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Injector Nozzle Hole Parameters and their Influence on Real DI Diesel Performance
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

A modern diesel engine is capable of running efficiently with low exhaust gas emissions over a wide operating range. This is thanks to techniques such as turbocharging, EGR, charge air cooling and an advanced fuel injection process. The fuel injection process is important for the combustion and emission formation in the diesel engine. The fuel injector has to atomize and vaporize the fuel as it is injected. During the combustion the emission formation has to be kept to a minimum. Very strong pressure gradients are present in a modern diesel injection nozzle, this causes cavitation to occur in the nozzle holes. The influence of cavitation on flow parameters such as the various discharge coefficients is discussed. The occurrence of cavitation helps the spray break up and it can keep the nozzle holes free from deposits. Excessive amounts of cavitation can lead to hole erosion and thus impact the long term operation of the nozzle in a negative way. Hole erosion as well as other mechanisms can cause hole to hole variations in fuel spray impulse, mass flow, penetration etc. This is a very important issue in any low emission diesel engine, especially during transients, as less than optimal conditions have to be handled. The influence of hole to hole variation on fuel consumption and emissions is not very well known and this thesis contributes to the field. As a part of this work a fuel spray momentum measurement device was developed and tested. Any automotive engine needs to be able to perform quick transitions between different loads and speeds, so called transients. In a turbocharged diesel engine with EGR issues related to the turbocharger and the EGR-circuit arise. A diesel engine has to run with a certain air excess in order to achieve complete combustion with low emissions of soot. When turbocharging is used the turbocharger turbine uses some of the exhaust enthalpy to drive the turbo compressor, in this way the engine is provided with boost pressure. In order for the engine and turbocharger to function at the higher load and thus higher mass flow rate the turbocharger has to increase its rotational speed and the surface temperatures have to settle at a new thermodynamic state. Both of these processes take time and during this time the combustion process may have to proceed under less than optimum circumstances due to the low boost pressure.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , 48 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2009:01
Identifiers
URN: urn:nbn:se:kth:diva-9929OAI: oai:DiVA.org:kth-9929DiVA: diva2:159595
Presentation
2009-01-26, Rum M36, KTH, Brinellvägen 64, Stockholm, 14:00 (English)
Opponent
Supervisors
Available from: 2009-02-09 Created: 2009-02-09 Last updated: 2010-10-27Bibliographically approved
List of papers
1. Development of a Fuel Spray Impulse Measurement Device and Correlation with Time Resolved Mass Flow
Open this publication in new window or tab >>Development of a Fuel Spray Impulse Measurement Device and Correlation with Time Resolved Mass Flow
2009 (English)In:  SAE Technical Paper 2009-01-1880, SAE International , 2009Conference paper, Published paper (Refereed)
Abstract [en]

The fuel injection process plays an important role in the combustion and emission formation processes of the DI diesel engine. One important fuel spray characteristic is the spray impulse. The most commonly used method to measure fuel spray impulse is the impingement method where the fuel spray impinges perpendicularly on the surface of a force transducer. This work deals with the theoretical background of such measurements as well as with developing and testing some different impulse measurement setups. The measured impulse is compared to measurements of the instantaneous mass flow and theoretical flow calculations. When measuring the impulse by impingement on the transducer membrane a fuel temperature related measurement error was encountered. This problem was solved by gluing a strike plate to the transducer membrane. The plate shielded the membrane from direct contact with the fuel. Initially plates made out of aluminum were used, they were however found to be sensitive to erosion. After a number of injections a small pit was formed and this led to an overestimation of the impulse as the fuel more effectively was reflected back towards the direction where it came from. It is crucial for the accuracy of the method that the spent fuel exits the plate perpendicularly, if some of the fuel bounces back towards the direction where it comes from the spray impulse is overestimated. With a flat strike plate it is difficult to be sure that all the spent fuel exits the plate perpendicularly. Therefore a plate with a rotationally symmetrical curvature which allows a gradual and thus more controlled direction change was manufactured and evaluated. When the injection rate of an injector is characterized using a conventional rate tube a number of problems are caused by pressure fluctuations in the fuel volume inside the rate tube. The measurements are disturbed by superimposed fluctuations which are especially problematic when small post injections are to be evaluated. The post injection rate can be disturbed by fluctuations introduced by the main injection, such fluctuations does not occur with impulse measurements. The new impulse measurement device produces measurements with high precision in both rate shape and absolute value. Because of this it is well suited for injection rate evaluation and when a high precision value of fuel spray impulse is required, for instance when calculating nozzle flow loss factors. Flow calculations based on the instantaneous mass flow and the fuel spray impulse are made.

Place, publisher, year, edition, pages
SAE International, 2009
Series
SAE Technical Paper Series, ISSN 0148-7191 ; 2009-01-1880
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-25552 (URN)10.4271/2009-01-1880 (DOI)2-s2.0-84877490425 (Scopus ID)
Conference
SAE World Congress 2009, Powertrains, Fuels and Lubricants Meeting. Florence, Italy 2009-06-15
Note
QC 20101027. Tidigare titel: "“Development and Testing of Some Variants of a Fuel Spray Momentum Measurement Device".Available from: 2010-10-27 Created: 2010-10-27 Last updated: 2011-05-30Bibliographically approved
2. A Study of Hole Properties in Diesel Fuel Injection Nozzles and its Influence on Smoke Emissions
Open this publication in new window or tab >>A Study of Hole Properties in Diesel Fuel Injection Nozzles and its Influence on Smoke Emissions
2008 (English)In: Proceedings Conference on Thermo- and Fluid Dynamic Processes in Diesel Engines, 2008Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-25553 (URN)978-84-8363-313-7 (ISBN)
Conference
Thiesel 2008 Conference on Thermo- and Dynamic Processes in Diesel Engines,Conferences & symposia, Valencia, Spain
Note
QC 20101027Available from: 2010-10-27 Created: 2010-10-27 Last updated: 2011-05-30Bibliographically approved

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