Academic literature on the topic 'Variabili di Shape'
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Journal articles on the topic "Variabili di Shape"
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Setiono, Danang, Parjanto Parjanto, and Djati Waluyo Djoar. "Identifikasi Morfologi Aksesi Srikaya (Annona squamosa) di Gedangsari Gunungkidul." Agrosains: Jurnal Penelitian Agronomi 15, no. 2 (2013): 32. http://dx.doi.org/10.20961/agsjpa.v15i2.18994.
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<p>The purpose of this study to determine the morphological characteristics and variability of planting sugar apple Gedangsari, Gunungkidul, Yogyakarta. Identify the morphological characteristics conducted on 36 plant samples (36 accessions) based method on stratified sampling and purposive sampling. The data were analyzed descriptively and clustering analysis. The results of the research showed that sugar-apple had pyramida canopy shape, plant height of 264±525 cm, oblongus leaves type, integer leaves margins, acuminatus leaves tip form, base acutus leaves, petiole cylindrical shape, dark green petiole, dark green color of the upper surface leaves, faded green color of the lower surface, leaves length 16.06±8.23 cm, leaves width 3,73±6,9 cm, leaves area 24,28±85,71 cm2, round shaped of rod, patens branching pattern, stem circumference 17,5±38 cm, axillary flos of flower layout, having 3 petals, whitish green of flower color, is cordate and round shape of fruit, fruit weight of 83,03±180,3 g, fruit circumference 22,4±19,36 cm, flesh thick 1,73±3,66 mm, whitish green and green of fruit color, the total amount of fruit scales 70±104,66, and the value of PTT between 18-29 obrix, blunt shape of fruit scales, ellipsoid shape of seeds, number seeds 7±70,66 and total seed weight 2,3±19,86g. There were variability include leaves length, leaves width, leaves area, stem girth, fruit weight, fruit girth, fruit flesh thickness, number of fruit scales, PTT values and fruit shape and the fruit skin’s color. The result of clustering analysis showed that similarity coefficient between the accessions was 66%.</p>
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Fornari, Edoardo, and Sebastiano Grandi. "Le promozioni di prezzo sulle marche private: variabilitÀ tra categorie ed effetti competitivi inter-brand." MERCATI & COMPETITIVITÀ, no. 4 (December 2011): 125–45. http://dx.doi.org/10.3280/mc2011-004009.
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Il presente lavoro discute il tema delle politiche di pricing di breve periodo praticate dai retailers sui prodotti di marca commerciale. In particolare l'analisi si focalizza sull'elaborazione dei dati di sell-out 2008-2009 relativi alle categorie merceologiche di Largo Consumo Confezionato (LCC) nell'ambito del mercato italiano della Distribuzione Moderna (ipermercati e supermercati). In tale contesto emerge un crescente ricorso alla promozione di prezzo per le linee di private label, soprattutto all'aumentare del valore complessivo del giro d'affari di categoria, della pressione promozionale sulle marche industriali e dell'entitÀ media dello sconto. Il lavoro evidenzia altresě come l'efficacia delle promozioni sulla marca commerciale possa risultare estremamente elevata in termini di generazione di vendite incrementali, di aumento della market share e di contributo alle vendite complessive.
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Sari, Ayu Nirmala, Evistiani Gulo, Arsiska F. Situmorang, and Jamaluddin Jamaluddin. "PENGARUH EARNING PER SHARE, RETURN ON EQUITY DAN NET PROFIT MARGIN TERHADAP HARGA SAHAM PADA PERUSAHAAN BATU BARA YANG TERDAFTAR DI BEI PERIODE 2015-2019." SCIENTIFIC JOURNAL OF REFLECTION : Economic, Accounting, Management and Business 4, no. 3 (2021): 458–64. http://dx.doi.org/10.37481/sjr.v4i3.324.
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Observation of the research results has a specific purpose to test any effect of the variabels Earning Per Share, Return On Equity, and Net Profit Margin on the share price of Coal Companies on the IDX for the 2015-2019 period. The population for this study used purposive sampling by using two analytical techniques used, namely multiple linear analysis and hypothesis testing using SPSS (Statistical Product and Service Solutions). Results The contribution of the three variabels is 25.5% and 74.5% is influenced by other factors. So based on the results of research tests there is a conclusion that the results of the Earning Per Share, Return On Equity variabel have no significant effect on stock prices, and Net Profit Margin has a significant effect on stock prices. Then the results of the three variabels Earning Per Share, Return On Equity, Net Profit Margin have an effect on the domain or simultaneously on stock prices.
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Liberatore, Giovanni, Tommaso Ridi, and Filippo Di Pietro. "Rilevanza ed affidabilità del valore contabile dell'avviamento e dei beni immateriali sul mercato italiano." FINANCIAL REPORTING, no. 3 (November 2012): 31–50. http://dx.doi.org/10.3280/fr2012-003003.
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Il presente lavoro si propone di indagare quale sia la rilevanza e l'affidabilità percepita dal mercato finanziario sul valore espresso nel bilancio d'esercizio sui beni immateriali e l'avviamento delle società quotate. Lo studio ha analizzato le aziende quotate al FTSE Italia All-share, nel periodo fra il 2002 ed il 2008. Attraverso un modello di regressione a più variabili si è verificato che: a) il valore contabile dei beni immateriali e dell'avviamento sono correlati positivamente al valore di mercato del capitale, b) la transizione agli IAS/IFRS non ha comportato un incremento della rilevanza ed affidabilità percepita dal mercato dei beni immateriali e avviamento.
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Septiadi, Dudi, and Muhammad Nursan. "SALURAN DAN EFISIENSI PEMASARAN TEMBAKAU VIRGINIA DI KABUPATEN LOMBOK TENGAH." AGROTEKSOS 34, no. 1 (2024): 338. http://dx.doi.org/10.29303/agroteksos.v34i1.1118.
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The issue of price variability has become an interesting debate in the Virginia tobacco economic chain. The existence of marketing institutions in the Virginia tobacco economic chain, on the one hand, provides price certainty for farmers, on the other hand, if the marketing chain is longer, the distribution of profits obtained by farmers will be smaller. This research aims to analyze marketing channels and marketing efficiency of Virginia tobacco farming in Central Lombok Regency. The method used in this research is the descriptive method. Virginia tobacco marketing channel analysis uses a descriptive analysis approach, while Virginia tobacco marketing efficiency uses marketing margin, farmer's share and profit distribution analysis. The results of the research show that there are 2 types of marketing channels for Virginia tobacco in Central Lombok Regency, namely Marketing Channel I: Farmers - Collectors - Wholesalers; and Marketing Channel II: Farmers – Wholesalers. Marketing channels I and II of Virginia tobacco in Central Lombok Regency are declared to be efficient because the farmer's share value is 95% with a margin of IDR 2,333 and the profit distribution value is 1 in marketing channel I; and the farmer's share value is 100% in marketing channel II.. Keywords : Channels, Marketing, Tobacco, Virginia.
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Shi, Peijian, Ülo Niinemets, Cang Hui, Karl J. Niklas, Xiaojing Yu, and Dirk Hölscher. "Leaf Bilateral Symmetry and the Scaling of the Perimeter vs. the Surface Area in 15 Vine Species." Forests 11, no. 2 (2020): 246. http://dx.doi.org/10.3390/f11020246.
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The leaves of vines exhibit a high degree of variability in shape, from simple oval to highly dissected palmatifid leaves. However, little is known about the extent of leaf bilateral symmetry in vines, how leaf perimeter scales with leaf surface area, and how this relationship depends on leaf shape. We studied 15 species of vines and calculated (i) the areal ratio (AR) of both sides of the lamina per leaf, (ii) the standardized symmetry index (SI) to estimate the deviation from leaf bilateral symmetry, and (iii) the dissection index (DI) to measure leaf-shape complexity. In addition, we examined whether there is a scaling relationship between leaf perimeter and area for each species. A total of 14 out of 15 species had no significant differences in average ln(AR), and mean ln(AR) approximated zero, indicating that the areas of the two lamina sides tended to be equal. Nevertheless, SI values among the 15 species had significant differences. A statistically strong scaling relationship between leaf perimeter and area was observed for each species, and the scaling exponents of 12 out of 15 species fell in the range of 0.49−0.55. These data show that vines tend to generate a similar number of left- and right-skewed leaves, which might contribute to optimizing light interception. Weaker scaling relationships between leaf perimeter and area were associated with a greater DI and a greater variation in DI. Thus, DI provides a useful measure of the degree of the complexity of leaf outline.
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Hakiki, Moh Saiful, Riyan Sisiawan Putra, Andi Harmoko Arifin, Julia Safitri, and Martino Wibowo. "PENINGKATAN PENGARUH KINERJA KEUANGAN TERHADAP DINAMIKA HARGA SAHAM DENGAN PROFITABILITAS SEBAGAI VARIABEL MODERASI PADA BANK UMUM DI INDONESIA." Media Mahardhika 22, no. 3 (2024): 377–87. http://dx.doi.org/10.29062/mahardika.v22i3.922.
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This research aims to analyze the relationship between commercial bank financial performance, share price dynamics, and the role of profitability as a moderating variable. Data from 47 commercial banks (conventional and sharia) in Indonesia during the period from the first quarter of 2021 to the third quarter of 2023 was used to test the hypothesis. Independent variables include Net Interest Margin (NIM) and Operational Costs compared to Operating Income (BOPO), while the dependent variable is share price dynamics. Profitability, measured through Return On Assets (ROA) and Return On Equity (ROE), is implemented as a moderating variable. The results of the moderated multiple regression analysis show that financial performance does not directly have a significant influence on stock prices. On the other hand, profitability directly has a positive effect on stock prices. Furthermore, profitability strengthens the relationship between financial performance and share prices, indicating that banks with high profitability tend to experience a more significant impact of financial performance on share price changes. Although it only explains 13.4% of share price variability, these findings provide an in-depth understanding of the factors influencing share price dynamics in the banking sector.
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Ernawati, Nani, Yulianita Rahayu, Yoyok Prasetyo, Darwin Nahwan, and Edi Kurniawan. "PROFITABILITAS DAN PENGARUHNYA PADA HARGA SAHAM SEKTOR PERBANKAN." Ekono Insentif 16, no. 2 (2022): 82–91. http://dx.doi.org/10.36787/jei.v16i2.885.
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Abstrak
 Secara konseptual, kinerja perusahaan akan berdampak terhadap variabilitas harga saham. Namun terdapat beberapa data empiris khususnya di sektor perbankan mengindikasikan hal yang berbeda. Pada studi awal yang dianalisa secara grafis menunjukan trend profitabilitas tidak seluruhnya menunjukan hubungan yang relevan terhadap variabilitas harga saham. Di samping itu, hasil penelitian terkait topik tersebut pun menunjukan hasil yang berbeda-beda. Dengan demikian penelitian ini bertujuan untuk menguji secara statistik pengaruh rasio profitabilitas terhadap harga saham dengan studi kasus data rasio profitabilitas dan harga saham perusahaan perbankan yang terdaftar di Bursa Efek Indonesia selama periode 5 tahun. Penelitian ini menggunakan pendekatan kuatitatif, di mana sampel diambil secara purposive dan dihasilkan delapan belas sampel perusahaan. Dengan menggunakan teknik regresi data panel diperoleh hasil analisa verifikatif di mana secara simultan rasio profitabilitas berbengaruh terhadap harga saham, sedangkan secara parsial rasio profitabilitas yang diproksikan dengan Return on Asset (ROA) dan Earning per Share yang berpengaruh terhadap harga saham, sedangkan Net Profit Margin (NPM) tidak mempengaruhi variabilitas harga saham.
 
 Abstract 
 Conceptually, the company's performance will greatly affect the variability of stock prices. However, in practice there are some empirical data, especially in the banking sector, which indicate different things. Preliminary studies which were analyzed graphically showed that the trend of profitability did not fully affect the variability of stock prices significantly. In addition, several research gaps were found on the same problem. Based on this matter, the purpose of this study is to statistically examine the effect of profitability ratios on stock prices with a case study of profitability ratio data and stock prices of banking companies listed on the Indonesia Stock Exchange within 5 years of period. This study uses a quantitative approach, eighteen purposive samples were taken. By using panel data regression technique, the results of verification analysis show that simultaneously, profitability ratios affect stock prices, and partially, profitability ratios proxied by Return on Assets (ROA) and Earnings per Share also affect stock prices, while Net Profit Margin (NPM) does not affect stock price variability.
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Puspita*, Gadis Arimbi, and Irni Yunita. "Market Reaction and Share Performance Towards the Merger and Acquisition Announcement of 2015-2019." Jurnal Ilmu Keuangan dan Perbankan (JIKA) 12, no. 1 (2022): 51–61. http://dx.doi.org/10.34010/jika.v12i1.7231.
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This study aims to analyze differences in market reactions and performance before and before announcing Mergers and Acquisitions in companies listed on the Indonesia Stock Exchange (IDX) in 2015-2019 by measuring differences in Abnormal Return (AR), Trading Volume Activity (TVA), Security Return Variability (SRV), and Actual Return (R) 10 days before and 10 days after the event. The method used is quantitative. The data used are secondary data on daily closing stock prices and the number of shares held during the observation period. The test results show that there is no significant difference in Abnormal Return (AR), Trading Volume Activity (TVA), and Actual Return (R) before and before the event. However, there is a significant difference in the Security Return Variability (SRV) before and before the event. 
 Keywords: Abnormal Return; Trading Volume Activity; Security Return Variability; Actual Return; Merger and Acquisition
 
 Penelitian ini bertujuan untuk menganalisis perbedaan reaksi pasar dan kinerja saham Before dan After pengumuman merger dan akuisisi pada perusahaan terdaftar di Bursa Efek Indonesia (BEI) tahun 2015-2019 dengan mengukur perbedaan Abnormal Return (AR), Trading Volume Activity (TVA), Security Return Variability (SRV), dan Actual Return (R) 10 hari Before dan 10 hari setelah peristiwa. Metode yang digunakan adalah kuantitatif. Data yang digunakan adalah data sekunder harga saham penutupan harian dan jumlah saham yang diperdagangkan selama periode pengamatan. Hasil uji menunjukkan tidak ada perbedaan signifikan pada Abnormal Return (AR), Trading Volume Activity (TVA) dan Actual Return (R) Before dan After peristiwa. Namun terdapat perbedaan yang signifikan pada Security Return Variability (SRV) Before dan After peristiwa.
 Kata Kunci: Return Tidak Normal; Aktivitas Volume Perdagangan; Variabilitas Pengembalian Keamanan; Return Aktual; Penggabungan dan Akuisisi
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Kamilah, Aisyatul, Siti Kholidatur Rodiyah, and Nailul Ulah Al Chumairoh. "Pengaruh Penanaman Nilai Budaya Religius dan Lingkungan Sekolah Terhadap Pembentukan Karakter Siswa di SMP Hamalatul Quran Ringinagung Kediri." YASIN 5, no. 3 (2025): 2202–11. https://doi.org/10.58578/yasin.v5i3.5637.
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Rapid technological changes have both pros and cons, especially for children. Education that emphasizes positive and negative values is crucial for character development in a global society. Through religious education, the ideals of divinity and humanism in Islam shape students' character. This study examines how Islamic cultural values and the educational environment shape student character at SMP Hamalatul Quran Ringinagung Kediri. Data were obtained through surveys, observations, and documentation. Most questionnaire scores fell within the upper range, peaking at 115-116. Validity and reliability tests verified the research instrument. Data were normally distributed, and the regression type was free from multicollinearity and heteroskedasticity. Multiple linear regression analysis revealed that religious cultural values (X1) did not have a significant impact on student character (Y), whereas the school environment had a positive and substantial effect on character education (Y). The coefficient of determination (R²) of 0.295 indicates that religious cultural values and the school environment explain 30% of the variability in student character, although other variables also play a role. The F test revealed that both independent factors significantly affect the dependent variable. This study shows that religious cultural values and the educational environment significantly influence student character. Promoting religious principles in the curriculum, school activities, and a supportive atmosphere can help students develop integrity and morality.
Dissertations / Theses on the topic "Variabili di Shape"
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LIMATOLA, GIOVANNI. "Infrared Linear Renormalons in Collider Processes." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2023. https://hdl.handle.net/10281/402371.
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Al fine di descrivere appropriatamente le osservabili studiate tramite collisori
adronici e/o leptonici, risulta cruciale una corretta comprensione delle
correzioni non perturbative (che si manifestano come correzioni di potenza),
lineari nel rapporto tra una scala di energia non perturbativa e la
scala caratteristica del processo. Utilizzando un modello abeliano ricerchiamo
tali effetti nella distribuzione in momento trasverso di un bosone Z prodotto
con un jet in collisioni adroniche, essendo questa una delle osservabili meglio
misurate presso LHC. La presenza delle correzioni non perturbative di cui sopra
impedirebbe di raggiungere la precisione sperimentale, anche considerando
ordini superiori nello sviluppo perturbativo. Non avendo individuato alcuna
correzione di questo tipo tramite tecniche semi numeriche, abbiamo scelto di adottare
un approccio più rigoroso dal punto di vista teorico, fornendo una spiegazione
attorno al manifestarsi di tali correzioni di potenza.
Tale comprensione teorica è stata applicata allo studio delle variabili di shape
in annichilazione $e^+e^-$, con particolare attenzione allo studio del
C-parametro e del thrust, e ottenendo per tali osservabili una stima delle
correzioni non perturbative nella regione dei tre jet per la prima volta.
In tale lavoro è stata altresì ottenuta un'espressione fattorizzata per le
correzioni non perturbative per alcune osservabili, con un termine dipendente
dalla variazione dell'osservabile a seguito dell'emissione di un partone
soffice, e un termine costante e universale, proporzionale al cosiddetto
Milan factor.
Tali osservabili sono ampiamente utilizzate al fine di estrarre valori della
costante di interazione forte $\alpha_s$ e costituiscono il contesto ideale al fine
di compiere studi di QCD perturbativa.
È dunque estremamente importante ottenere stime affidabili delle correzioni
non perturbative nell'intera regione di spazio delle fasi rilevante per i fit
di $\alpha_s$.<br>Understanding leading non-perturbative corrections, showing up as linear power corrections,
is crucial to properly describe observables both at lepton and hadron colliders.
Using an abelian model, we examine these effects for the transverse momentum distribution
of a $Z$ boson produced in association with a jet in hadronic collisions, that is one of the
cleanest LHC observables, where the presence of leading non-perturbative corrections would spoil
the chance to reach the current experimental accuracy, even considering higher orders in the perturbative expansion.
As we did not find any such corrections exploiting semi-numerical techniques, we looked for
a rigorous field-theoretical derivation of them, and explain under which circumstances linear power corrections can arise.
We apply our theoretical understanding to the study of event-shape
observables in $e^+e^-$ annihilation, focusing in particular on $C$-parameter and thrust,
and obtaining for them an estimate of non-perturbative corrections in the three-jet region for the first time.
We also derived a factorisation formula for non-perturbative corrections, with a term describing
the change of the shape variable when a soft parton is emitted, and a constant universal factor,
proportional to the so-called Milan factor.
These observables are routinely used to extract the strong coupling constant $\alpha_s$ and
they constitute an environment to test perturbative QCD.
It is then extremely important to obtain reliable estimates of non-perturbative corrections in the whole kinematic region relevant for the $\alpha_s$ fits.
Conference papers on the topic "Variabili di Shape"
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Rathnaraj, J. David, B. Jefferson Raja Bose, and Michael N. Kumar. "Simulation and Experimental Investigation of Variable Swirl Intake Port in DI Diesel Engine Using CFD." In ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98066.
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Knowledge of the flow phenomena inside the cylinder is necessary for optimum design of the intake port and the piston cavity configurations. Recent trends in direct injection diesel engines have increased the need for clear understanding of the flow field, especially the swirl characteristics. The swirl flow is an essential parameter which affects the air fuel mixing, combustion efficiency and therefore the engine performance. The purpose of this study is to investigate the combustion, emission, spray and flow field phenomena of a D I diesel engine and to come up with a geometrical shape for a port and valve or valves that produce the optimum swirl ratio. The percentage opening of a helical port for the DI diesel engine is simulated and studied using Computational Fluid Dynamics with experimental validation. Steady flow rig experiments are most widely used to evaluate the swirl ratio of an intake port design. The three dimensional developing flow patterns are needed throughout the compression and combustion stroke to understand the various experimental results. Flow is simulated by solving governing equations, viz., conservation of mass and momentum using the simple-algorithm. Turbulence has been modeled by standard kφ–φ∈ model with standard wall treatment. The predictive accuracy of the calculation method is compared with detailed mass flow rate and paddle rpm measurements. The results are in good agreement with experimental results and clearly predict the under predictability of the paddle swirl meter in lower lifts. Emission standards, which demand large reduction in NOx and PM emission, require a more comprehensive study of all elements that contribute to emission formulation. The combustion chamber is subject of research and development in an effort to achieve optimized combustion system. The intake port fluid dynamics contribute to the fuel air mixing which in turn is the most important parameter for the control of fuel burning rate for diesel engines. The intake port fluid dynamics also significantly affects ignition delay, the magnitude and timing of the diffusion burn, the magnitude of the premixed burn and emission of nitrous oxide and soot. According to the Modulated Kinetics (MK) concept, which improves the emission performance of diesel engines, a D I Diesel engine requires higher intake swirl in the part-load region. The computations are used to optimize the swirl flow characteristics of an intake port system over a wide range of operating conditions. In this study, the numerical simulation of the helical intake port and variable swirl intake port for two-valve DI Diesel engines are discussed with experimental validation. The improvement of swirl generation capacity of the port design according to the stringent emission norms are also studied.
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Boretti, Alberto. "Improving Efficiency and Power Density of Hydrogen Engines of Positive Ignition Single-Fuel and Compression Ignition Dual-Fuel designs." In FISITA World Congress 2021. FISITA, 2021. http://dx.doi.org/10.46720/f2020-caf-001.
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The latest advances in power density and efficiency of internal combustion engines (ICEs), both diesel direct injection (DI) compression ignition (CI), and gasoline positive ignition (PI), DI and jet ignition (JI), ICEs, are transferrable to single fuel or dual fuel hydrogen engines (H2-ICEs). H2-ICEs have the potential to deliver peak efficiency about 50%, peak power efficiency above 46%, and cycle average efficiency above 35% when fitted to hybrid powertrains. The major hurdles to achieve these performances are the development of hydrogen injection system. Dual fuel DI diesel-hydrogen CI ICEs have the potentials to deliver extremely low emissions of the regulated pollutants, NOx, unburned hydrocarbons (HC), CO and particulate matter (PM), and CO2 emission. Hydrogen PI ICEs with DI and JI have the potentials to deliver extremely low emissions of the regulated pollutant NOx, practically zero emissions of regulated pollutant PM, and practically zero emission of CO2 (while a small amount of lubricating oil may end up in the combustion chamber, but this amount is negligible). The PI ICEs allow much higher power densities, being the combustion event controlled by the turbulent mixing rather than vaporization, mixing and diffusion times. Thus, combustion duration is about independent of the engine speed in PI ICEs but increasing with the engine speed in CI ICEs. While combustion of hydrogen only in a CI engine is still troublesome, needing added research and development, much simpler is the use of hydrogen and diesel in a dual fuel CI engine accepting the DI of both diesel and hydrogen. While the dual-fuel DI diesel-hydrogen CI ICEs are a workable short-term replacement of the traditional hydrocarbon fueled PI ICEs, as cryogenic H2-ICES may share infrastructure and fuel system technology with LNG-ICEs, the hydrogen PI ICEs with DI and JI are an even better environmentally-friendly proposal while offering better performances. Simulations are presented for a dual duel diesel-hydrogen engine featuring two injectors per cylinder, one for the diesel and one for the hydrogen. The coupling of a pilot/pre-injection of diesel with a main injector of hydrogen is straightforward. Mixed modes of combustion are possible injecting part of the hydrogen before, and a part after the diesel injection ignition. The engine has a super turbocharging, where the turbocharger shaft is connected to the crankshaft by gears and a continuously variable transmission. Steady-state maps are presented in detail. Even if this aspect is not investigated, thanks to the super turbocharging, the engine has excellent transient behaviors, in decelerations (energy recovery) as well as accelerations (no turbo-lag). Dual fuel CI ICEs have also the advantage of a hydrogen city driving delivering extremely low emissions of pollutants as well as CO2, and a diesel interstate and rural areas driving delivering still relatively low emissions of pollutants as well as CO2.
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Baratta, Mirko, Andrea E. Catania, and Francesco C. Pesce. "Computational and Experimental Analysis of Direct CNG Injection and Mixture Formation in a Spark Ignition Research Engine." In ASME 2010 Internal Combustion Engine Division Fall Technical Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/icef2010-35103.
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Direct injection (DI) of compressed natural gas (CNG) under high pressure conditions is a topic of great interest, owing to its potential for improving SI engine performance and fuel consumption. However, relevant technical difficulties have yet to be resolved in order to stabilize combustion process, especially for stratified engine operating conditions. The present paper is focused on experimental and numerical investigations of the jet formation and fuel-air mixing process in a research optical-access single-cylinder engine. The engine is based on the multi-cylinder engine under development within the European Community (EC) VII Framework Program (FP) InGAS Integrated Project, and features a centrally mounted poppet-valve injector on a pent-roof combustion chamber with a bowl in piston. Experimental investigations were made by means of the planar laser-induced fluorescence technique, and revealed a cycle-to-cycle jet shape variability. In particular, for specific cylinder pressure values at the start of injection, the jet can adhere to chamber walls for a relevant number of cycles, leading to an ‘umbrella-like’ shape. This can change the mixing capabilities of the combustion chamber and cause instabilities in the combustion process. The mentioned behaviour is strongly dependent not only on the injection and cylinder pressures, but also on important design parameters, such as needle cone angle and in-chamber injector protrusion. For this reason, in order to obtain a deep insight into the injected gas behaviour on an average cycle basis, the experimental investigation was supported by a numerical analysis. Simulations were carried out by an optimized variable-density finite-volume numerical model which was built within the Star-CD environment. A previously developed and validated ‘virtual injector’ model was implemented. The outcomes of the numerical model were compared to laser-induced fluorescence images, for both stratified- and homogeneous-charge engine operating conditions and a good agreement was obtained, substantiating the reliability of the applied computational model. Then, the effects of the injector protrusion in the combustion chamber and of injection timing were analyzed, and their impact on jet stability and mixture-formation process was analyzed.
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Caprioli, Stefano, Antonello Volza, Enrico Mattarelli, and Carlo Alberto Rinaldini. "High Performance and Near Zero Emissions 2-Stroke H <sub>2</sub> Engine." In 16th International Conference on Engines & Vehicles. SAE International, 2023. http://dx.doi.org/10.4271/2023-24-0068.
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<div class="section abstract"><div class="htmlview paragraph">The paper presents a preliminary study on a virtual 2-stroke 3-cylinder 0.9 L DI SI supercharged engine running on Hydrogen (H<sub>2</sub>), able to meet both high performance targets and ultra-low emissions limits (NOx&lt;20 ppm). Combustion is similar to a conventional 4-stroke H<sub>2</sub> DI engine, while the design of the cylinder and the actuation law of both intake and exhaust valves are specifically optimized for the 2-stroke cycle. In comparison to a more conventional 2-stroke loop scavenged engine, with piston-controlled ports, the use of poppet valves enables a more flexible control of the gas exchange process and to maintain the same design of a 4-stroke engine for pistons, cylinders block, crankcase and lubrication system. On the other hand, it is more difficult to avoid the short-circuit of the fresh charge, while permeability of the valves becomes quite critical at high engine speed. Therefore, particular care was devoted to the optimization of the intake and exhaust ports geometry, as well as to the valves actuation law. While the development of the scavenging system was mainly supported by CFD-3D simulation, the optimization of the supercharging system is driven by 1D analyses (by GT-Power). Three different supercharging configurations have been analyzed, with different levels of complexity, performance and cost: compact mechanical supercharger, controlled by a by-pass valve; variable geometry turbocharger, assisted by a mechanical supercharger and controlled by a by-pass valve; variable geometry turbocharger, assisted by an electric supercharger. The 1D engine model of the 2-stroke engine is derived as closely as possible from the experimentally calibrated model of a 4-stroke H<sub>2</sub> prototype. In particular, the virtual engines share the setup of the predictive combustion and emissions models.</div></div>