Numerical Analysis of Mass Emission Measurement Systems for Low Emission Vehicles

Inoué, Kaori; Ishihara, Masaaki; Akashi, Kotaro; Adachi, Masayuki; Ishida, K.

doi:10.4271/1999-01-0150

Cited by 26 publications

(8 citation statements)

References 7 publications

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“…Water condensation is considered to be a common issue in the CVS and has influence on the DF calculation. 9–12 A frequent solution is to heat the raw exhaust transfer tubing and CVS system ductwork. However, compared to the magnitude of the CO 2 difference exhibited here, the DF error from the water condensation does not have a significant influence on the CO 2 measurement.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of the constant volume sampler on plug-in hybrid electric vehicle cold start emission testing

Zhang

Brown

Samuelsen

2013

International Journal of Engine Research

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Previous study shows that the constant volume sampler incorrectly measures some of the exhaust gas when testing a plug-in hybrid electric vehicle in the cold start condition when comparing the CO 2 results from constant volume sampler and fuel flow meter. The main reason is likely associated with the exhaust left in the vehicle tailpipe and constant volume sampler sampling line. Other factors, such as fuel line expansion and water condensation in the exhaust system, are also considered to have contributions. This article evaluates these issues quantitatively by testing a Toyota Prius hybrid electric vehicle on the industry standard constant volume sampler system combined with both a fuel flow meter measurement and an electronic control unit record for fuel consumption. Cold start test cycles and test cycles with a system pre-purge event show that the constant volume sampler has a significant delay in measuring the exhaust, and the estimated exhaust losses for the test car are 15 g CO 2 . Tests with a purge event at the end of the driving cycle show that there are approximately 7 g of CO 2 trapped in the exhaust system and the constant volume sampler sampling line, and the possible reasons for the discrepancy of the above two points (15 and 7 g) are evaluated. The expansion and air bubble influence the fuel flow meter, and the impact of water condensation on CO 2 and CO appears to be negligible.

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Section: Resultsmentioning

confidence: 99%

Evaluation of the constant volume sampler on plug-in hybrid electric vehicle cold start emission testing

Zhang

Brown

Samuelsen

2013

International Journal of Engine Research

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“…The water condensation at the tailpipe has been observed by some researchers [17,20]. The low H 2 O concentration at the beginning of a cold start test is something that has been seen [19], but no special attention has been given as until recently measurements from the tailpipe were not required by the legislation.…”

Section: Discussionmentioning

confidence: 99%

Exhaust Gas Condensation during Engine Cold Start and Application of the Dry-Wet Correction Factor

2019

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Gas components, like carbon monoxide (CO) and dioxide (CO2), can be measured on a wet- or dry-basis depending on whether the water is left or removed from the sample before analysis. The dry concentrations of gaseous components in the exhaust from internal combustion engines are converted to wet concentrations with conversion factors based on the combustion products and the fuel properties. Recent CO2 measurements with portable emissions measurement systems (PEMS) compared to laboratory grade equipment showed differences during the first minutes after engine start. In this study we compared instruments measuring on a dry- and wet-basis using different measuring principles (non-dispersive infrared detection (NDIR) and Fourier-transform infrared spectroscopy (FTIR)) at the exhaust of gasoline, compressed natural gas (CNG), and diesel light-duty and L-category vehicles. The results showed an underestimation of the CO2 and CO mass emissions up to 13% at cold start when the conversion factor is applied and not direct “wet” measurements are taken, raising concerns about reported CO2 and CO cold start emissions in some cases. The underestimation was negligible (<1%) for CO2 when the whole test (20–30 min) was considered, but not for CO (1%–10% underestimation) because the majority of emissions takes place at cold start. Exhaust gas temperature, H2O measurements and different expressions of the dry-wet corrections confirmed that the differences are due to condensation at the exhaust pipes and aftertreatment devices when the surface temperatures are lower than the dew point of the exhaust gases. The results of this study help to interpret differences when comparing instruments with different principles of operation at the same location, instruments sampling at different locations, or the same instrument measuring different driving test cycles or at different ambient temperatures (e.g., −7 °C).

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“…In the 1990s, new formulas were developed for the exhaust gas dilution factor, which eliminated the primary sources of errors in determining DF using Equation (2) [4][5][6][7]. In [8] shown the results of a comparison of dilution factor (DF) and dilution ratio (DR) depending on the different values of the air-fuel ratio.…”

Section: Introductionmentioning

confidence: 99%

“…Thanks to this, the error resulting from the method of determining the DF factor becomes negligible. In order to remove pollutants from the dilution air, exhaust gas sampling systems of the DAR-CVS type are used [6,9,10]:…”

Section: Introductionmentioning

confidence: 99%

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The Issues of the Air-Fuel Ratio in Exhaust Emissions Tests Carried out on a Chassis Dynamometer

Gis¹,

Taubert²

2021

Energies

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Vehicle exhaust emission tests use exhaust sampling systems that dilute the exhaust gas with ambient air. The dilution factor DF is calculated assuming that the combustion is complete, and that the engine is operated at a stoichiometric air-fuel ratio (AFR). These assumptions are not always met. This is especially true for diesel engines. This article discusses the tests to find out what the average lambda (λ) over the ARTEMIS, WLTC and NEDC driving cycles is and how this affects the result of the emission measurements. Measurements were carried out on a chassis dynamometer equipped with a standard emission measurement system used during the homologation. The λ was calculated using the Brettschneider equation. The dilution ratio DR was also determined by measuring the CO2 concentration in the raw exhaust gas. The CO2-tracer method used for this was modified. The median of the λ for a CI vehicle was 1.23–3.31, which makes the relative percentage difference between the DF and DR (DDF) in the range of 28–167%. For a SI vehicle homologated under the WLTP procedure, the median of the λ for the WLTC and ARTEMIS cycles was close to one and DDF for most cycles does not exceed 10%. In order to reduce the influence of the error of DF determination on the result of the emission measurement, it is recommended to use exhaust gas sampling systems that allow to determine the actual dilution ratio or to use the lowest possible dilution. The PAS-CVS system seems to be the most promising.

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Numerical Analysis of Mass Emission Measurement Systems for Low Emission Vehicles

Cited by 26 publications

References 7 publications

Evaluation of the constant volume sampler on plug-in hybrid electric vehicle cold start emission testing

Evaluation of the constant volume sampler on plug-in hybrid electric vehicle cold start emission testing

Exhaust Gas Condensation during Engine Cold Start and Application of the Dry-Wet Correction Factor

The Issues of the Air-Fuel Ratio in Exhaust Emissions Tests Carried out on a Chassis Dynamometer

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