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Biogas combustion: chemiluminescence fingerprint

Publication . Quintino, Filipe; Trindade, Teodoro; Fernandes, Edgar C.

A numerical and experimental study was conducted, with the purpose of inferring the influence of the CO2 concentration (xCO2) for different equivalence ratios (ϕ) on CH4/CO2/air (biogas) flames chemiluminescence. A thorough analysis on the signals of OH∗, CH∗, C∗2 and CO∗2 was performed. Typical biogas compositions were tested under laminar atmospheric flame conditions, within the unburned equivalence ratio of 0.9 and 1.14 with CO2 concentrations up to 40% in the blend. Experimental measurements of chemiluminescence were done using spectroscopy in the UV–visible region of the spectra. Simulations were performed with the GRI-Mech 3.0 mechanism without accounting for the nitrogen chemistry, extended with a chemiluminescence kinetics of OH∗, CH∗, C∗2 and CO∗2, in a burner-stabilized frame in CANTERA. Experimental measurements and numerical simulations are compared and generally are in good agreement. It was verified that CO2 dilution leads to a regular decrease in the emission intensities of OH∗, CH∗, C∗2 and CO∗2. Relations between chemiluminescence intensity ratios and xCO2 and ϕ were found. It was shown that OH∗/CO∗2 and C∗2/CO∗2 have the potential predict xCO2 in CH4/CO2/air flames. Moreover, it was verified that OH∗/CH∗, OH∗/C∗2 and CH∗/C∗2 are well suited to infer ϕ for the blends tested. It was verified that xCO2 does not cause relevant changes in the chemiluminescence ratios when inferring ϕ.

2018-11Journal article

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Engine cold start analysis using naturalistic driving data: City level impacts on local pollutants emissions and energy consumption

Publication . Faria, Marta; Varella, Roberto A.; Duarte, Gonçalo; Farias, Tiago L.; Baptista, Patricia

The analysis of vehicle cold start emissions has become an issue of utmost importance since the cold phase occurs mainly in urban context, where most of the population lives. In this sense, this research work analyzes and quantifies the impacts of cold start in urban context using naturalistic driving data. Furthermore, an assessment of the influence of ambient temperature on the percentage of time spent on cold start was also performed. Regarding the impacts of ambient temperature on cold start duration, a higher percentage of time spent on cold start was found for lower ambient temperatures (80% of the time for 0 °C and ~50% for 29 °C). Results showed that, during cold start, energy consumption is >110% higher than during hot conditions while emissions are up to 910% higher. Moreover, a higher increase on both energy consumption and emissions was found for gasoline vehicles than for diesel vehicles. When assessing the impacts on a city perspective, results revealed that the impacts of cold start increase for more local streets. The main finding of this study is to provide evidence that a higher increase on emissions occurs on more local streets, where most of the population lives. This kind of knowledge is of particular relevance to urban planners in order to perform an informed definition of public policies and regulations to be implemented in the future, to achieve a cleaner and healthier urban environment.

2018-07-15Journal article

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Evaluation of technological solutions for compliance of environmental legislation in light-duty passenger: a numerical and experimental approach

Publication . Taborda, A. M.; Varella, R. A.; Farias, T. L.; Duarte, Gonçalo

This work includes an original approach that combines on-road experimental fuel use and emission maps and a numerical analysis to assess the impacts of fuel efficiency and NOx emission reduction technologies on a light-duty passenger vehicle. The solutions analyzed include Stop/Start, vehicle mass reduction up to 100 kg, drag coefficient reduction, as well as SCR and Lean NOx Trap systems. For this purpose, a reference EURO 6 diesel vehicle was monitored under real world driving conditions with a PEMS and the experimental data obtained allowed building engine maps of fuel use and NOx emission to be used on AVL Cruise software. The results obtained with Cruise were firstly validated with the experimental data (with errors up to 10,6% on fuel and 17,5% on NOx) and then the solutions implemented were tested individually and simulated on 48 real-world driving cycles. The results pointed to Stop/Start, mass reduction of 100 kg and SCR as the most effective solutions in reducing fuel consumption and NOx emission up to 14,6% and 57,5%, respectively, depending on driving context. The combination of these technologies was tested and the results showed maximum fuel savings of 17% on urban context and a maximum reduction of 58% on NOx on combined driving cycles. Despite all the efforts, real-world driving presents NOx emissions not yet compliant with standards, indicating the need for new strategies in order to face the environmental challenges.

2019-05Journal article

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How do road grade, road type and driving aggressiveness impact vehicle fuel consumption? Assessing potential fuel savings in Lisbon, Portugal

Publication . Faria, Marta; Duarte, Gonçalo; Varella, Roberto A.; Farias, Tiago; Baptista, Patricia

The transportation sector contributes significantly to energy consumption with inherent consequences in terms of emission of local pollutants, which is associated with air quality deterioration. Considering that driving behavior significantly influences fuel consumption, this work goal was to assess how driving aggressiveness is influenced by the type of road and by the road grade, and consequently their impacts on fuel consumption. For that purpose, 47 drivers were monitored in the Lisbon Metropolitan Area during 6 months, allowing building an extensive 1 Hz real world driving database (similar to 33,000 trips, totalizing 28.9 million seconds). This database provided distinctive and representative data, allowing assessing the impacts on fuel consumption rates. Results showed that both road context and aggressive driving behavior impact fuel consumption rates significantly. However, for non-aggressive driving behavior fuel consumption rates increased more with road grade increments (up to 3 times) than for aggressive driving behavior (up to 2.3 times). Furthermore, this study results demonstrated that aggressiveness influences fuel consumption differently across road grades. Aggressiveness impacts are higher for lower road grades, with increased fuel consumption rates by up to 255%. The key findings associated to this research work are that aggressiveness on roads with lower grades tends to correlate with higher percent increase on fuel consumption for all speed ranges. Moreover, aggressiveness seems to correlate with higher fuel consumption on urban streets. Consequently, a reduction in driving under these conditions can offer significant savings in fuel consumption.

2019-07Journal article

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Novel approach for connecting real driving emissions to the European vehicle laboratorial certification test procedure

Publication . Varella, Roberto A.; Ribau, João; Baptista, Patricia; Sousa, Luís; Duarte, Gonçalo

Vehicle emission certification is evaluated under laboratorial conditions, where vehicles perform a standard driving cycle in controlled conditions leading to several critics, which have resulted in the implementation of the Worldwide harmonized Light Vehicle Test Procedure (WLTP) and the Real Driving Emissions (RDE) testing procedure, as a complementary certification procedure. RDE is still under debate since boundary conditions; evaluation and trip selection methods are still being studied to allow test reproducibility. Currently, the official data analysis method uses the moving average window (MAW_EC), based on the WLTP CO2 emissions for trip validity evaluation (RDE package 4) and emissions (RDE package 3). However, this does not consider the impact of vehicle dynamics. Consequently, this work focuses on developing a novel method to relate certification driving cycle dynamics and on-road test vehicle dynamics, to evaluate RDE tests fuel use and exhaust emissions in a comparable way to certification driving cycles, indicating how close, or far, real-world driving is from the laboratorial certification test. For this, a new method was developed called road vehicle evaluation method (ROVET), which relies on the cycle vehicle dynamic and on-road trip dynamics for assessing if both tests are comparable. Results from 5 measured vehicles with a portable emissions measurement system (PEMS) through reproducibility tests and 2 case studies, show that the ROVET provides results closer to the certification calculated reference than the most commonly used method in Europe (1% avg. difference for ROVET while 8% avg. difference for MAW_EC, regarding CO2 emission, for example). The use of vehicle dynamics on construction and references of a method could be used to incentivize the regulators to review the references used by the current used methods, which suffers several criticisms since their release. As the regulated methods are in constant update, this study could be useful for helping to improve or to be used as additional method for future vehicle certification procedures.

2019-12Journal article

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