Real-world gaseous emission characteristics of Euro 6b light-duty gasoline- and diesel-fueled vehicles

To accurately investigate vehicle emissions that have become major contributors to global air pollutants and greenhouse gases, test conditions have been transferred from laboratory type approval test cycles to real-world driving conditions. In this study, the real-world driving emissions of carbon monoxide (CO), total hydrocarbons (THC), nitrogen oxides (NO_x), and carbon dioxide (CO₂) from one gasoline and two diesel Euro 6b light-duty passenger vehicles were investigated by a portable emission measurement system (PEMS) in Lyon, France. NO_x and CO₂ emission controls remain critical to addressing the real-world driving emissions of Euro 6b vehicles. Notably, the tested gasoline vehicle emitted higher CO₂ emissions than diesel vehicles on all types of roads, especially on the urban road with an excess of 29.3–48.3%. The highest emission factors of gaseous pollutants generally occurred on the motorway for the gasoline vehicle, while on the urban road for diesel vehicles. In particular, for high-speed driving conditions, the gasoline vehicle gaseous emissions, especially NO_x emissions, were more affected by acceleration than diesel vehicle emissions. In addition, the CO emissions, especially THC emissions, for the gasoline vehicle, were more influenced by warm-start, especially cold-start, than those for diesel vehicles.     

Real-world gaseous and particle emissions of a Bi-fuel gasoline/CNG Euro 6 passenger car

The objective of the present study is the assessment of the environmental impact of a bivalent (bi-fuel) vehicle, running either on gasoline or compressed natural gas (CNG). To that aim, a Euro 6 passenger car was tested under various real-world driving conditions. In order to cover the full range of conventional powertrains currently in the market, the tests were also repeated on a Euro 6 diesel passenger car. Both cars were driven in two routes, the first complying with the regulation limits and the second going beyond them. Carbon monoxide (CO), nitrogen oxides (NO_x) and particle number (PN) emissions were recorded using a Portable Emissions Measurement System (PEMS). Apart from the aggregated emission levels, in g/km, the exact emission location along the route was also assessed. Natural gas proved beneficial for CO and PN emissions, the level of which always remained below the respective legislation limits. On the other hand, under the dynamic driving conditions with gasoline, the relevant limits were exceeded. Cold start, occurring at the beginning of the urban part, and motorway driving were identified as major contributors to total emissions, especially in gasoline mode. However, the application of natural gas was associated with a penalty in NO_x emissions, which were significantly increased as compared to gasoline. Local peaks within the urban part were identified in CNG mode. In any case, the diesel vehicle was by far the highest NO_x emitter.     

The economy of alternative fuels when including the cost of air pollution

In this study, the costs involved in the use of petrol, diesel, natural gas, biogas, and methanol (produced from natural gas and biomass) in cars and heavy trucks are compared. The cost includes fuel cost, extra capital cost for vehicles using alternative fuels, and the environmental cost of VOC, NO_x, particulate and CO₂ emission based on actual 1996 and estimated 2015 emission factors. The costs have been calculated separately for rural, urban and city-centre traffic. A complete macroeconomic assessment of the effect of introducing alternative fuels is not, however, included in the study. The study shows that no alternative fuel can compete with petrol and diesel in rural traffic when the economic valuation of CO₂ emission is taken as current Swedish CO₂ taxes ($200/tonne C). In cities with a natural gas network, natural gas is the fuel with the lowest cost for both cars and heavy trucks, based on 1996 emission factors. Methanol from natural gas and biogas from waste products can also compete with diesel in urban traffic. With predicted improvements in technology and subsequent emission reductions, no alternative fuel can compete with petrol in any of the traffic situations studied by 2015, and only in city-centre traffic will alternative fuels be less costly than diesel in heavy vehicles. Of the biomass-based fuels studied, low-cost biogas from waste products is the most competitive one and is, already at current CO₂ taxes, the fuel with lowest cost for heavy trucks in urban traffic in areas where natural gas networks do not exist. To enable the more widespread use of biomass-based fuels, i.e. using feedstocks such as energy crops or logging residues that are available in larger amounts, the economic valuation of CO₂ emission has to be 2–2.5 times higher than current Swedish CO₂ tax level.     

Exhaust emissions generated under actual operating conditions from a hybrid vehicle and an electric one fitted with a range extender

The paper describes exhaust emission tests performed on a PHEV (Plug-in Hybrid Electric Vehicle) and a BEV (Battery Electric Vehicle), in which the combustion engine was used as a range extender. The measurements of the exhaust emissions were performed for CO₂/fuel consumption, CO, THC and NO_x. The RDE measurements were performed including the engine operating parameters and emissions analysis. This analysis shows that the engines of BEVs and PHEVs operate in a different parameter range when under actual operating conditions, which directly translates into the exhaust emission values. This is particularly the case for the emission of NO_x. The investigations were carried out for two routes differentiated by the length and share of the urban and extra-urban cycles. For both routes, the emission of THC and CO were lower for the PHEV engine – HC by 69% (22 mg/km, route 1) and 6% (15 mg/km, route 2), CO by 69% (0.12 mg/km, route 1) and 80% (0.1 mg/km, route 2). For route 1, characterized by a greater share of the urban cycle, the emission of NO_x was lower by 70% (2 mg/km) for the BEV engine, and (route 2) lower by 60% (8 mg/km) for the PHEV engine. Additionally, the curves of the exhaust emissions in time for individual exhaust components have been presented that indicate that in the motorway cycle the emission of THC and CO from the BEV vehicle increases significantly up to ten times compared to urban cycle.     

Analysis of fuel consumption and pollutant emissions of regulated and alternative driving cycles based on real-world measurements

Discrepancies between real-world use of vehicles and certification cycles are a known issue. This paper presents an analysis of vehicle fuel consumption and pollutant emissions of the European certification cycle (NEDC) and the proposed worldwide harmonized light vehicles test procedure (WLTP) Class 3 cycle using data collected on-road. Sixteen light duty vehicles equipped with different propulsion technologies (spark-ignition engine, compression-ignition engine, parallel hybrid and full hybrid) were monitored using a portable emission measurement system under real-world driving conditions. The on-road data obtained, combined with the Vehicle Specific Power (VSP) methodology, was used to recreate the dynamic conditions of the NEDC and WLTP Class 3 cycle. Individual vehicle certification values of fuel consumption, CO₂, HC and NO_x emissions were compared with test cycle estimates based on road measurements. The fuel consumption calculated from on-road data is, on average, 23.9% and 16.3% higher than certification values for the recreated NEDC and WLTP Class 3 cycle, respectively. Estimated HC emissions are lower in gasoline and hybrid vehicles than certification values. Diesel vehicles present higher estimated NO_x emissions compared to current certification values (322% and 326% higher for NO_x and 244% and 247% higher for HC + NO_x for NEDC and WLTP Class 3 cycle, respectively).     

Well-to-wake energy and greenhouse gas analysis of SOX abatement options for the marine industry

This paper investigates the well-to-wake energy consumption and greenhouse gas emissions of several key SO_X abatement options in marine transportation, ranging from the manufacture of low sulfur fuels to equipping the vessel with suitable scrubber solutions. The findings suggest that a scrubber system, used with current heavy fuel oils, has the potential to reduce SO_X emissions with lower well-to-wake energy consumption and greenhouse gas emissions than switching to production of low sulfur fuels at the refinery. A sensitivity analysis covering a series of system parameters shows that variations in the well-to-tank greenhouse gas emissions intensity and the energy efficiency of the main engine have the highest impacts in terms of well-to-wake emissions.     

Influence of driving patterns on vehicle emissions: A case study for Latin American cities

On-board real-time emission experiments were conducted on 78 light-duty vehicles in Bogota. Direct emissions of carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NO_x) and hydrocarbons (HC) were measured. The relationship between such emissions and vehicle specific power (VSP) was established. The experimental matrix included both gasoline-powered and retrofit dual fuel (gasoline–natural gas) vehicles. The results confirm that VSP is an appropriate metric to obtain correlations between driving patterns and air pollutant emissions. Ninety-five percent of the time vehicles in Bogota operate in a VSP between −15.2 and 17.7 kW ton⁻¹, and 50% of the time they operate between −2.9 and 1.2 kW ton⁻¹, representing low engine-load and near-idling conditions, respectively. When engines are subjected to higher loads, pollutant emissions increase significantly. This demonstrates the relevance of reviewing smog check programs and command-and-control measures in Latin America, which are widely based on static (i.e., idling) emissions testing. The effect of different driving patterns on the city’s emissions inventory was determined using VSP and numerical simulations. For example, improving vehicle flow and reducing sudden and frequent accelerations could curb annual emissions in Bogota by up to 12% for CO₂, 13% for CO and HC, and 24% for NO_x. This also represents possible fuel consumption savings of between 35 and 85 million gallons per year and total potential economic benefits of up to 1400 million dollars per year.     

Performance and emission characteristics of a spark ignition engine fuelled with butanol isomer-gasoline blends

The heavy reliance on petroleum-derived fuels such as gasoline in the transportation sector is one of the major causes of environmental pollution. For this reason, there is a critical need to develop cleaner alternative fuels. Butanol is an alcohol with four different isomers that can be blended with gasoline to produce cleaner alternative fuels because of their favourable physicochemical properties compared to ethanol. This study examined the effect of butanol isomer-gasoline blends on the performance and emission characteristics of a spark ignition engine. The butanol isomers; n-butanol, sec-butanol, tert-butanol and isobutanol are mixed with pure gasoline at a volume fraction of 20 vol%, and the physicochemical properties of these blends are measured. Tests are conducted on a SI engine at full throttle condition within an engine speed range of 1000–5000 rpm. The results show that there is a significant increase in the engine torque, brake power, brake specific fuel consumption and CO₂ emissions with respect to those for pure gasoline. The butanol isomers-gasoline blends give slightly higher brake thermal efficiency and exhaust gas temperature than pure gasoline at higher engine speeds. The iBu20 blend (20 vol% of isobutanol in gasoline) gives the highest engine torque, brake power and brake thermal efficiency among all of the blends tested in this study. The isobutanol and n-butanol blend results in the lowest CO and HC emissions, respectively. In addition, all of the butanol isomer-gasoline blends yield lower NO emissions except for the isobutanol-gasoline blend.     

Assessing the importance of transportation activity data for urban emission inventories

The aim of this research is the implementation of a GPS-based modelling approach for improving the characterization of vehicle speed spatial variation within urban areas, and a comparison of the resulting emissions with a widely used approach to emission inventory compiling. The ultimate goal of this study is to evaluate and understand the importance of activity data for improving the road transport emission inventory in urban areas. For this purpose, three numerical tools, namely, (i) the microsimulation traffic model (VISSIM); (ii) the mesoscopic emissions model (TREM); and (iii) the air quality model (URBAIR), were linked and applied to a medium-sized European city (Aveiro, Portugal). As an alternative, traffic emissions based on a widely used approach are calculated by assuming a vehicle speed value according to driving mode. The detailed GPS-based modelling approach results in lower total road traffic emissions for the urban area (7.9, 5.4, 4.6 and 3.2% of the total PM10, NO_x, CO and VOC daily emissions, respectively). Moreover, an important variation of emissions was observed for all pollutants when analysing the magnitude of the 5th and 95th percentile emission values for the entire urban area, ranging from −15 to 49% for CO, −14 to 31% for VOC, −19 to 46% for NO_x and −22 to 52% for PM10. The proposed GPS-based approach reveals the benefits of addressing the spatial and temporal variability of the vehicle speed within urban areas in comparison with vehicle speed data aggregated by a driving mode, demonstrating its usefulness in quantifying and reducing the uncertainty of road transport inventories.     

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 PM_2.5 and NO_x, 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 PM_2.5, 18% for NO_x, 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.     

Well-to-wheel assessment of natural gas vehicles and their fuel supply infrastructures – Perspectives on gas in transport in Denmark

In this paper, potential natural gas and renewable natural gas supply pathways and natural gas vehicles (NGVs) have been selected and evaluated with regards to well-to-wheel energy expended, greenhouse gas (GHG) emissions, and regulated (air pollutant) emissions. The vehicles included in the evaluation are passenger cars, light-duty vehicles (LDVs), and heavy-duty vehicles (HDVs) for road-transport applications, and a short-range passenger vessel for maritime transport applications. The results show that, compared to conventional fuels, in both transport applications and for all vehicle classes, the use of compressed and liquefied natural gas has a 15–27% GHG emissions reduction effect per km travel. The effect becomes large, 81–211%, when compressed and liquefied renewable natural gas are used instead. The results are sensitive to the type and source of feedstock used, the type of vehicle engine, assumed methane leakage and methane slip, and the allocated energy and environmental digestate credits, in each pathway. In maritime applications, the use of liquefied natural gas and renewable natural gas instead of low sulfur marine fuels results in a 60–100% SOx and 90–96% PM emissions reduction. A 1% methane slip from a dedicated LNG passenger vessel results, on average, in 8.5% increase in net GHG emissions.     

Investigation of tailpipe and evaporative emissions from China IV and Tier 2 passenger vehicles with different gasolines

The limited understanding of vehicular emissions in China, especially evaporative emissions, is one obstacle to establishing tighter standards. To evaluate tailpipe and evaporative emissions, two typical China IV vehicles and one Tier 2 vehicle with an onboard refuelling vapour recovery (ORVR) system were selected and tested. One of the China IV vehicles was fuelled with gasoline, E10 and M15, respectively, to investigate the effect of fuel properties on vehicular emissions. For each vehicle, cold-start tailpipe emission tests were conducted first, followed by an evaporation test. Based on the emission factors and real-world vehicle activity data, the annual tailpipe and evaporative hydrocarbon (HC) emissions of each vehicle were calculated and compared. The results show that E10 and M15 significantly reduced the tailpipe CO and particle number (PN) emissions but seriously aggravated the NOx emissions, especially for M15. The hot soak losses (HSLs) and diurnal breathing losses (DBLs) were slightly impacted by the fuel properties. The annual evaporative emissions with E10 and M15 were higher than that with gasoline. The ORVR system effectively controlled the evaporative emissions, especially for DBLs. Evaporative emissions from the China IV vehicles were 1.1–1.4 times the tailpipe HC emissions. Additionally, the evaporative emission factors of the China IV vehicles were almost 50% lower than the standard (2.0 g/test), whereas their annual evaporative emissions were almost 1.8–2.8 times higher than those from the Tier 2 vehicle. Therefore, controlling evaporative emissions currently remains a great need in China, and the ORVR might be a recommended evaporative control technology.     

The vehicle emissions and performance monitoring system: analysis of tailpipe emissions and vehicle performance

This paper describes tailpipe emission results generated by the Vehicle Performance and Emissions Monitoring system (VPEMS). VPEMS integrates on‐board emissions and vehicle/driver performance measurements with positioning and communications technologies, to transmit a coherent spatio‐temporally referenced dataset to a central base station in near real time. These results focus on relationships between tailpipe emissions of CO, CO₂, NO_x and speed and acceleration. Emissions produced by different driving modes are also presented. Results are generally as one would expect, showing variation between vehicle speed, vehicle acceleration and emissions. Data is based upon a test run in central London on urban streets with speeds not exceeding about 65 km/h. The results presented demonstrate the capabilities of the system. Various issues remain with regard to validation of the data and expansion of the system capability to obtain additional vehicle performance data.     

Analysis of real driving gaseous emissions from light-duty diesel vehicles

Increasingly strict emissions standards are providing a major impetus to vehicle manufactures for developing advanced powertrain and after-treatment systems that can significantly reduce real driving emissions. The knowledge of the gaseous emissions from diesel engines under steady-state operation and under transient operation provides substantial information to analyze real driving emissions of diesel vehicles. While there are noteworthy advances in the assessment of road vehicle emissions from real driving and laboratory measurements, detailed information on real driving gaseous emissions are required in order to predict effectively the real-time gaseous emissions from a diesel vehicle under realistic driving conditions. In this work, experiments were performed to characterize the behavior of NOx, unburned HC, CO, and CO₂ emitted from light-duty diesel vehicles that comply with Euro 6 emissions standards. The driving route fully reflected various real-world driving conditions such as urban, rural, and highway. The real-time emission measurements were conducted with a Portable Emissions Measurement System (PEMS) including a Global Positioning System (GPS). To investigate the gaseous emission characteristics, authors determined the road load coefficients of vehicle specific power (VSP) and regression coefficient between fuel use rate and VSP. Furthermore, this work revealed the correlation between the rates of average fuel use and each gaseous emission.     

On-road emissions from urban buses with SCR + Urea and EGR + DPF systems using diesel and biodiesel

Due to growing concerns about NO_x and particulate matter (PM) emissions from diesel engines, stricter regulations are being introduced requiring advanced emission control technology. In response the diesel industry has begun testing various emission control technologies and applying them. To assess vehicle renewal policies of bus companies, two exhaust after-treatment technologies are compared: the combination of a diesel particulate filter and an exhaust gas re-circulation system and the combination of a selective catalytic reduction and urea. On-board emission measurements were conducted under real-world driving conditions on a specific bus route in the city of Madrid.     

The impact of marine engine operation and maintenance on emissions

This paper examines the role of marine engine maintenance in reducing pollution. It tests four marine diesel engines, one constructed prior to January 1, 2000 and three after 2000. This paper explains how the condition of an engine’s nozzles and faulty injection pressure significantly influence NO_x and CO emissions and describes both bench and onboard ship tests, on engines fitted with new or worn nozzles at different injection pressures. The tests showed that, when the engine constructed prior to 2000 operates under normal in-service conditions, the emissions are within limits, but, with a small fault in injection timing, the NO_x emissions exceed the limits. For the engines constructed after 2000, a fault in the maintenance of the nozzles increases the CO emissions to a high level.     

A statistical model for estimating oxides of nitrogen emissions from light duty motor vehicles

Motor vehicle emission rate models for predicting oxides of nitrogen (NOx) emissions are insensitive to vehicle modes of operation such as cruise, acceleration, deceleration, and idle, because they are based on average trip speed. Research has shown that NOx emissions are sensitive to engine load; hence, load-based variables need to be included in emissions models. Ongoing studies attempting to incorporate these `modal' variables have experienced difficulties with: (1) incomplete and/or non-representative data sets of emissions test data vis-a-vis the modal operating profiles of the tested vehicles; (2) lack of information for predicting on-road operating parameters of vehicles; and (3) non-representative vehicles recruited for emissions tests.The objective of this research was to develop a statistical model for predicting NOx emissions from light-duty gasoline motor vehicles. The primary end use of this model is forecasting, rather than explanation of the factors that affect NOx emissions, which brings to bear different requirements from the statistical model. The three challenges noted above are addressed by: (1) analyzing a data set of more than 13 000 hot-stabilized laboratory treadmill tests on 19 driving cycles (specific speed versus time testing conditions), and 114 variables describing vehicle, engine and test cycle characteristics; (2) making the models compatible with empirical data on how vehicles are being operated in-use; and (3) developing statistical weights to account for the differences in model year distributions between the emissions testing database and the current national on-road fleets.The NOx emissions model is estimated using ordinary least-squares regression techniques, with transformed response variable and regression weights. Tree regression is employed as a tool for mining relationships among variables in the data, with particular focus on identifying useful interactions among discrete variables. Details of the model development process are presented, as well as results for the final model showing the predicted emissions algorithm for the current motor vehicle fleet in Atlanta, GA metropolitan region.     

Energy use and emissions of two stroke-powered tricycles in Metro Manila

CO, CO₂, NO_x and HC emissions of two stroke-powered tricycles in Metro Manila are examined using an instantaneous emissions model. Results show that fuel consumption and HC emissions in middle class residential areas and main roads are similar but lower than levels in low income residential areas. On the average, tricycles in Metro Manila consume 24.41 km/l of fuel and produces 9.5, 9.7, 40.5 and 0.07 g/km of HC, CO, CO₂ and NO_x, respectively. They fail to satisfy HC, CO and NO_x emission limits set by reference standards in the Philippines and other Asian countries. They produce greater HC and CO emissions than gasoline fueled private cars and diesel powered public jeepneys, taxis and buses on a per passenger-km basis but significantly lower NO_x emissions. Tricycles account for 15.4% of the total HC emissions from mobile sources in the metropolis while their contributions to CO, CO₂ and NO_x are minimal.     

Individual exposure to traffic related air pollution across land-use clusters

In this study, we estimated the transportation-related emissions of nitrogen oxides (NO_x) at an individual level for a sample of the Montreal population. Using linear regression, we quantified the associations between NO_x emissions and selected individual attributes. We then investigated the relationship between individual emissions of NO_x and exposure to nitrogen dioxide (NO₂) concentrations derived from a land-use regression model. Factor analysis and clustering of land-uses were used to test the relationships between emissions and exposures in different Montreal areas. We observed that the emissions generated per individual are positively associated with vehicle ownership, gender, and employment status. We also noted that individuals who live in the suburbs or in peripheral areas generate higher emissions of NO_x but are exposed to lower NO₂ concentrations at home and throughout their daily activities. Finally, we observed that for most individuals, NO₂ exposures based on daily activity locations were often slightly more elevated than NO₂ concentrations at the home location. We estimated that between 20% and 45% of individuals experience a daily exposure that is largely different from the concentration at their home location. Our findings are relevant to the evaluation of equity in the generation of transport emissions and exposure to traffic-related air pollution. We also shed light on the effect of accounting for daily activities when estimating air pollution exposure.     

System for assessing Aviation’s Global Emissions (SAGE), Part 2: Uncertainty assessment

This paper focuses on assessing and applying the Federal Aviation Administration’s System for assessing Aviation’s Global Emissions (SAGE), Version 1.5, to evaluate global aircraft fuel consumption and emissions. The model is capable of computing fuel burn and emissions on a flight-by-flight, fleet and global basis. Here, a parametric study was conducted to rank-order the effects that the modeling uncertainties had on estimates of fuel burn and emissions. Statistical methods were applied to analyze both the random and systematic errors of the model. Also, applying the model to a sample policy analysis case allowed an examination of more stringent engine certification standards for mitigating aviation emissions. Uncertainties of the model were carefully accounted for in the fuel burn and emissions scenarios of the policy options. Results show that for some applications, SAGE may be used to resolve small differences in fleet emissions performance. Although the absolute uncertainty in flight-by-flight NO_x predictions from the model are of the order of 40%, results show that it is well within the current capabilities of the model to distinguish between the fleet average NO_x emissions associated with the typical NO_x stringency options considered in policy analyses.