel showed the least PN emission for both EEPS and SPCS method on the HWFET test cycle. Except for the DPF-equipped diesel, fuels with lighter molecular weight generated fewer particulates. Aside from fuel-type, the status of the engine was the most important factor determining particulate emission. When the engine was cold, a large number of particulates is formed regardless of engine-operating conditions. In contrast, warm engines form particulates only if the load on the engine is high enough, and the absolute magnitude is also lower than during the cold-start condition.

Variability in Light-Duty Gasoline Vehicle Emission Factors from Trip-Based Real-World Measurements.

Using data obtained with portable emissions measurements systems (PEMS) on multiple routes for 100 gasoline vehicles, including passenger cars (PCs), passenger trucks (PTs), and hybrid electric vehicles (HEVs), variability in tailpipe emission rates was evaluated. Tier 2 emission standards are shown to be effective in lowering NOx, CO, and HC emission rates. Although PTs are larger, heavier vehicles that consume more fuel and produce more CO2 emissions, they do not necessarily produce more emissions of regulated pollutants compared to PCs. HEVs have very low emission rates compared to tier 2 vehicles under real-world driving. Emission factors vary with cycle average speed and road type, reflecting the combined impact of traffic control and traffic congestion. Compared to the slowest average speed and most congested cycles, optimal emission rates could be 50% lower for CO2, as much as 70% lower for NOx, 40% lower for CO, and 50% lower for HC. There is very high correlation among vehicles when comparing driving cycles. This has implications for how many cycles are needed to conduct comparisons between vehicles, such as when comparing fuels or technologies. Concordance between empirical and predicted emission rates using the U.S. Environmental Protection Agency's MOVES model was also assessed.

Emissions of Light-Duty Vehicles with Respect to Cruising Speed under Real-World Driving Conditions

AbstractMobile-source emission inventories in countries such as Mexico still require empirical data to complement modeling tools because these tools are based on few local observations. In this study, emission factors (EFs) were determined for 10 light-duty gasoline-powered vehicles as a function of cruising speed under real-world driving conditions typical of the Monterrey metropolitan area, the third largest urban center in Mexico. Greater variability in the EF was found when the vehicles were operated at lower speeds, specifically at 10 km/h; however, above 40 km/h, the changes were marginal. Engine size was the factor that most influenced the emissions of CO2, which were significantly greater in vehicles with an engine size above 2 L. A reduction trend in the CO-to-NOx ratio of newer model vehicles was observed. Upon comparison of the experimental results with the results obtained from the MOBILE6.2-Mexico and the MOVES 2010a models, it was determined that the latter model better described the value...