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Avgasbromsning Med Variabel Turbingeometri: Utformning av bypassventil för reglering av turbininloppstryck
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
2008 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Exhaust Braking With Variable Geometry Turbine (English)
Abstract [sv]

Detta arbete undersöker möjligheten att avgasbromsa med en turbo utrustad med variabel turbingeometri (VGT). Då många av Scanias motorer är utrustade med VGT-turbo innebär detta att det skulle kunna ges möjlighet till att rationalisera bort avgasbromsspjället till fördel för VGT-bromsning.

Konceptet som skall undersökas är att reglera turbininloppstrycket med en bypassventil förbi turbinen, likt en extern wastegate.

För att dimensionera denna bypassventil inför tillverkning samt för att undersöka bypassventilens inverkan på motorn utfördes simuleringar i GT-Power. Därefter validerades konceptet med VGT-bromsning och bypassventil i motorprov på en Scania V8. Resultaten från motorprovet visar på en mycket god avgasbromsprestanda. Med en självöppnande bypassventil vid 2400 rpm, helt stängd VGT erhålles 6,3 bar turbininloppstryck vilket resulterar i en bromseffekt på 360 kW ISO-netto och ca 16 kg/min i luftmassflöde genbom motorn. Denna lösning påvisar lika god prestanda som dagens avgasbroms med spjäll. Att reglera turbininloppstrycket med en bypassventil går även det mycket bra. Fördelen med att avgasbromsa med VGT:n visar sig vara att man får ett massflöde genom motorn som är ungefär dubbelt så högt jämfört med avgasbromsning med spjäll. Vad som däremot innebär svårigheter är det faktum att man för vissa driftspunkter befinner sig på god turbin och kompressorverkningsgrad, vilket kan innebära ett högt laddtryck vid vissa driftspunkter. Ett högt turbininloppstryck i kombination med detta laddtryck visar sig innebära begränsningar då fria ventillyft hos avgasventilen uppträder, vilket resulterar i höga cylindertryck.

Abstract [en]

This thesis work is investigating the possibility to exhaust brake using a turbo with variable turbine geometry (VGT). Today, several Scania engines are equipped with VGT which means that an exclusion of the exhaust brake used today would be possible in favour to VGT-braking.

The concept which is going to be investigated in this thesis is VGT-braking and using a bypass valve, similar to an external wastegate to control the turbine inlet pressure. To investigate how this bypass construction affected the engine and as a tool to dimension the geometry of the bypass valve, simulations were made in the engine simulation software GT-Power. These results founded the base for the specification of requirements that resulted in the bypass valve used in this test. The concept VGT-braking with a bypass valve was evaluated in an engine test on a Scania V8 engine. The results from this test show that this concept delivers the same performance as today’s engine brake and that is possible to control the turbine inlet pressure with a bypass valve like the one used in this test. With the self opening bypass valve we achieve at 2400 rpm 6,3 bar in turbine inlet pressure and 360kW ISO-net braking power and have approx. 16 kg/min mass flow through engine. The benefit of VGT-braking compared to today’s exhaust brake is the substantially higher mass flow through the engine, about twice as high. On the other hand, the fact that we get an increase in boost for certain points where we have a high compressor and turbine efficiency. A high turbine inlet pressure in combination with a high boost may cause difficulties related to valve lifts that is not caused by the camshaft. This means that we get very high cylinder pressures. All in all, this concept looks very promising according to performance and the design could be made pretty simple with in the best case a reduction of engine parts.

Place, publisher, year, edition, pages
, MMK 2008:3 MFM116
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-100187OAI: diva2:542944
Available from: 2012-08-06 Created: 2012-08-06 Last updated: 2012-08-06Bibliographically approved

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