348 research outputs found
Comparative Evaluation of Data-Driven Approaches to Develop an Engine Surrogate Model for NOx Engine-Out Emissions under Steady-State and Transient Conditions
No full textIn this paper, a methodology based on data-driven models is developed to predict the NOx emissions of an internal combustion engine using, as inputs, a set of ECU channels representing the main engine actuations. Several regressors derived from the machine learning and deep learning algorithms are tested and compared in terms of prediction accuracy and computational efficiency to assess the most suitable for the aim of this work. Six Real Driving Emission (RDE) cycles performed at the roll bench were used for the model training, while another two RDE cycles and a steady-state map of NOx emissions were used to test the model under dynamic and stationary conditions, respectively. The models considered include Polynomial Regressor (PR), Support Vector Regressor (SVR), Random Forest Regressor (RF), Light Gradient Boosting Regressor (LightGBR) and Feed-Forward Neural Network (ANN). Ensemble methods such as Random Forest and LightGBR proved to have similar performances in terms of prediction accuracy, with LightGBR requiring a much lower training time. Afterwards, LightGBR predictions are compared with experimental NOx measurements in steady-state conditions and during two RDE cycles. Coefficient of determination (R2), normalized root mean squared error (nRMSE) and mean average percentage error (MAPE) are the main metrics used. The NOx emissions predicted by the LightGBR show good coherence with the experimental test set, both with the steady-state NOx map (R2 = 0.91 and MAPE = 6.42%) and with the RDE cycles (R2 = 0.95 and nRMSE = 0.04)
How SES May Affect Reading Comprehension and Vocabulary in Language Minority Bilingual and Monolingual Children
No full textWe investigated the role of socioeconomic status (SES) in the unfolding of vocabulary and text-comprehension skills in language minority bilingual children, who are educated exclusively in their L2. For comparison, a monolingual control group was also tested, consisting of children of the same age and schooling. We administered a synonyms task to measure vocabulary and an inference test to measure reading comprehension. Socioeconomic status scores were obtained through the Hollingshead Four Factor Index questionnaire. Our results showed that being bilingual did not influence vocabulary and text-comprehension skills in the age group being tested (9-11 years). Whereas, SES played a significant role in relation to age and schooling. Interestingly, two different mediation analyses demonstrated that vocabulary knowledge accounted for a significant portion of the causal relationship between SES and reading comprehension, and that reading comprehension itself can explain part of the relationship between SES and vocabulary. The social and educational implications of the findings are discussed
Knock (and pre-ignition) damage on engine components: Case studies
No full textDue to the stringent regulations in terms of CO2 emissions, in order to increase engine efficiency, design strategies are oriented towards both increased spark advance and higher compression ratio, determining a higher probability to induce knock and abnormal combustions. Since slight knock does not lead to compromising engine damage, it should be tolerated in order to pursue the maximum efficiency. In the present study, knocking damages on several combustion chamber components after industrial durability tests are shown, aiming to underline the main effects of knock and to guide materials and coatings selection. Some hints are also made to the deleterious effects caused by persistent knocking combustions turning into pre-ignition. Piston Al alloys are usually more sensitive to knock induced thermo-mechanical stresses, but also cylinder heads, liners and spark plugs might be affected
Knock (and pre-ignition) damage on engine components: case studies
No full textPer ridurre il problema del riscaldamento globale, gli enti normatori impongono ai costruttori limiti sempre più stringenti su emissioni CO2 e consumi dei veicoli, spingendo la ricerca verso la massimizzazione dell’efficienza. È noto come l’efficienza cui può operare un motore ad accensione comandata (rapporti di compressione, anticipo) sia limitata dalla detonazione che, per via dei problemi di affidabilità ad essa associati, in passato veniva evitata a spese dei consumi, mentre ora deve essere tollerata e controllata. In generale è il pistone, tipicamente in lega di Al, a risentire maggiormente del danno da detonazione, che si presenta come erosione superficiale nei casi più lievi, ma può arrivare ad incollaggio del segmento, formazione di canali di blow-by e grippaggio nel caso in cui degeneri in preaccensione. Ulteriori danni si possono riscontrare su canne cilindro, teste motore, candele. L’articolo raccoglie case studies su motori sovralimentati e aspirati, allo scopo di orientare la scelta dei materiali sulla base delle criticità evidenziate
Knock induced erosion on Al pistons: Examination of damage morphology and its causes
No full textIn the present study, a systematic and deep examination of knocking damage on Al pistons is carried out, highlighting that only when exceeding a certain threshold knock compromises engine functionality. Controlled knocking combustions were induced during bench tests, by varying the spark advance for each cylinder. Several knock intensities and frequencies were investigated, with the aim to evaluate the possible knocking damages and to understand their influence on piston functionality. All the observed damages have been separately described and studied through failure analysis techniques, in particular optical and scanning electron microscopy and 3D digital microscopy, providing explanations of their occurrence. Among them, the erosion damage was predominantly observed and therefore fully evaluated. Preliminary attempts to relate engine parameters to knock damage were also made. This study is part of a wider project, whose aim is to increase knocking limits from the “safe calibration area” up to the limits which produce acceptable damages on pistons, in order to enhance engine efficiency
Estudo preliminar de análises de parâmetros genéticos em dados simulados de escores visuais com diferentes distribuições, por meio de inferência bayesiana. I.
No full textO objetivo neste estudo foi avaliar o efeito de diferentes distribuições de freqüência de dados e a utilização de modelo linear sobre os valores genéticos aditivos na avaliação de características categóricas. Foram simulados rebanhos com 40 touros e 1.200 fêmeas (1.000 vacas e 200 novilhas), acasalados aleatoriamente, acompanhados por 20 anos, e gerados efeitos aditivos direto e materno e de ambiente permanente materno. Para os produtos, foram geradas informações de grupos de manejo e o efeito da idade da vaca ao parto, os quais juntamente com os demais efeitos e um erro aleatório independente foram combinados para formar o valor fenotípico do animal na escala subjacente. Os dados na escala observada (escores visuais) foram gerados de forma a se obterem: distribuição normal relativa, distribuição normal fixa e distribuição normal relativa assimétrica. Foram geradas cinco repetições de cada distribuição, os componentes de (co)variância e os valores genéticos foram estimados por inferência bayesiana e foi obtida a correlação de Spearman entre os valores genéticos estimados e os valores genéticos verdadeiros dentro de cada categoria animal (touro, vaca e produto), para cada repetição e distribuição. Os valores de herdabilidade direta e materna estimados foram semelhantes para todas as distribuições, variando, quanto à repetição, de 0,19 a 0,26 e 0,07 a 0,12, respectivamente. As médias, das cinco repetições, das correlações de Spearman dos valores genéticos aditivos direto e materno verdadeiros com os estimados foram de 0,85 e 0,56 (touros), 0,52 e 0,45 (vacas) e 0,55 e 0,33 (produtos), respectivamente, em todas as distribuições. A distribuição relativa assimétrica se mostrou levemente inferior às outras duas formas de distribuições analisadas
An Enhanced Light Gradient Boosting Regressor for Virtual Sensing of CO, HC and NOx
No full textThe present study introduces a novel methodology that utilizes Light Gradient Boosting Regressors to predict engine-out emissions of NOx, HC, and CO. The accuracy of the proposed models is evaluated on different types of homologation cycles. The dataset used in this study is derived from a set of 47 experimental driving cycles, including RDE, WLTC, NEDC, ECE, US06, and HWFET. The experimental driving cycles are performed on a roll bench using a spark-ignited, naturally aspirated, V12 engine-equipped vehicle. A three-second sliding window is incorporated in the models to capture the dynamic behavior of pollutant emissions. The performance of the LightGBR models is assessed using the mean absolute percentage error (MAPE) on the total pollutant mass, which is found to be 5.2% for CO, 5.7% for HC, and 6.8% for NOx. The results demonstrate the efficacy of the proposed methodology, which can be used to estimate the impact of powertrain calibration changes on pollutant emissions in a virtual environment, thereby reducing the number and the cost of the experimental tests
CaRo 2.0: A system for social active listening and expressive performing of music content
No full textThe overwhelming influence of ptarmigan abundance on gyrfalcon reproductive success in the central Yukon, Canada
No full textCompanion studies of Willow Ptarmigan (Lagopus lagopus) and Gyrfalcons (Falco rusticolus) in the central Yukon from 1978 to 1983 allowed us to examine Gyrfalcon reproductive performance at 14 nest sites in relation to ptarmigan abundance and other potential effects, including weather variables, the previous year’s success, nest site characteristics, and Golden Eagle (Aquila chrysaetos) nesting density. Ptarmigan abundance declined six-fold and was mirrored by a significant decline in Gyrfalcon breeding success (breeding failure 58%, clutch desertion 33%). Clutch size showed little variation, although deserted nests held fewer eggs than did successful nests, and there were more four-egg clutches when ptarmigan were most abundant. An average of 2.26 young fledged per nest during abundant ptarmigan years, and 0.l8 when ptarmigan were declining. No other factors were correlated with Gyrfalcon reproductive success. Juvenile ptarmigan density had a compensatory effect: even when ptarmigan breeding numbers dipped, Gyrfalcons bred successfully if the proportion of juvenile ptarmigan was high. Clutch initiation date was a good predictor of Gyrfalcon breeding performance. Early clutches had more eggs (67% with 4 eggs compared to 27% in late nests), were less likely to be deserted (5% vs. 59%), and fledged more young (93% vs. 38%). Two Gyrfalcon pairs, supplemented with food in a poor ptarmigan year, fledged young at a rate and schedule comparable to pairs during a peak ptarmigan year. We discuss interesting observations about Gyrfalcon brood success, as well as Golden Eagle nesting density as a potentially important aspect of the reproductive ecology of Gyrfalcons in this population.Peer reviewedAuthor's reprint from Gyrfalcons and ptarmigan in a changing world
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