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Variable Valve Actuation and Dual-Fuel Combustion Master’S Thesis

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Variable Valve Actuation and Dual-Fuel Combustion Master’S Thesis Aalto University School of Engineering Department of Energy Technology Variable Valve Actuation and Dual-Fuel Combustion Master’s Thesis 3.8.2015 Juhani Törmänen Supervisor: Prof. Martti Larmi Instructor: Lis. Sc. (Tech.) Teemu Sarjovaara Aalto University, P.O. BOX 11000, 00076 AALTO www.aalto.fi Abstract of master's thesis Author Juhani Törmänen Title of thesis Variable Valve Actuation and Dual-Fuel Combustion Degree programme Energy Technology Major/minor Personal minor Code K9002 Thesis supervisor Prof. Martti Larmi Thesis advisor(s) Lis. Sc. (tech.) Teemu Sarjovaara Date 03.08.2015 Number of pages 85 Language English Abstract The constantly increasing interest in alternative fuels in transportation has given birth to new strategies in the internal combustion engine technology. The tightening emissions regulations further boost this development. The dual-fuel technology is one of the most promising new concepts for natural gas-fuelled engines and it has already been widely adopted by the marine and power generation industry. However, the transition from Diesel to dual-fuel engines in road and off-road traffic has not been as rapid. The relatively high hydrocarbon emissions are one of the drawbacks that hinder the use of dual-fuel engines. This Master’s thesis focuses on combustion and emissions research in a dual-fuel research engine with VVA. VVA is commonly used in passenger car engines but rarely in heavy-duty Diesel engines, even though it offers some indisputable benefits. Five different valve actuation profiles were used with several Diesel substitution rates. The effects of each parameter combination on the cylinder pressure and engine-out emissions were recorded. The analysis of the engine phenomena was mainly based on calculations utilizing the cylinder pressure data. The research engine was a conventional Diesel engine converted to run in dual-fuel mode. The conversion included a new exhaust system, methane feed line including injectors, several new sensors and other devices related to the methane injection. Moreover, the engine control system was updated for dual-fuel operation. The results of the engine tests can be concluded as follows: The dual-fuel combustion is very sensitive to IEGR, most likely due to high mixture temperature. High temperatures promote the partial pre-combustion oxidation of methane which causes a substantial increase in the heat release rate even with very lean mixtures. Low temperatures have the opposite effect, although it is not as pronounced. A significant amount of the HC emissions originate from the scavenging if methane is injected prior to the exhaust valve closing. Furthermore, high substitution ratios tend to increase the cycle-to-cycle variation. Keywords dual-fuel, gas engines, alternative fuels, variable valve actuation Aalto-yliopisto, PL 11000, 00076 AALTO www.aalto.fi Diplomityön tiivistelmä Tekijä Juhani Törmänen Työn nimi Muuttuva venttiiliajoitus ja dual-fuel-palaminen Koulutusohjelma Energiatekniikka Pää-/sivuaine Henkilökohtainen sivuaine Koodi K9002 Työn valvoja Professori Martti Larmi Työn ohjaaja(t) Tekniikan lisensiaatti Teemu Sarjovaara Päivämäärä 03.08.2015 Sivumäärä 85 Kieli Englanti Tiivistelmä Jatkuvasti kasvava kiinnostus vaihtoehtoisia polttoaineita kohtaan liikennekäytössä on synnyttänyt uusia lähestymistapoja polttomoottoritekniikassa. Kiristyvät päästömääräykset yhä vauhdittavat tätä kehitystä. Dual-fuel-teknologia on yksi lupaavimmista uusista maakaasua hyödyntävistä moottorikonsepteista ja se onkin saavuttanut jo vankan jalansijan merenkulku- ja voimalaitostekniikassa. Tieliikenne- ja työkonekäytössä muutos ei kuitenkaan ole ollut näin nopeaa. Verrattain korkeat hiilivetypäästöt ovat yksi dual-fuel-moottoreiden yleistymistä haittaavista tekijöistä. Tämä diplomityö paneutuu palamisen ja päästöjen tutkimukseen muuttuvalla venttiiliohjauksella varustetun dual-fuel-tutkimusmoottorin avulla. Muuttuvaa venttiiliohjausta käytetään yleisesti henkilöautojen moottoreissa, mutta varsin harvoin raskaan kaluston puristussytytteisissä moottoreissa. Tässä työssä käytettiin viittä erilaista venttiiliohjausstrategiaa ja useita eri korvaavuusasteita. Jokaisen yhdistelmän vaikutukset palamiseen ja päästöihin tallennettiin. Tutkittujen ilmiöiden analyysi pohjautui pitkälti sylinteripainetietoon ja sitä hyödyntäviin laskelmiin. Tutkimusmoottori oli dual-fuel-käyttöiseksi muunnettu Diesel-moottori. Muunnos sisälsi muun muassa uuden pakokaasujärjestelmän, metaanisyötön laitteineen, useita uusia antureita sekä muista metaanin ruiskutukseen liittyviä laitteita. Lisäksi moottorin ohjausjärjestelmä päivitettiin dual-fuel-järjestelmää ja mittauksia varten. Tutkimuksen tuloksista voidaan nostaa esille useita pääkohtia: Dual-fuel-palaminen on hyvin herkkä sisäiselle EGR:lle, mikä todennäköisesti johtuu seoksen lämpötilan noususta. Korkea lämpötila edistää metaanin osittaista hapettumista ennen varsinaista palamista, mikä puolestaan lisää huomattavasti seoksen palamisnopeutta myös hyvin laihoilla seoksilla. Matalilla lämpötiloilla on päinvastainen vaikutus, vaikka vaikutus on huomattavasti vähäisempi. Merkittävä osa hiilivetypäästöistä syntyy kaasunvaihdon aikana, jos metaani ruiskutetaan ennen pakoventtiilin sulkeutumista. Korvaavuusasteella vaikuttaisi olevan syklistä variaatiota lisäävä vaikutus. Avainsanat dual-fuel, kaasumoottorit, vaihtoehtoiset polttoaineet, muuttuva venttiiliajoitus Preface This thesis was conducted in the Aalto University Internal Combustion Engine Laboratory. The project was funded by the Henry Ford Foundation in Finland and by the Aalto University Department of Energy Technology. I want to thank these organizations for the financial aid. I am particularly grateful to my instructor Lis. Sc. Teemu Sarjovaara and my supervisor Professor Martti Larmi for the opportunity to write this thesis. I also want to express my gratitude to the following people that have helped me during my work in the laboratory: Otto Blomstedt, Olli Ranta, Rasmus Pettinen, Alberto Murillo, Tuomo Hulkkonen, Kari Hujanen and Karri Keskinen. Finally, I thank my friends and family for all the support in my studies and in my life outside the university. Hyvinkää, May 2015 Juhani Törmänen i Table of Contents 1 Introduction ........................................................................................ 1 2 Background ....................................................................................... 2 2.1 Natural Gas as Diesel Fuel Substitute in Dual-Fuel Engines ............. 2 2.1.1 Dual-Fuel Engine Fundamentals ............................................. 2 2.1.2 Heavy Duty Gas Engine Emissions Legislation ...................... 4 2.1.3 Dual-Fuel In-Cylinder Mixture Formation and Combustion ..... 6 2.1.4 Natural Gas Fuel Properties .................................................... 9 2.2 Current Technology, Problems and Solutions ................................. 11 2.2.1 Dual-Fuel Retrofitting ............................................................ 11 2.2.2 Dual-Fuel Emissions After-Treatment ................................... 15 2.2.3 Current Problems in Dual-Fuel Engines ................................ 17 2.3 Dual-Fuel Engine Emission Formation and Causes ........................ 19 2.3.1 Nitrogen Oxides .................................................................... 19 2.3.2 Unburned Hydrocarbons ....................................................... 21 2.3.3 Carbon Monoxide .................................................................. 23 2.3.4 Particulate Matter .................................................................. 24 2.4 Variable Valve Actuation Strategies ................................................ 25 2.4.1 Variable Valve Actuation ....................................................... 25 2.4.2 Miller Cycle ........................................................................... 27 2.4.3 Valve Overlap and Exhaust Valve Actuation ......................... 29 3 Research System and Methods ...................................................... 30 3.1 System Overview and Measurements ............................................. 30 3.1.1 General Overview of the Research System .......................... 30 3.1.2 Simulink Model and dSpace .................................................. 32 3.1.3 Measurement Tools and Sensors ......................................... 33 3.2 Methane Feed System .................................................................... 34 3.2.1 Methane Injection .................................................................. 34 3.2.2 Methane Injection Control ..................................................... 36 3.2.3 Methane Feed Problems ....................................................... 38 3.3 Research Parameters and Data Handling ....................................... 39 3.3.1 Research Parameters and Design of Experiments ............... 39 3.3.2 Valve Timing Configurations ................................................. 40 3.3.3 Data Processing and Calculations ........................................ 42 ii 3.3.4 Uncertainties Related to Measurements and Calculations .... 44 4 Experiment Results and Analysis .................................................... 46 4.1 Boundary Conditions ....................................................................... 46 4.1.1 Engine Parameters ............................................................... 46 4.1.2 Variable Valve Actuation Curves ........................................... 48 4.2 Cylinder Pressures .........................................................................
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