1,720,967 research outputs found
Experimental analysis of an early diesel PCCI concept and strategies to limit its application constraints
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Effect of Coolant Temperature on Performance and Emissions of a Compression Ignition Engine Running on Conventional Diesel and Hydrotreated Vegetable Oil (HVO)
Full text linkTo meet future goals of energy sustainability and carbon neutrality, disruptive changes to the current energy mix will be required, and it is expected that renewable fuels, such as hydrotreated vegetable oil (HVO), will play a significant role. To determine how these fuels can transition from pilot scale to the commercial marketplace, extensive research remains needed within the transportation sector. It is well-known that cold engine thermal states, which represent an inevitable portion of a vehicle journey, have significant drawbacks, such as increased incomplete combustion emissions and higher fuel consumption. In view of a more widespread HVO utilization, it is crucial to evaluate its performance under these conditions. In the literature, detailed studies upon these topics are rarely found, especially when HVO is dealt with. Consequently, the aim of this study is to investigate performance and exhaust pollutant emissions of a compression ignition engine running on either regular (petroleum-derived) diesel or HVO at different engine thermal states. This study shows the outcomes of warm-up/cool-down ramps (from cold starts), carried out on two engine operating points (low and high loads) without modifying the original baseline diesel-oriented calibration. Results of calibration parameter sweeps are also shown (on the same engine operating points), with the engine maintained at either high or low coolant temperature while combustion phasing, fuel injection pressure, and intake air flow rate are varied one-factor at a time, to highlight their individual effect on exhaust emissions and engine performance. HVO proved to produce less engine-out incomplete combustion species and soot under all examined conditions and to exhibit greater tolerance of calibration parameter changes compared to diesel, with benefits over conventional fuel intensifying at low coolant temperatures. This would potentially make room for engine recalibration to exploit higher exhaust gas recirculation, delayed injection timings, and/or lower fuel injection pressures to further optimize nitrogen oxides/thermal efficiency trade-off
Preliminary Optimization of the PCCI Combustion Mode in a Diesel Engine through a Design of Experiments
Full text linkAnalisi sperimentale di una combustione diesel non convenzionale - Ottimizzazione mediante l'applicazione di tecniche statistiche
No full textUna combustione ad elevato grado di premiscelazione è stata implementata in un motore diesel Euro VI, per diminuire contemporaneamente le emissioni di NOx e PM. Tecniche statistiche hanno permesso di ridurre il numero dei test mantenendo un elevato grado di predittvità dell'interazione dei parametri del motore su emissioni, consumi e rumore. Sono state ridotte le emissioni di NOx del 90% e di PM del 99%, a scapito di un aumento del consumo di combustibile e delle emissioni di HC e CO
Emissions, Performance and Vibro-Acoustic Analysis of a Compression-Ignition Engine Running on Hydrotreated Vegetable Oil (HVO)
No full textTo meet future energy sustainability and carbon neutrality requirements, disruptive changes to the current energy mix are expected. Renewable fuels, such as hydrotreated vegetable oil (HVO), could play an important role in this context. To assess the potential of HVO, further quantitative research analyses are still required in order to emphasize the benefits (and drawbacks, if any) from a global perspective, rather than limiting the investigation to a single topic (e.g., emissions).
For this purpose, HVO and conventional diesel were compared, in this study, running initially the engine with the same (diesel-oriented) calibration, before being optimized using purposely developed fuel-specific calibrations.
In terms of exhaust pollutant emissions, HVO showed the potential to substantially reduce engine-out emissions of soot, HC and CO at low loads, while differences in exhaust emissions at higher loads proved to be mainly determined by the amount of oxygen available in the combustion chamber, rather than the specific characteristics of the fuels. HVO also demonstrated reductions in tank-to-wheel CO2 emissions, due to lower fuel consumption, even though the primary benefit of renewable fuels should be highlighted in a larger well-to-wheel analysis.
In addition to emission analyses, since extensive investigations on the area of vibroacoustic behavior of engines running on renewable fuels are rare in the literature, a thorough comparison between regular diesel and HVO was carried out on this aspect. In this preliminary activity, the acoustic analysis focused solely on combustion noise, which was extracted by using dedicated signal processing techniques. This approach allowed the authors to focus on the noise contribution that is specifically influenced by the fuel characteristics. Furthermore, the vibrations of the engine block were evaluated. The results showed slightly lower levels of HVO in terms of both noise and vibrations
Emission reduction potential of hydrotreated vegetable oil (HVO) in a dual-loop EGR diesel engine with fuel-specific optimized calibration
No full textIn the pursuit of carbon neutrality, biofuels offer a viable alternative to reduce net CO2 emissions, as their production absorbs CO2. Hydrotreated vegetable oil (HVO), a second-generation biodiesel, offers several advantages with respect to fatty acid methyl esters (FAME). In particular, HVO can be also utilized pure without significant modifications to current diesel technology. This paper shows the potentialities of using pure HVO in a prototype dual-loop EGR diesel engine derived from a modern Euro 6 latest-generation version. Preliminary experimental tests show appreciable advantages when HVO is used as a drop-in fuel, that is, without any modification to the original diesel-oriented engine calibration. Substantial reductions in HC, CO and soot engine-out emissions are obtained, with variations in NOx primarily depending on the specific engine operating conditions. Nevertheless, the paper shows that even greater benefits can be achieved with dedicated HVO-specific calibrations, optimized using statistical techniques of Design of Experiments (DoE). For instance, a tailored HVO-specific calibration that maximizes NOx reductions could decrease NOx engine-out emissions by approximately 30% at medium-to-high load and as much as 60% at low load, if compared to a diesel-oriented calibration targeting the same objectives. The study also compares other engine-out emissions and noise levels by implementing alternative dedicated calibrations aimed at minimizing CO or brake specific fuel consumption, depending on the operating point considered
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Comparison of the Emissions, Noise, and Fuel Consumption Comparison of Direct and Indirect Piezoelectric and Solenoid Injectors in a Low-Compression-Ratio Diesel Engine
Full text linkAn experimental investigation has been carried out to compare the performance and
emissions of a low-compression-ratio Euro 5 diesel engine featuring high EGR rates, equipped
with dierent injector technologies, i.e., solenoid, indirect-acting, and direct-acting piezoelectric.
The comparisons, performed with reference to a state-of-the-art double fuel injection calibration,
i.e., pilot-Main (pM), are presented in terms of engine-out exhaust emissions, combustion noise
(CN), and fuel consumption, at low–medium engine speeds and loads. The dierences in engine
performance and emissions of the solenoidal, indirect-acting, and direct-acting piezoelectric injector
setups have been found on the basis of experimental results to mainly depend on the specific features
of their hydraulic circuits rather than on the considered injector driving system
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