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Controlling NOx and CO2 emissions from heavy-duty diesel vehicles (HDDVs) is receiving increasing attention. Accurate measurement of HDDV NOx and CO2 emissions is the prerequisite for HDDV emission control. Vehicle emission regulations srecommend the measurement of NOx and CO2 emissions from vehicles using an emission analyzer, which is expensive and unsuitable to measure a large number of vehicles in a short time. The on-board diagnostics (OBD) data stream of HDDVs provides great convenience for calculating vehicle NOx and CO2 emissions by providing the engine fuel flow rate, NOx sensor output, and air mass flow. The calculated vehicle NOx and CO2 emissions based on the OBD data were validated by testing a heavy-duty truck's emissions on the chassis dynamometer over the CHTC-HT driving cycle, showing that the calculated NOx and CO2 emissions based on the OBD data are consistent with the measured results by the emission analyzer. The calculated vehicle fuel consumptions based on the OBD data were close to the calculated results based on the carbon balance method and the measured results by the fuel flowmeter. The experimental results show that accessing vehicle NOx and CO2 emissions based on the OBD data is a convenient and applicable method. [ABSTRACT FROM AUTHOR]

China implemented the China VI emission standard in 2020. The China VI emission standard has added requirements for the RDE (real-world driving emission) test. To evaluate vehicle CO2 emission for different vehicles, 10 conventional gasoline vehicles were tested under the RDE procedure using the PEMS (portable emission testing system) method. All vehicles tested meet the sixth emission regulation with a displacement of 1.4 L~2.0 L. Among the vehicles tested, the highest CO2 emission factor was 281 g/km and the lowest was 189 g/km, while the acceleration of RDE gets a wider distribution, varying from −2.5 m/s2 to 2.5 m/s2. The instantaneous mass emission rate could reach around 16 g/s. The amounts of total CO2 emission in the positive region and the negative region make up 82~89% and 11~18% of the overall CO2 emission during the entire RDE driving period, respectively. The same vehicle has a wide range of CO2 emission factors at different VSP (vehicle specific power) intervals. Different RDE test conditions can lead to large differences in CO2 emissions. [ABSTRACT FROM AUTHOR]

Remote sensing technology has been used for gasoline vehicle gaseous emissions monitoring for nearly 30 years. However, the application effect of the remote sensing detection of diesel vehicle tailpipe emission concentrations is unsatisfactory. Therefore, several approaches were proposed to analyze the remote sensing results for gaseous exhaust emissions from diesel vehicles, including the concentration ratios of gaseous emission components to carbon dioxide (CO2) and fuel-based emission factors. Based on our experimental results, these two metrics have some high values in low-speed or low-load conditions of vehicles, which introduces uncertainty when evaluating vehicle emission levels. Therefore, an inversion calculation method originally developed for remote sensing light duty diesel vehicle gaseous emissions was used for the remote sensing of nitrogen monoxide (NO) tailpipe concentrations in heavy duty diesel vehicles, and validated by PEMS tested emission results. For the first time, the above three options for evaluating the NOx emission level of diesel vehicles, including the concentration ratio of NO to CO2, the fuel-based NO emission factor and the estimated tailpipe NO emission concentration were investigated, and some influencing factors were also discussed. The remote sensing tailpipe NO emission concentration can be directly used to evaluate diesel vehicle NO emission levels compared with the two other metrics. [ABSTRACT FROM AUTHOR]

• NG fueling emitted initially lower CO but higher THC and NOx emissions than gasoline. • Emission deteriorated faster in NG mode due to poor calibration and regulation flaws. • NG fueling reduced 20 % CO2 but the GWP benefit was partially offset by fuel leakage. Natural gas (NG) is considered an economically viable transport decarbonization option, especially for developing countries. However, as per the ongoing European and Chinese vehicle emission regulations, the durability and in-service compliance tests of the exhaust emissions from gasoline/NG bi-fuel vehicles are only mandated in gasoline mode, leaving the real-world emission performance of NG fueling at risk. To bridge this gap, the exhaust emissions from five gasoline/NG bi-fuel taxis were traced from new (less than 10,000 km) to 160,000 km after every 10,000 km of field driving. Both room-temperature cold-start and warm-start chassis dynamometer tests were performed over the certification drive cycle. This tracing study lasted for 3.5 years and covered the variations of seasons, routine services, and minor repairs. The results manifested that compared to gasoline fueling, NG had statistically lower carbon monoxide before 100,000 km of driving but higher total hydrocarbon and nitrogen oxides emissions throughout the useful life in both cold- and warm-start tests. By applying linear regression to the data points obtained across the 160,000 km tracing, NG fueling showed a noticeably quicker deterioration with mileage than gasoline. However, given that gasoline and NG modes shared the same catalysts, this is attributed to the less careful calibration of NG mode predominantly because of the void of regulatory requirements. On average, NG fueling produced about 20 % less carbon dioxide emissions than gasoline, but the observed fuel leakage in NG mode partially offset the global warming potential advantage. Overall, NG sees benefits and challenges in mitigating vehicle-related environmental issues. To better control this risk, it is strongly recommended that in future regulations, the durability and in-service compliance requirements of NG fueling shall be complemented, and fuel leakage shall be included in the control of evaporative emissions. [ABSTRACT FROM AUTHOR]

• How load and temperature affect CO 2 emission was quantified. • Resistance is the dominant reason for the increased CO 2 emission at cold condition. • Correlation (R2 > 0.93) was found between cumulated CO 2 and transient CO 2 rate. • Correlation (R2 = 0.98) was found between ambient temperature and transient CO 2 rate. • Vehicles achieved a quick warm-up at −10 ℃ than 0 ℃. Vehicle CO 2 emissions have been long studied, but the relationship between ambient temperature and CO 2 emission has never been quantified. To quantitatively evaluate the correlation between ambient temperature and CO 2 emission, two light-duty gasoline vehicles were tested over WLTC (Worldwide-harmonized Light vehicles Test Cycle) under four temperatures, −10 ℃, 0 ℃, 23 ℃, and 40 ℃. Obtained results proved that the dominant reason for the increased CO 2 emission under cold ambient temperature is the increased internal resistance rather than fuel enrichments. CO 2 emission from large engines is more sensitive to temperature variation while that from small engines are more sensitive to load variation. The usage of the air-conditioner increased the distance-specific CO 2 emission by 23.07% and 22.49% for vehicle 1 and vehicle 2 respectively. The strong correlation (R2 greater than 0.98) between cumulated CO 2 emission/coolant temperature and transient CO 2 emission means the cumulated CO 2 emission/coolant temperature could be used to describe the engine warm-up status and to improve the transient CO 2 model. For the laboratory tests, using the coolant temperature to describe the engine warm-up needs more verification due to the uneven engine temperature field. This study helps understand the CO 2 emission at various temperatures and the results in this study could be used for microscopic CO 2 modeling & CO 2 -related regulations. [ABSTRACT FROM AUTHOR]

PHEVs (Plug-in hybrid electric vehicles) are thought to be energy and environment friendly, while these conclusions are seldom verified during real driving tests. To evaluate PHEV real driving energy consumption, CO 2 emission, and pollutants emission, one parallel PHEV was tested under real driving condition. The results indicate that the distance-specific energy consumption of CD (charge depleting) mode, compared with the CS (charge sustaining) mode, is 45% lower for WTW (Well to Wheel) evaluation. The CD WTW CO 2 emission is 50% higher than the CS due to the electricity generation CO 2 intensity. CD and CS mode could have similar CO 2 emission when electricity CO 2 intensity reaches 397.50 g/kWh. The limited charging reduced the PHEV energy conservation by around 50%, but the WTW CO 2 emission is also reduced. Contrary to common belief, the PHEV CD mode real driving emission is underestimated, and it could be over 30 times higher than the CS mode. The deteriorated CD emission is caused by the inaccurate power demand prejudgments and frequent engine cold high-power re-start. The driving pattern comparison reveals that the deteriorated CD emission should not be a local but global concern. These results could be used for PHEV propulsion strategy optimization and test cycle design. • CD WTW energy consumption (1.39 ± 0.06 MJ/km) is 45% lower than CS (2.52 ± 0.07 MJ/km). • CD WTW CO 2 emission (228.74 ± 9.92 MJ/km) is 49% higher than CS (153.59 ± 4.51 MJ/km). • CD and CS modes get similar CO2 emission with electricity CO2 intensity at 397.5 g/kWh. • Compared to CS mode, significantly deteriorated emission under CD mode is confirmed. [ABSTRACT FROM AUTHOR]

• 21 vehicles were tested in six cities with altitudes varying from 26.7 m to 2264.7 m. • Both CO 2 and pollutant emissions get inconsistent results. • The air-fuel ratio and engine operation variation could explain inconsistent results. • The conclusions about altitude based on single vehicle/engine tests are unreliable. • The conformity factor and the extended factors should be tightened. How altitudes affect vehicle CO 2 /pollutant emission has long been studied, while different, sometimes conflicting conclusions are reported. To evaluate how altitudes impact vehicle CO 2 /pollutant emission, 21 vehicles were tested in six cities with altitudes ranging from 26.7 m above sea level (masl) to 2264.7 masl. Three of the vehicles were tested in the altitude chamber at five different heights (from 0 to 2400 masl) following the Worldwide Harmonized Light Vehicles Test Procedure (WLTP). CO 2 /pollutant emissions, conformity factor, and extended factor were evaluated based on the results obtained. No uniform patterns were found between altitudes and CO 2 /pollutant emission in both laboratory and real driving tests. For laboratory tests, the different CO 2 emission results could be explained by air-fuel ratio variations during the transient cycles and engine operation variations between tests. More variables were introduced to the real driving tests, which brings more uncertainty to the CO 2 emission. The average CO 2 emission of the turbocharged and naturally aspirated vehicles at various cities share similar patterns, indicating other parameters (e.g., driving patterns, road conditions, ambient conditions, et al.) might have a larger impact on the CO 2 emission than the altitude growth. These reasons could account for the irregular pollutant results. Besides, the cylinder-to-cylinder variations in equivalence ratio about the mean value have more enormous impacts on the emission results. Discrete results mean that single engine/vehicle tests couldn't reflect the real situations at various heights. The current conformity factors and the extended factors might be too loose. [ABSTRACT FROM AUTHOR]