Browsing by Author "Larmi, Martti"

Filter results by typing the first few letters
Now showing 1 - 20 of 173
  • 2D Diesel Spray Droplet Size Mapping Based on Planar Laser Induced Fluorescence and Mie-Scattering Technique Using Sparsity Deconvolution
    (2024-04-09) Cheng, Qiang; Grahn, Viljam; Akram, Muhammad; Hyvonen, Jari; Kaario, Ossi; Larmi, Martti
     A4 Artikkeli konferenssijulkaisussa
    The distribution of spray droplet sizes plays a pivotal role in internal combustion engines, directly affecting fuel-air mixing, evaporation, and combustion. To gain a precise understanding of droplet size distribution in a two-dimensional space, non-intrusive optical diagnostics emerge as a highly effective method. In the current investigation, two-dimensional (2D) diesel spray droplet sizes mapping using a simultaneous combination of planar laser-induced fluorescence (PLIF) and Mie-scattering techniques is introduced. The assessment of droplet diameter relies on the interplay between fluorescent and scattered light intensities which correspond the light based on volumetric droplets and surface area of the droplets. This calculation is made possible through the LIF/Mie technique. However, traditional LIF/Mie methods are plagued by inaccuracies arising from multiple light scattering. To overcome this challenge and to attain higher accuracy than conventional LIF/Mie technique, we introduce a sparsity deconvolution approach to eliminate unwanted light interference on both LIF and Mie images. The core concept of sparsity deconvolution is to reduce disturbances caused by multiple scattering and offer sharp and finely detailed images for LIF/Mie ratio estimation. To enhance spatial sharpness and remove the undesired scattering light, an iterative Richardson-Lucy (RL) and Land Weber (LW) filters are introduced for image deconvolution. The results reveal that RL deconvolution is particularly well-suited for the intricate task of deconvolving complex liquid sprays, producing sharper and finer detailed droplet images. Additionally, the further calibration of 2D droplet size mapping based on microscopic method is implemented to approximate the linear fitting curve of dependence between macro LIF/Mie ratio and droplet diameter. This comprehensive approach advances the understanding of the critical role played by droplet size distribution under engine-like conditions.
  • Acoustic simulation of a tractor engine exhaust system
    (2013) Rodriguez, Alvaro
     School of Engineering | Master's thesis
    This thesis focuses on the acoustic simulation of an agricultural engine. Its aim was to modify the noise emissions of a tractor diesel engine by making parameter changes on the exhaust line. Research about acoustic emissions from engines and a suitable software tool, available to simulate acoustics of the exhaust line is also included. Noise legislation existing today for tractors does not present big challenge for tractors having a cabin so the principal goal for developing the acoustics in the present study focuses on satisfy driver comfort and customer demand. A simulation model of the VALTRA N-Series 4-stroke, 4-cylinder, 4.9L has been built taking into account the intake and exhaust system. Whole simulation was carried out by way of I-D fluid dynamics utilizing the software GT ·Power 7.3. The turbo model was scaled from a 3.5L engine due to the exact engine turbo map was not available. The tractor model was validated by means of experimental data measured along the intake and the exhaust system using high frequency pressure sensors and at the exhaust outlet utilizing a microphone. Elementary modifications like exhaust pipe diameter, length and bend variations were analysed. Furthermore the acoustic damping effect of the existing components in the exhaust pipe was determined and new components like resonators were included. Acoustical performance of the system is presented in terms of sound pressure level emitted by the exhaust outlet. The results of this study show that the importance of exhaust pipe design on noise emissions and how the model behaves to elementary changes. In particular exhaust pipe diameter has a critical influence on the acoustic emissions and it was the only parameter which produced significant variations at the low frequency range.
  • Adaptive Boost Pressure Control for Four-Stroke Diesel Engine Marine Application in the Presence of Dynamic Uncertainties
    (2019-01) Samokhin, Sergey; Hyytiä, Jari; Zenger, Kai; Ranta, Olli; Blomstedt, Otto; Larmi, Martti
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Robustness of the control system in marine engines with respect to its time-varying dynamics has recently become an important research topic. The variation of dynamics, caused primarily by the mechanical wear of components or their faults originating from tough operating condition, can lead to the overall control system instability (or marginal stability, depending on how severe the variation is). The biggest issue is that the marine engines cannot always be fixed fast enough (especially on large cargo vessels, spending hundreds of hours cruising). In this paper, a control adaptation (indirect model-reference adaptive control) is proposed to deal with the engine parameter variation in a way that the original system response is preserved. The stability and robustness of the proposed control system are studied by means of numerical simulations. Finally, the performance of the control concept is validated on the medium-speed diesel engine test bed at constant speed under load transients. Superior performance compared with fixed-parameter proportional-integral control is demonstrated.
  • Advanced heat transfer modelling with application to internal combustion engine CFD simulations
    (2011) Nuutinen, Mika
     School of Engineering | Licentiate thesis
    At present, majority of the detailed modelling related to engine performance, gas flow, combustion, and emissions is performed with Computational Fluid Dynamics (CFD) simulations. The Reynolds Averaged Navier Stokes (RANS) turbulence models are most widely utilized due to turbulent flow conditions, complex geometries, and complicated sub models. Although Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) are more accurate than RANS models, their application in engineering simulations is often limited due to high computational costs. Available heat transfer modelling options utilized with RANS turbulence models comply poorly with engine flows. They are either completely inadequate for the particular flow conditions, or their validity requirements may multiply the problem size and computational costs. The work in this thesis concentrates on development of an accurate, engine flow compliant heat transfer I near wall modelling formalism within RANS framework. The model development yields reformulation of the whole near wall treatment, intrinsically improving the entire near wall accuracy of utilized turbulence models. Furthermore, the developed models are universal and by no means restricted to engine simulations alone. This thesis comprises a survey of the research field and three attached original publications. The first publication presents numerical wall function formalism designed to include effects of strong temperature gradient induced density variation on wall heat and momentum transfer models. The objective was to study conjugate heat transfer from charge gas to piston material in order to get estimates for piston surface temperatures and heat loss. The results indicated that the near wall density variation has a significant effect on peak surface temperature and overall heat transfer predictions. The following research indicated that the temperature gradient induced variations of charge gas viscosity, conductivity, and heat capacity affect the heat transfer prediction as well. Furthermore, this new formalism facilitates rigorous computation of the turbulence model source terms in the near wall region. These source terms affect the near wall turbulence level, strongly coupled with the heat and momentum transfer models. Following these ideas in two subsequent publications, advanced models were developed and implemented. A commercial CFD software, Star-CD, extensively utilized in internal combustion engine CFD simulations, was used as a primary platform for model development and simulations. In addition, an in-house CFD solver was programmed for model testing and validation. This thesis contributes to the research field by providing a comprehensive theoretical approach to heat transfer related near wall modelling within RANS framework and complete theory based models directly applicable to engineering CFD simulations.
  • Ahtoilman jäähdyttäminen 2-portaisesti ahdetussa työkonedieselmoottorissa
    (2017-10-30) Linna, Antti
     Insinööritieteiden korkeakoulu | Master's thesis
    Työssä tutkittiin teorian sekä käytännön mittausten kautta 2-portaisesti ahdetun työkonedieselmoottorin turboahtamista ja ahtoilman välijäähdytyksen vaikutuksia moottorin suoritusarvoihin. Työssä edetään turboahtamisen teorian kautta tutkimuksiin, tulosten analysointiin ja johtopäätöksiin. Ensisijainen tutkimuskohde oli painevaiheiden välinen jäähdytys ja siihen tehtävät muutokset. Tutkimukset suoritettiin kolmella erilaisella järjestelmällä, joista ensimmäisessä painevaiheiden välinen jäähdytys oli toteutettu moottorin jäähdytinnesteellä eli HT-piirillä, toisessa erillisellä matalan lämpötilan LT-piirillä sekä kolmannessa kokonaan ilman painevaiheiden välistä jäähdytystä. LT-piirin vaikutuksia tutkittiin laajemmin jäähdytyspiirin eri tehovaihtoehdoilla. Jäähdytystä tutkittiin ilmiönä, eikä ollut tarkoitus kehittää laitteistoa painevaiheiden väliseen jäähdytykseen. Turboahtimien toiminta heijastuu koko polttomoottoriprosessiin, jota on analysoitu ahtoilman jäähdytyksen vaikutuksen kautta. Mittaustuloksia saatiin staattisten pisteiden ja dynaamisten tilanteiden muodossa, joten moottorin toimintaa pystyttiin arvioimaan kokonaisuudessaan. Mittaukset onnistuivat hyvin ja tulokset tukivat odotetusti teoriaa. Tulokset auttoivat ymmärtämään termodynamiikan vaikutuksia koko polttomoottoriprosessiin. Tutkimusten johtopäätöksenä voidaan todeta, että LT-piirin käyttö ahtoilman välijäähdyttämisessä alentaa moottorin polttoaineen kulutusta staattisissa tilanteissa ja parantaa kuormannostokykyä. Suorituskyvyn kannalta LT-piirin käyttö mahdollistaa parhaat edellytykset moottorin toiminnalle. Ilman painevaiheiden välistä jäähdytystä oleva järjestelmä parantaa moottorin kuormannostokykyä, mutta huonontaa suurten akselitehojen polttoaineen kulutusta ja rajoittaa moottorin suurinta tehotiheyttä korkeapainekompressorin lämpötilan pitämiseksi sallituissa rajoissa.
  • Ajoneuvojen hiukkaspäästöt ja niiden mittaus
    (2018-04-22) Ojanen, Katriina
     Insinööritieteiden korkeakoulu | Bachelor's thesis
  • Alternativa dieselbränslen och avgasefterbehandling
    (2017-05-02) Ehrs, Alexander
     Insinööritieteiden korkeakoulu | Bachelor's thesis
  • Application of Synthetic Renewable Methanol to Power the Future Propulsion
    (2020-09-15) Santasalo-Aarnio, Annukka; Nyari, Judit; Wojcieszyk, Michal; Kaario, Ossi; Kroyan, Yuri; Magdeldin, Mohamed; Larmi, Martti; Järvinen, Mika
     A4 Artikkeli konferenssijulkaisussa
    As CO2 emissions from traffic must be reduced and fossil-based traffic fuels need to phase out, bio-based traffic fuels alone cannot meet the future demand due to their restricted availability. Another way to support fossil phase-out is to include synthetic fuels that are produced from circular carbon sources with renewable energy. Several different fuel types have been proposed, while, methanol only requires little processing from raw materials and could be used directly or as a drop-in fuel for some of the current engine fleet. CO2 emissions arising from fuel production are significantly reduced for synthetic renewable methanol compared to the production of fossil gasoline. Methanol has numerous advantages over the currently used fossil fuels with high RON and flame speed in spark-ignition engines as well as high efficiency and low emissions in combustion ignition engines. Feasible options for engine development or upgrading for methanol have been presented separately in the past work but not considering the whole value chain. The results indicate that high concentration methanol blends will increase significantly tank-to-wheel efficiency, lower energy consumption and CO2 emissions, while their volumetric fuel consumption will increase compared to gasoline, due to the low calorific content of methanol. The work visualizes the impact on CO2 emissions for methanol-fueled transport applications and overall suitability for propulsion. For marine sector, successful demonstrations reveal high maturity of engine technology using methanol fuel. This work also highlights further development needs of synthetic renewable methanol to become a sustainable future transport fuel.
  • Aviation Gas Turbine Combustors and Alternative Fuels
    (2022-04-27) Räisänen, Sylvi
     Insinööritieteiden korkeakoulu | Bachelor's thesis
  • Benchmarking medium speed natural gas engine for direct injected premixed charge combustion
    (2010) Nurmiranta, Jussi
     School of Engineering | Master's thesis
    In this master's thesis, the technical possibilities of building a direct injected premixed charge combustion system for medium speed natural gas engine are studied. The purpose of direct natural gas injection is to reduce the methane emission iii the exhaust gases and to be able to run the engine on different loads without the need for throttling the intake air flow. The objective of the work is to make a preliminary study of natural gas engine technology and to find suitable injector components which would enable optimum ignition and combustion conditions with lowest emissions. The conventional lean-burn natural gas engines with port fuel admission have high methane emission compared with stoichiometrically operated engines combined with methane oxidation catalysts. However, can-burn combustion offers significant efficiency benefits compared with stoichiometric combustion. Methane emission is currently not limited in large bore medium speed engines which are operated in the lean-burn combustion mode. The thesis consists of independent parts which cover natural gas characteristics, gas compression calculations, natural gas combustion methods, available natural gas engine technology, a review of direct injection gasoline engines, and investigation on available technology for natural gas direct injection. In addition, some fuel calculations are performed in order to define the injector dimensions. Finally some suggestions are made for building a medium speed direct injection natural gas engine. On the ground of the study, suggestion for building a medium speed direct injection natural gas engine is that outwardly opening tappet injector is the optimum choice for stratified charge operation. Lean-burn combustion with pilot diesel ignition is the target that should be pursued in order to minimize other emissions and have an easily constructible technical solution.
  • Benefits of digitalized asset management for steam turbines
    (2019-08-19) Kare, Lauri
     Insinööritieteiden korkeakoulu | Master's thesis
    Steam turbines are considered long-lived and require little attention during normal operation. Cost optimizations due to infrequent demand for turbine expertise, together with retiring workforce, have resulted in increasing shortage of know-how. Digitalization could substitute unavailable turbine resources, but the projects and investment have been challenging to initiate and incentivize. The objective of this thesis was to map the benefits of digitalized steam turbine asset management, what kind of challenges digitalization could mitigate and how the implementation could be facilitated. The research confirmed that turbine operating companies lack the domain know-how and resources required for some current systems and demands. Prolonging of overhauls and deficiencies in asset management, such as insufficient documenting and data utilization, were observed to be other main challenges. Increased downtime and unoptimized practices and systems reduce efficiency, usability, reliability and availability. Advanced diagnostics in condition monitoring systems could increase availability and reliability by enabling optimized condition-based maintenance and facilitate shorter overhauls by reducing unforeseen findings. Solutions and service that allow faster fact-finding in anomalies would increase availability as well. Asset management systems with more connectivity, centralization, user-friendliness and AI would reduce downtime by enhancing planning, documenting and spare part management. Such systems could also increase usability and the overall efficiency of operations and maintenance. Main hindrances for digitalization are the imbalance between costs and perceived added value, and insufficient focus on the usability of asset management systems. Development of advanced solutions in current business models is disincentivized. Long-term contracts could enable the implementation of best practices, reduce risks and incentivize higher quality of services. Partnership business models facilitate mutual benefits better than short-term and stand-alone services.
  • Biodiesel: uusiutuva biopolttoneste vai synteettinen diesel?
    (2015-04-29) Kuula, Joel
     Insinööritieteiden korkeakoulu | Bachelor's thesis
  • Biofuel blend late post-injection effects on oil dilution and diesel oxidation catalyst performance
    (2018-11-01) Tilli, Aki; Hulkkonen, Tuomo; Kaario, Ossi; Larmi, Martti; Sarjovaara, Teemu; Lehto, Kalle
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this article, the effects of different biofuel–diesel blends on engine oil dilution and diesel oxidation catalyst performance during late post-injections were investigated. The engine tests were made with an off-road diesel engine under low load conditions at 1200 r/min engine speed. During the experiments, oil samples were periodically taken from the engine oil and later analyzed. Emissions and temperatures before and after the diesel oxidation catalyst were also measured. The fuels studied were fossil EN590:2013 diesel fuel, 30 vol.% biodiesel (fatty acid methyl ester) and 30 vol.% hydrotreated vegetable oil, which is a paraffinic diesel fuel fulfilling the EN15940 specification. The novelty of the study is based on two parts. First, similar late post-injection tests were run with blends of both hydrotreated vegetable oil and fatty acid methyl ester, giving a rare comparison with the fuels. Second, oil dilution and the fuel exit rates during normal mode without the late post-injections were measured. The results showed the oil dilution and the diesel oxidation catalyst performance to be very similar with regular diesel and hydrotreated vegetable oil blend. With the fatty acid methyl ester blend, increased oil dilution, smaller temperature rise in the diesel oxidation catalyst and higher emissions were measured. This indicates that during diesel particulate filter regeneration by late post-injections, fatty acid methyl ester blends increase fuel consumption and require shorter oil change intervals, while hydrotreated vegetable oil blends require no parameter changes.
  • Biofuel legislation implications on biofuel markets in Finland, Sweden, and Norway
    (2020-05-18) Siirala, Aino
     Insinööritieteiden korkeakoulu | Master's thesis
    The EU has set targets for renewable energy share in transport and emission intensity reduction of fuels. One of the aims of these targets is to decrease emissions in transport. One way to achieve these targets is to supply biofuels to consumption. Each member state can choose the way of implementing these targets. Even though Norway is not an EU member state, it has agreed on implementing the targets in its national legislation. When biofuel legislation is implemented in a different way in each country’s national legislation, the valuation of biofuels and their attributes differs from country to country. This creates arbitrage in the biofuel market and may lead to intra-industrial trade of biofuels. The aim of this master’s thesis is to assess if the differences in the Finnish, Swedish, and Norwegian biofuel legislation create arbitrage and thus intra-industrial trade of biofuels. The emphasis is more on the operating environment created by national legislations. Therefore, the actual amounts of biofuels traded is out of the scope of this thesis. The differences in biofuel valuation in Finland, Sweden, and Norway are studied by estimating fuel suppliers’ willingness to pay for different types of biofuels when supplying biofuel to the market. As a result, the willingness to pay for biofuels fulfilling the biofuel obligation is highest in Finland and lowest in Norway. Furthermore, differences in biofuel sustainability characteristics valuation were found, implicating that the legislative environment is favourable for intra-industrial trade of biofuels.
  • Biofuels and their quality challenges during handling, transportation and storage in the supply chain
    (2017-10-30) Tellez, Adriana
     Insinööritieteiden korkeakoulu | Master's thesis
  • Biofuels in the fuel injection system of a medium-speed diesel engine
    (2008) Tilli, Aki
     Helsinki University of Technology | Master's thesis
    Tämän diplomityön taustalla on tarve luoda pohjaa polttomoottoritekniikan laboratorion tulevalle tutkimukselle arvioimalla nykyaikaisten uusiutuvien polttoaineiden toimivuutta yksisylinterisen, keskinopean tutkimusmoottori EVE:n ("Extreme Value Engine") polttoaineensyöttöjärjestelmässä. Tavoitteena on selvittää, tarvitseeko bioperäisten dieselpolttoaineiden käyttöön siirryttäessä tehdä muutoksia moottorin polttoaineensyöttöjärjestelmään. Työ koostuu kirjallisuusosiosta, teoriaosuudesta, simulaatiomallin ja simulaatioiden esittelystä, sekä tuloksien esittelystä ja yhteenvedosta. Kirjallisuusosassa esitellään tavanomainen dieselpolttoaine sekä uusiutuvia dieselpolttoaineita. Esiteltävät polttoaineet ovat perinteinen biodiesel (rasvahappometyyliesteri, FAME), vetykäsitelty kasviöljy (HVO), Fischer-Tropsch (FT) - dieselpolttoaineet ja dimetyylieetteri (DME). Polttoaineiden raaka-aineet, tuotanto ja ominaisuudet esitellään lyhyesti sekä niiden käytettävyyttä ja laatua vertaillaan. Työn teoriaosuudessa työssä käytetty ohjelmisto, GT FUEL, esitellään lyhyesti. Simulaatiomallin perusperiaatteet ja ratkaisumenetelmät selitetään. Tärkeimmät polttoainejärjestelmän laskennassa käytetyt teoriat, kaavat ja analogiat käydään läpi. Simulaatio-osuudessa esitellään ensin osana diplomityötä tehty simulaatiomalli sekä tehdyt simulaatiot mallin sovittamiseksi mittaustuloksiin ja biopolttoaineiden vertailemiseksi. Tulokset ja polttoaineiden muu oletettu käyttäytyminen polttoaineensyöttöjärjestelmässä esitellään seuraavaksi. Simulaatioiden mukaan tutkitut bioperäiset dieselpolttoaineet käyttäytyvät EVE:n polttoainejärjestelmässä varsin samankaltaisesti. Fysikaalisista ominaisuuksista lähinnä tiheyden eroavaisuuksilla on ennustettavia vaikutuksia järjestelmän toimivuuteen. Kemialliset ominaisuudet lienevätkin tärkeämpiä itse polttoaineensyöttöjärjestelmän toiminnan kannalta. Polttoainesuihkun käyttäytyminen ja biopolttoaineiden palaminen ovat tärkeitä tutkimuskohteita ja siten seuraava askel kun tutkitaan biopolttoaineiden soveltuvuutta tutkimusmoottori EVE:en.
  • Blandning av väte i naturgas som bränsle för gasmotorer
    (2015-11-23) Berg, Hanna
     Insinööritieteiden korkeakoulu | Master's thesis
    Väte-naturgasblandningar analyseras i rapporten som bränsle för gasmotorer. Till rapporten hör planering av tester, utförning av tester och analys av testresultat samt slutsatser. Blandning av väte i gassystemet kan komma att bli verklighet inom nära framtid, och vätemotorer har redan testats i stor utsträckning. För att kunna använda väteblandningar i förbränningsmotorer bör inverkan på knackning och förbränningsvaraktighet analyseras. Eftersom väte brinner snabbare än metan kommer även blandningarna att brinna snabbare, med risk för ohanterlig knackning eller förtändning. I rapporten läggs vikt vid planeringen av säkerheten i testningsutrymmet, för att garantera säker operation av motorn under testerna. Testerna utfördes på Wärtsiläs medelsnabba gasmotorer, en med pilottändning och en med tändstiftständning, där både full och nedsatt last analyserades med varierande mängd väte. Tändningstidpunkten varieras för att analysera när den optimala tidpunkten är för de olika blandningarna. Högsta möjliga andelen väte som kan tilläggas i bränslet på full last var för tändstiftmotorn 28 vol-% på medelhögt kompressionsförhållande och 16 vol-% på motorn med pilottändning på högt kompressionsförhållande. Med lägre kompressionsförhållande kunde mera väte tilläggas, och med 75 % last kunde 60 vol-% väte tilläggas i bränslet. Mera än detta kunde ha körts från knackningssynpunkt, men systemet kunde inte mata högre än detta. Inga justeringar gjordes i motorn vid dessa punkter. Punkterna hade höga NOx-nivåer, vilket beror på den höga temperaturen i cylindern. När tändningstidpunkten justerades kunde mera väte tilläggas, och NOx-nivån sjönk. Kolväte-utsläppen minskade, speciellt på tändstiftsmotorn vid höga andelar väte. Resultaten visar att Wärtsiläs motorer kan köras på relativt hög andel väte om tändningstidpunkten justeras. Utan justering i tändningstidpunkt är trycken och temperaturerna i motorn omöjligt höga och ger upphov till höga NOx-utsläpp. Vid optimal tändningstidpunkt kommer flera fördelar fram, som lägre kolväte-utsläpp. Framtida forskningsmöjligheter finns i att köra tester med dessa bränslen på varierande last. För att väte ska kunna tilläggas i gasnätverket för Wärtsiläs del borde ett verktyg för att kontinuerligt analysera inkommande gas till motorn utvecklas, så tändningstidpunkten kan justeras snabbt.
  • Blending Behavior of Hydrocarbon and Oxygenate Molecules to Optimize RON and MON for Modern Spark-Ignition Engines (SI)
    (2020-09-15) Knuutila, Lotta; Kaario, Ossi; Larmi, Martti; Santasalo-Aarnio, Annukka; Karvo, Anna; Kiiski, Ulla
     A4 Artikkeli konferenssijulkaisussa
    Gasoline blending is known to be complicated, because individual gasoline fractions with different octane numbers, Research Octane Number (RON) or Motor Octane Number (MON) do not always blend linearly. Instead, they may blend non-linearly, in a synergistic or antagonistic manner. Even though RON and MON are regulated properties, linear and non-linear octane blending is not a broadly understood topic. The target in the developing process of a modern SI engine is to have 100% combustion efficiency which would lead to the reduction of hydrocarbon and carbon monoxide emissions. Therefore, the properties of gasoline, especially RON and MON, need to be optimized to ensure proper ignition in the engine and prevent harmful autoignition reactions. There are hundreds of hydrocarbons in gasoline which have different octane numbers (ON). The explanations for these variations are the structural differences in hydrocarbon molecules that influence on their reactivity. For instance, longer n-paraffins have lower octane numbers compared to aromatics where electrons are delocalized around their ring which increases stability of aromatics and thus, ON. In this paper, we report and visualize qualitatively the octane blending behaviour of different hydrocarbon and oxygenate molecules to facilitate gasoline components mixing to produce high quality gasoline for clean combustion. The present study shows ethanol to blend non-linearly, but synergistically with paraffins and olefins, while the blending with aromatics is antagonistic. We also conclude that oxygenate molecules such as furans and cyclic ketones, blend synergistically with hydrocarbons. However, predicting the ON of end gasoline is challenging, as gasoline is not a blend of two components, but rather a blend of many isomers and functional groups. Therefore, in this study we highlight the need for more complex blending models than binary ones.
  • Characterization and optical imaging of dual-fuel combustion
    (2017-12-11) Aryal, Janak
     Insinööritieteiden korkeakoulu | Master's thesis
    As the regulations for engine-out emissions around the world are getting increasingly stringent, dual-fuel (DF) combustion involving natural gas or methane as primary fuel ignited by a very small diesel pilot can be an attractive alternative to diesel only combustion in heavy duty engines of both road as well as marine applications. Natural gas or methane have potential for reduction of carbon dioxide emissions because of their high hydrogen to carbon ratio compared to diesel fuel. Their highly premixed combustion also produces less NOx than diesel as the overall combustion temperature is lower. Furthermore, they have huge potential for exploitation at competitive prices in regions such as India, China and North America, thus helping to reduce dependency on conventional diesel and gasoline. In this thesis work, an attempt has been made to characterize the DF combustion of premixed methane and diesel pilot with the help of optical and thermodynamic measurements. DF combustion experiments were carried out in a single cylinder, optical research engine with electro hydraulic valve actuation system and custom made engine control program that enable research with great degree of parameter freedom. Crank angle resolved images of Natural Luminosity (NL) resulting from combustion were acquired using a high speed CMOS camera. NL signals showing the development of premixed flame fronts, cylinder pressure traces, heat release rate (HRR) profiles and ignition delays are considered as tools for characterizing the DF combustion in this thesis work. Influences of methane lambda (λCH4), of pilot fuel ratio (PR) and of charge air temperature on dual-fuel combustion were investigated separately using three different case studies. From optical and thermodynamic investigations, it was observed that the ignition delay and shape of HRR in DF combustion strongly depend upon lambda of the gaseous fuel. With methane substitution rate ranging from 82% to 88%, when λCH4 was varied from 1.1 to 1.9, it was observed that the periods of ignition delays were longer at both least as well as most lean case, with relatively shorter delays around the λCH4 1.5 region. The study of DF combustion as a function of PR revealed that the DF ignition delay decreased with increasing PR until a certain extent after which any increase in PR did not bring the ignition delay significantly forward. In the final case study, for both λCH4 1.1 and λCH4 1.8 cases, it was observed that higher intake temperatures shortened ignition delays, promoted second stage combustion and reduced cycle-to-cycle variations. However, at high intake temperatures, certain DF cycles also demonstrated excessive rates of pressure rise immediately after the onset of combustion. In summary, it is concluded that at high substitution rates (ca. 85%) and light load conditions as experimented in this thesis, DF combustion is dominated by the premixed flame front propagation mode rather than by the characteristics of diesel diffusion combustion.
  • Kemiallinen tasapaino dieselprosessissa
    (2000) Tiainen, Jukka
     Helsinki University of Technology | Master's thesis
    Työn tarkoituksena oli tutustua dissosiaation vaikutuksiin dieselprosessissa. Dissosiaatiolla tarkoitetaan kemiallisten yhdisteiden hajoamista lämpötilan vaikutuksesta. Tämä johtaa siihen, että polttomoottorin palotilassa on palamisen aikana huomattavasti enemmän kaasukomponentteja kuin stökiömetrisen palamisyhtälön mukaan laskettaessa. Näiden komponenttien muodostuminen ja hajoaminen vaikuttaa myös palotilan lämpötilaan ja paineeseen, sillä dissosiaatioreaktiot vaikuttavat kaasun sisäenergiaan ja moolimäärään. Dissosiaatioreaktioiden seurauksena syntyvää kaasun koostumusta selvitettiin kemiallisen tasapainon oletuksen avulla. Tämä yksinkertaistus ei täysin pidä paikkaansa, varsinkaan typen oksidien osalta, mutta helpottaa ja tehostaa laskentaa huomattavasti. Dissosiaatioreaktioiden laskentaa ei aiemmin ole liitetty useimpiin laskentamalleihin, sillä sen merkitys on arvioitu suhteellisen pieneksi. Työssä käytettiin nolladimensioista kaksivyöhykemallia, jossa sylinteriprosessin mallinnus on melko yksinkertainen, mutta kuitenkin sopiva ilmiön toimintaan ja vaikutuksiin tutustumiseen. Päästöjä laskevat alimallit, esimerkiksi typen oksidien osalta, ovat sinällään jo melko pitkälle kehittyneitä, mutta kriittistä niiden toiminnalle on ympäristö, jossa niitä sovelletaan. Jotta malleilla saataisiin hyviä tuloksia, on kaasun koostumus ja lämpötila palotilan vyöhykkeissä, sekä sylinteripaine oltava riittävän hyvin mallinnettu. Dissosiaation lisäämisellä pyrittiin parantamaan myös näitä asioita paremman tuloksen saamiseksi NO:n muodostukselle. Dissosiaation vaikutukset laskettuihin lämpötiloihin ja sylinteripaineeseen jäivät suhteellisesti melko pieniksi, eikä työssä näin ollen saavutettu merkittävää parannusta mallin laskentatarkkuuteen. Palotilan kaasuseokselle saatiin laskettua tarkempi koostumus ja sen perusteella saatiin kohtuullisen hyviä tuloksia NO:n muodostumiselle. Tulokset kuitenkin osoittivat, että päästöjen ennustamiseksi luotettavasti täytyy sylinteriprosessin laskentamallia vielä kehittää tarkemmaksi.