Transient Emissions Research Articles

Proton‐transfer‐reaction time‐of‐flight mass spectrometry (PTR‐TOF‐MS) as a tool for studying animal volatile organic compound (VOC) emissions

Abstract Chemical sensing in vertebrates is crucial in their lives, and efforts are undertaken towards deciphering their chemical language. Volatile organic compounds (VOCs) are a group of chemicals believed to play an essential role in a wide variety of animal interactions. Therefore, understanding what animals sense themselves and untangling the ecological role of their volatile cues can be accomplished by analysing VOC emissions. A proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐TOF‐MS) is an instrument that measures VOCs in real‐time in an air sample. Since this technique acts as a hyper‐sensitive ‘nose’ it has a similar potential in deciphering the chemical language of vertebrates. Here, we validate the use of PTR‐TOF‐MS as a tool to measure VOCs from vertebrates, which in turn will help resolve vertebrate interactions through VOCs. The instrument monitors and records the full spectrum of VOCs emitted by an individual with a high accuracy and low detection limit, including transient VOC emissions. We propose and test diverse measuring configurations that allow for measurement of VOC emissions from different vertebrates and their exudates: full body, specific parts of the body, urine and femoral pores. In addition, we test configurations for sudden and short‐lasting processes as VOCs emitted during adder skin shedding as well as the emissions of skin secretions upon mechanical and physiological stimulation in amphibia. Our configurations work in tandem with gas chromatography–mass spectrometry (GC‐MS) to allow compound structure verification. We discuss the configurations and methodologies used and conclude with recommendations for further studies, such as the choice of chamber size and flow. We also report the results of the measurements on vertebrates—that are novel to science—and discuss their ecological meaning. We argue that PTR‐TOF‐MS has a high potential to resolve important unanswered questions in vertebrate chemical ecology with great adaptability to a wide range of experimental set‐ups. If combined with a structure verification tool, such as GC‐MS, the creative deployment of PTR‐TOF‐MS in various future study designs will lead to the identification of ecologically relevant VOCs.

Measurement of cycle-resolved engine-out soot concentration from a diesel-pilot assisted natural gas direct-injection compression-ignition engine

Exhaust-stream particulate matter (PM) emission from combustion sources such as internal combustion engines are typically characterized with modest temporal resolutions; however, in-cylinder investigations have demonstrated significant variability and the importance of individual cycles in transient PM emissions. Here, using a Fast Exhaust Nephelometer (FEN), a methodology is developed for measuring the cycle-specific PM concentration at the exhaust port of a single-cylinder research engine. The measured FEN light-scattering is converted to cycle-resolved soot mass concentration ([Formula: see text]), and used to characterize the variability of engine-out soot emission. To validate this method, exhaust-port FEN measurements are compared with diluted gravimetric PM mass and scanning mobility particle sizer (SMPS) measurements, resulting in close agreements with an overall root-mean-square deviation of better than 30%. It is noted that when PM is sampled downstream in the exhaust system, the particles are larger by 50–70 nm due to coagulation. The response time of the FEN was characterized using a “skip-firing” scheme, by enabling and disabling the fuel injection during otherwise steady-state operation. The average response time due to sample transfer and mixing times is 55 ms, well below the engine cycle period (100 ms) for the considered engine speeds, thus suitable for single-cycle measurements carried out in this work. Utilizing the fast-response capability of the FEN, it is observed that cycle-specific gross indicated mean effective pressure (GIMEP) and [Formula: see text] are negatively correlated ([Formula: see text]: 0.2–0.7), implying that cycles with lower GIMEP emit more soot. The physical causes of this association deserve further investigation, but are expected to be caused by local fuel-air mixing effects. The averaged exhaust-port [Formula: see text] is similar to the diluted gravimetric measurements, but the cycle-to-cycle variations can only be detected with the FEN. The methodology developed here will be used in future investigations to characterize PM emissions during transient engine operation, and to enable exhaust-stream PM measurements for optical engine experiments.

Hearing screening in schoolchildren: accuracy of different criteria used to analyze transient evoked otoacoustic emissions

ABSTRACT Purpose: to compare the accuracy of different criteria used to analyze transient evoked otoacoustic emissions in schoolchildren. Methods: an accuracy study, where an audiological assessment (audiometry, logoaudiometry, tympanometry) and transient emissions were performed with 70 schoolchildren, from the first to the fifth grade of a municipal school, in Northeastern Brazil (6-14 years, 9.9 ± 2 years), with four criteria, all with signal-to-noise ratio ≥ 3 dB, being: criterion A, in all frequency bands; B, in three consecutive frequency bands; C, in three of the five non-consecutive frequency bands; D, in 2, 3 and 4 kHz. Sensitivity, specificity, accuracy and predictive values with their respective confidence intervals of 95% were analyzed. Results: criterion A showed higher sensitivity (92.31%, 95% CI: 67-98%) and lower specificity (17.35%, 95% CI: 10-29%); criterion C higher specificity (84.21%, 95% CI: 72-91%) and higher positive predictive value (52.63%; 95% CI: 51.63-54.63). Accuracy was 82.85% (95% CI 78.23-87.47) in criterion C and 70% (95% CI: 65.38-74.62) in criterion B. Conclusion: criterion C, signal-to-noise ratio ≥ 3dB in three non-consecutive frequency bands, showed the best accuracy, being considered the best choice as a criterion for the isolated use of transient emissions as a hearing screening procedure, in schoolchildren.

Absorbing aerosols over Asia – an inter-model and model-observation comparison study using CAM5.3-Oslo

Aerosol absorption constitutes a significant component of the total radiative effect of aerosols, and hence its representation in general circulation models is crucial to radiative forcing estimates. We use here multiple observations to evaluate the performance of CAM5.3-Oslo with respect to its aerosol representation. CAM5.3-Oslo is the atmospheric component of the earth system model NorESM1.2 and shows on average an underestimation of aerosol absorption in the focus region over East and South Asia and a strong aerosol absorption overestimation in desert and arid regions compared to observations and other AeroCom phase III models. We explore the reasons of the model spread and find that it is related to the column burden and residence time of absorbing aerosols, in particular black carbon and dust. We conduct further sensitivity simulations with CAM5.3-Oslo to identify processes which are most important for modelled aerosol absorption. The sensitivity experiments target aerosol optical properties, and contrast their impact with effects from changes in emissions and deposition processes, and the driving meteorology. An improved agreement with observations was found with the use of a refined emission data set, transient emissions and assimilation of meteorological observations. Changes in optical properties of absorbing aerosols can also reduce the under- and overestimation of aerosol absorption in the model. However, changes in aerosol absorption strength between the sensitivity experiments are small compared to the inter-model spread among the AeroCom phase III models.

A Novel Deep Learning Approach to Predict the Instantaneous NOₓ Emissions From Diesel Engine

Accurate and stable prediction of NOx emissions from diesel vehicles plays a crucial role in the establishment of virtual NOx sensors and the development and design of diesel engines. This paper presents a method for estimating transient NOx emissions by complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and a long- and short-term memory neural network (LSTM). First, the CEEMDAN algorithm is used to reduce the non-stationarity and volatility of the transient NOx emission data to obtain multiple subseries with different frequencies. Secondly, a predictive model is developed for each subsequence using an LSTM neural network. Finally, the results of each subsequence prediction are summed to obtain the final prediction. The proposed model uses NOx emission data generated by an EU IV diesel bus during real road driving. The results show that (1) The use of CEEMDAN can effectively improve the smoothness of NOx transient emission data, as well as facilitate more effective extraction of internal characteristics and variations of the raw data. (2) LSTM has better learning and prediction capability for transient changes in NOx emissions. (3) The results of CEEMDAN-LSTM for RMSE, R2, MAE and NRMSE are 46.11,0.98, 29.82 and 2.71, respectively, which are better than the other model with improved prediction performance.

Thermal assistance in the optically stimulated luminescence of superluminous Sr4Al14O25: Eu2+,Dy3+

The thermally induced increase in optically stimulated luminescence of super-luminous Sr4Al14O25:Eu,Dy is reported. To isolate this thermal assistance to emission, which is otherwise obscured by high intensity transient emissions, stimulation was done using 870 nm infrared light. The optically stimulated luminescence intensity measured between 20 and 200 °C goes through a peak. The profile is reproducible and is independent of whether the measurements are made with the temperature increasing or decreasing. The initial increase in signal is ascribed to thermal assistance and the subsequent decrease is due to thermal quenching. The activation energy of thermal assistance was determined as 0.30±0.01 eV. The corresponding value for the activation energy for thermal quenching is also reported as are methods for determining these parameters from the temperature dependence of the luminescence. The thermal assistance effect is explained with reference to a configurational coordinate model.

For cleaner exhaust of a high performance motorcycle: A macroscopic comparative study of catalytic converters under world-wide motorcycle test cycle

Considering the noble metals resources used in Three-way catalysts are extremely limited, traditional Three-way catalysts can no longer meet the increasingly stringent emissions control standards economically. For more efficient emissions control, we first time to perform a multi-parameters comparative investigation on catalytic converter design for high performance motorcycles with considerations of converter’s structure/size, layout and engine working status under World-wide Motorcycle Test Cycle to explore novel design methods of Three-way catalysts. Based on the several models designed for test, the original transient emissions are measured to explore engine’s working performances and factors that impact raw emissions, the integrated effect of converter structure/size and layout on emissions conversion efficiency is also explored. In this study, Model 1 is double catalytic structure while Model 2 and Model 3 are single structure, detailed parameters about these models are expressed as the format “Length, Diameter or long/short axis for ellipse, Cell density” as: Model 1-front: 42 mm, 123 mm, 200 cpsi; Model 1-rear: 123 mm, 95/65 mm, 300 cpsi; Model 2: 85 mm, 100 mm, 400 cpsi; Model 3: 82 mm, 130 mm, 300 cpsi. Catalytic conversion efficiency of CO, THC and NOx are ranked as Model 3: 88.13% > Model 1: 85.95% > Model 2: 84.89%, Model 1: 93.73% > Model 3: 89.76% > Model 2: 85.79% and Model 1: 98.27% > Model 2: 92.58% > Model 3: 87.05%, respectively. Small-size catalytic converters have quicker warm-up and poorer heat preservation capacity, that’s why Model 2 has the highest catalytic efficiency for CO in cold stage and the lowest overall, Meanwhile, Model 2 has the best trade-off performance. We hope to provide useful knowledge that guides the converter design/application.

Audiovestibular Quantification in Rare Third Window Disorders in Children.

Third window disorders are structural abnormalities in the bony otic capsule that establish a connection between the middle/inner ear or the inner ear/cranial cavity. Investigated extensively in adults, they have hardly been studied in children. This study is a retrospective study of children (aged 5–17 years) diagnosed with rare third window disorders (third window disorders reported rarely or not reported in children) in a tertiary pediatric vestibular unit in the United Kingdom. It aimed to investigate audiovestibular function in these children. Final diagnosis was achieved by high resolution CT scan of the temporal bones. Of 920 children attending for audiovestibular assessment over a 42 month period, rare third windows were observed in 8 (<1%). These included posterior semicircular canal dehiscence (n = 3, 0.3%), posterior semicircular canal thinning (n = 2, 0.2%), X linked gusher (n = 2, 0.2%), and a combination of dilated internal auditory meatus/irregular cochlear partition/deficient facial nerve canal (n = 1, 0.1%). The majority of them (87.5%) demonstrated a mixed/conductive hearing loss with an air-bone gap in the presence of normal tympanometry (100%). Transient otoacoustic emissions were absent with a simultaneous cochlear pathology in 50% of the cohort. Features of disequilibrium were observed in 75% and about a third showed deranged vestibular function tests. Video head impulse test abnormalities were detected in 50% localizing to the side of the lesion. Cervical vestibular evoked myogenic potential test abnormalities were observed in all children in the cohort undergoing the test where low thresholds and high amplitudes classically found in third window disorders localized to the side of the defects in 28.5%. In the series, 71.4% also demonstrated absent responses/amplitude asymmetry, some of which did not localize to the ipsilesional side. Two children presented with typical third window symptoms. This study observes 2 new rare pediatric third window phenotypes and the presence of a cochlear hearing loss in these disorders. It emphasizes that these disorders should be considered as an etiology of hearing loss/disequilibrium in children. It also suggests that pediatric third window disorders may not present with classical third window features and are variable in their presentations/audiovestibular functions.

The experimental study on transient emissions and engine behaviors of a sporting motorcycle under World Motorcycle Test Cycle

In this study, the THC, CO/CO2 and NOx emissions were investigated by experimental measurements on a twin-spark sporting motorcycle under real-world driving. The emissions at two typical engine steady-state operating points were also added for comparison. Meanwhile, the engine working status was monitored during the whole trip. The results indicate that the small throttle opening and the rich air/fuel ratio make the very low engine combustion efficiency during cold-start phase, which leads to higher THC and CO emissions. During this stage, the CO2 is also high due to the absolutely high fuel consumption rather than the high combustion efficiency, due to the low NOx emission. By comparing this studied engine to others, the direction to improve the transient response especially under low loads was found. Compared with steady-state operation, both CO and CO2 during transient driving are lower, because at transient driving the combustion temperature is lower, leading to lower products amounts for those CO precursor (especially for HCO). The lower combustion temperature also leads to lower NOx emission, and the incomplete combustion leads to higher THC emission at cycle driving. In a word, the lower volume efficiency and delay ignition timing result in poorer combustion status during transient driving.

Otoacoustic emissions: major trends in pediatric practice

The high prevalence of hearing loss in children determines the need for reliable methods for the timely detection and diagnosis of hearing impairment at any age, starting from a birth. Otoacoustic emissions are widely used in hearing screening and audiological assessment as an objective tool for cochlear status evaluation. Over the past 30 years, their use in routine audiological assessments has increased significantly. Understanding the subtle processes that occur in the cochlea during the transmission of acoustic stimuli which generate otoacoustic emissions as well as knowledge about the registration parameters, otoacoustic emissions characteristics, otoacoustic emissions advantages and constraints are important for results analysis. Contemporary understanding of the occurrence of auditory sensations as well as the description of various types of otoacoustic emissions used in routine clinical practice (transient otoacoustic emissions and distorting product otoacoustic emissions) are presented in the review. The features of otoacoustic emissions using in pediatric practice are described: in newborns hearing screening, including the peculiarities of applying of this test for infants having had got their treatment in the intensive care units. Otoacoustic emissions significance for hearing diagnosis and as well as for ototoxicity monitoring is shown. Reliability, non-invasiveness, objectivity, simplicity of the otoacoustic emissions testing has done it one of the main methods both in hearing screening and diagnostics for children on any age.

A comparative experimental study on emission characteristics of a turbocharged gasoline direct-injection (TGDI) engine fuelled with gasoline/ethanol blends under transient cold-start and steady-state conditions

In this study, the emissions of a TGDI engine were experimentally investigated and compared under transient cold-start operating and steady-state operating conditions, respectively. Furthermore, the steady-state emissions of the TGDI engine under different coolant out temperature (43 °C, 65 °C, 88 °C, 102 °C and 110 °C) were compared to the transient emissions. The results indicated that the transient NOx emissions and the steady-state NOx emissions were strongly depended on the load of the TGDI engine. Moreover, under steady-state operating conditions, the NOx emissions of the TGDI engine were increased with the coolant temperature from 43 °C to 102 °C, while the NOx emissions were decreased at the outlet coolant temperature of 110 °C due to retard the spark timing. Apart from that, the HC emissions under transient cold-start condition were approximately ten times than that of the steady-state conditions. Under steady-state operating conditions, the HC emissions were basically decreased with the coolant temperature from 43 °C to 110 °C due to reduction of the flame quenching distance. The excess air ratio of the TGDI engine slightly fluctuated around stoichiometric air/fuel ratio under the NEDC, while the excess air ratio was literally off the charts during the deceleration operating conditions due to the fuel cut-off. CO emission periodically reached a peak value at deceleration operating conditions under transient cold start condition, while CO emission was much high at the high-load and high-speed regions under steady-state operating conditions. In addition, the outlet coolant temperature did not present an obvious effect on the CO emission formation.

The Measurement of Fast Transient Emissions During Real World Driving

Some of the most challenging aspects of preparing vehicles to comply with the new RDE (Real Driving Emissions) legislation are the calibration of engines to minimize emissions during numerous short lived transients. Fast response emissions analyzers are necessary to resolve rapid transient emissions and have been deployed simultaneously in the engine-out and tailpipe exhaust gas stream of several vehicles. The methodology presented and capability of the instrumentation enables fine resolution of emissions events leading to the opportunity for fine tuning of controller performance. Data has also been logged from the vehicles' ECUs and combined with accurate GPS data. The results show that certain road lay-outs (e.g., congested junctions and speed bumps) can provoke significant tailpipe NOx emissions; often emitting very high levels near schools where traffic calming measures have been adopted for road safety. The lean excursions and insufficient rich purge during such transients are generally shown to be the cause of such emitting events.

Brainstem auditory pathway of children with acute lymphoid leukemia on chemotherapy with methotrexate.

Investigate the auditory pathway in the brainstem of children with acute lymphoblastic leukemia submitted to chemotherapy (by intravenous or intrathecal infusion). Fourteen children aged between 2 and 12 years with diagnosis of acute lymphoid leukemia were evaluated. The following procedures were used: meatoscopy, acoustic immitance measurements, tonal audiometry, vocal audiometry, transient otoacoustic emissions, and auditory brainstem response. From the 14 children with normal auditory thresholds, 35.71% showed an alteration in auditory brainstem response, with a predominance of hearing impairment in the lower brainstem. It was found that 80% of the children with alteration had used intrathecal methotrexate less than 30 days and that 40% had the highest cumulative intravenous methotrexate doses. Children with acute lymphoblastic leukemia submitted to chemotherapy, present auditory pathway impairment in the brainstem, with a predominance of a low brainstem.

Transient otoacoustic emissions analysis by frequency bands in adolescents with type 1 diabetes mellitus

Transient otoacoustic emissions analysis by frequency bands in adolescents with type 1 diabetes mellitus

Audiological profile of indoor cycling teachers

ABSTRACT Purpose: to describe the audiological profile and auditory complaints of indoor cycling teachers, as well as to relate the findings with time of noise exposure and presence of tinnitus. Methods: participants were eight teachers of both genders, age ranging from 24 to 36 years, with professional experience in the area for at least one year. Sound pressure level was measured during the class, which lasted from 45 to 50 minutes and an adapted anamnesis questionnaire composed of ten items was applied to each individual to research the auditory symptoms and factors related to noise exposure and the audiological assessment performed. Inferential statistical tests were applied. The level of statistical significance was 0.05. Results: all of them had pure tone audiometry, tympanometry testing and brainstem auditory evoked potential within normal limits. There were alterations in the high frequency audiometry and otoacoustic emissions without a statistical correlation with the time of professional experience. Conclusion: the audiological profile obtained was pure tone audiometry, tympanometry and brainstem auditory evoked potential within normal limits; altered transient otoacoustic and distortion product emissions and high frequency audiometry. The complaints reported were: tinnitus, dizziness, the need to listen at a high volume and being exposed to excessive noise.

A laboratory approach to CO2 and CO emission factors from underground coal fires

Carbon emissions from underground coal fires (UCF) have become an emerging research topic and their role in global climate warming has been widely debated. Currently, one big uncertainty for assessing UCF's carbon emission is the hypothesized carbon emission factors (EF) from the complete combustion of coal, while the EF of smoldering combustion of coal in the context of UCF is still unknown yet. In this work, a 1/20 scale laboratory experimental framework was proposed to characterize transient carbon emissions and quantify EFCO2 and EFCO. Effects of fire depth, ventilation area (aperture size), and coal rank on carbon emissions were explored with the extrapolation to the full-scale UCF. Results showed that total carbon emissions increase with the carbon content of coal. Volatile content is an important factor impacting the burning behavior and gas emission. Stable EFCO2 and EFCO of UCF, independent of the fire depth and aperture size, were estimated as 2006 ± 36 g kg−1 and 345 ± 132 g kg−1, respectively; its combustion efficiency was 85% ± 3%. The extrapolation of experimental data estimates the CO2 emission of coal fires in China and the USA as 2.34 × 107–4.61 × 107 t yr−1, which accounted for 0.4% - 0.9% of total CO2 emissions in the world in 2016.

Haze emissions from smouldering peat: The roles of inorganic content and bulk density

Smouldering peat fires are reported across continents and their emissions result in regional haze crisis (large scale accumulation of smoke at low altitudes) and large carbon foot prints. Inorganic content (IC) and bulk density vary naturally in peatlands and are among the important parameters governing peat fires. However, their roles in fire emissions remain unknown. In this work, bench-scale burning of sphagnum peat conditioned to different values of IC and bulk densities were conducted in the laboratory environment. Mass loss rate, spread rate and transient emissions of 20 gas species and particles (PM10, PM2.5 and PM1) were simultaneously investigated. We found that peat with 50% moisture content can self-sustain smouldering propagation if IC is less than 40%, or its bulk density is lower than 287.5 kg m−3. Increasing IC or bulk density decreases peat mass loss rate and spread rate. High IC peat releases lower gas fluxes (especially for CH4 and NH3) throughout the experiment. In the ignition stage, increasing IC leads to an increase in particles with diameter between 1 and 2.5 μm; in the fire spread stage, IC has no influence on the particle fluxes. In contrast, increasing bulk density delays both gas and particle emission fluxes without altering the smoke composition significantly. The fundamental understanding of how soil properties affect peat wildfires facilitates the development of mitigation technologies against haze.

Dynamic simulation of a vessel drive system with dual fuel engines and energy storage

Dredging operations result in severe load changes, and the transient capability of natural gas-fuelled dual fuel engines in gas mode is not sufficient to cope with them. An energy storage system may compensate the difference depending on the system size and control strategy. Previously developed component models are adapted and expanded with natural gas combustion and a kinetic energy storage system. The dual fuel engine’s performance and transient behaviour in gas mode is validated with data from a factory acceptance test. Both the effect of increasing the available engine power and increasing the power of the energy storage system are investigated. The simulation results show the trade-off between the transient capability and lower harmful emissions on one side, and the operational costs and system efficiency on the other side. Increasing the available engine power, enhances the drive system’s transient capability by reducing load change experienced by each engine, but it also increases the fuel energy consumption and global warming potential. A kinetic energy storage system increases the average engine load and fuel energy consumption slightly. The higher engine load results in a lower methane slip and does, therefore, not result in a net increase of the global warming potential.

A terrestrial gamma-ray flash and ionospheric ultraviolet emissions powered by lightning.

Terrestrial gamma-ray flashes (TGFs) are transient gamma-ray emissions from thunderstorms, generated by electrons accelerated to relativistic energies in electric fields. Elves are ultraviolet and optical emissions excited in the lower ionosphere by electromagnetic waves radiated from lightning current pulses. We observed a TGF and an associated elve using the Atmosphere-Space Interactions Monitor on the International Space Station. The TGF occurred at the onset of a lightning current pulse that generated an elve, in the early stage of a lightning flash. Our measurements suggest that the current onset is fast and has a high amplitude-a prerequisite for elves-and that the TGF is generated in the electric fields associated with the lightning leader.

Assessment of CO2 and NOx Emissions of One Diesel and One Bi-Fuel Gasoline/CNG Euro 6 Vehicles During Real-World Driving and Laboratory Testing

The objective of this study is the assessment of the real-world environmental performance, and the comparison with laboratory measurements, of two Euro 6 passenger cars. The first is equipped with a common-rail diesel engine, Lean NOx Trap (LNT) and Diesel Particulate Filter (DPF), and the second is a bi-fuel gasoline/CNG (Compressed Natural Gas) one, equipped with Three Way Catalyst (TWC). The experimental campaign consisted of on-road and chassis dynamometer measurements. In the former test set, two driving routes were followed, one complying with the Real Driving Emissions (RDE) regulation, and another characterized by more dynamic driving. The aim of the latter route was to go beyond the regulatory limits and cover a wider range of real-world conditions and engine operating area. In the laboratory, the WLTC (Worldwide harmonized Light vehicles Test Cycle) was tested, applying the real-world road load of the vehicles. Both cars underwent the same tests, and these were repeated for the primary (CNG) and the secondary (gasoline) fuel of the bi-fuel vehicle. In all the tests, CO2 and NOx emissions were measured with a Portable Emissions Measurement System (PEMS). The results were analyzed on two levels, the aggregated and the instantaneous, in order to highlight the different emissions attributes under varying driving conditions. The application of the realistic road load in the WLTC limited its difference with the RDE compliant route, in terms of CO2 emissions. However, the aggressive driver behavior and the uphill roads of the Dynamic driving schedule resulted in around double CO2 emissions for both cars. The potential of natural gas to reduce CO2 emissions was also highlighted. Concerning the diesel car NOx emissions, the real-world results were significantly higher than the respective WLTC levels. On the other hand, the bi-fuel car exhibited very low NOx emissions with both fuels. Natural gas resulted in increased NOx emissions, compared to gasoline, always remaining below the Euro 6 limit, with only exception the Dynamic driving schedule. Finally, it was found that the overall cycle dynamics are not sufficient for the complete assessment of transient emissions and the instantaneous engine and aftertreatment behavior can reveal additional details.