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On discharge from poppet valves: effects of pressure and system dynamics
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
2018 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, no 2, article id 24Article in journal (Refereed) Published
Abstract [en]

Simplified flow models are commonly used to design and optimize internal combustion engine systems. The exhaust valves and ports are modelled as straight pipe flows with a corresponding discharge coefficient. The discharge coefficient is usually determined from steady-flow experiments at low pressure ratios and at fixed valve lifts. The inherent assumptions are that the flow through the valve is insensitive to the pressure ratio and may be considered as quasi-steady. The present study challenges these two assumptions through experiments at varying pressure ratios and by comparing measurements of the discharge coefficient obtained under steady and dynamic conditions. Steady flow experiments were performed in a flow bench, whereas the dynamic measurements were performed on a pressurized, 2 l, fixed volume cylinder with one or two moving valves. In the latter experiments an initial pressure (in the range 300–500 kPa) was established whereafter the valve(s) was opened with a lift profile corresponding to different equivalent engine speeds (in the range 800–1350 rpm). The experiments were only concerned with the blowdown phase, i.e. the initial part of the exhaustion process since no piston was simulated. The results show that the process is neither pressure-ratio independent nor quasi-steady. A measure of the “steadiness” has been defined, relating the relative change in the open flow area of the valve to the relative change of flow conditions in the cylinder, a measure that indicates if the process can be regarded as quasi-steady or not.

Place, publisher, year, edition, pages
Springer, 2018. Vol. 59, no 2, article id 24
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-222028DOI: 10.1007/s00348-017-2478-8ISI: 000424707100001Scopus ID: 2-s2.0-85040812357OAI: oai:DiVA.org:kth-222028DiVA, id: diva2:1178903
Funder
Swedish Energy Agency
Note

QC 20180131

Available from: 2018-01-31 Created: 2018-01-31 Last updated: 2019-04-23Bibliographically approved
In thesis
1. Dynamics of Exhaust Valve Flows and Confined Bluff Body Vortex Shedding
Open this publication in new window or tab >>Dynamics of Exhaust Valve Flows and Confined Bluff Body Vortex Shedding
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Dynamik för avgasventilflöden och virvelavlösning från trubbiga kroppar
Abstract [en]

This thesis can be divided into two interconnected topics; engine exhaust-valve flows and confined bluff-body vortex shedding. When optimising engine flow systems it is common to use low order simulation tools that require empirical inputs, for instance with respect to flow losses across the exhaust valves. These are typically obtained from experiments at low pressure ratios and for steady flow, assuming the flow to be insensitive to the pressure ratio and that it can be considered as quasi-steady. Here these two assumptions are challenged by comparing measurements of mass-flow rates under steady and dynamic conditions at realistic pressure ratios. The experiments with a static valve were carried out using a high-pressure flow bench at cylinder pressures up to 500 kPa. For the dynamic-valve experiments the transient flow rate during the blowdown phase of an initially pressurised cylinder was determined. Here a linear motor actuated the valve to obtain equivalent engine speeds in the range 800–1350 rpm. It was shown that neither of the above mentioned assumptions are valid and a new non-dimensional quantification of the steadiness of the process was formulated. Furthermore it was shown through Schlieren visualisation that the shock structures in the exhaust port differ depending on if the system dynamics are included or not. The study shows that reliable results of flow losses past exhaust valves can only be obtained in dynamic experiments at representative pressure ratios. The second topic arose from the need to monitor time-resolved mass-flow rates in conduits. A mass-flow meter based on vortex shedding from bluff bodies was designed where microphones are used to detect the shedding frequency. It consists of a forebody and a downstream mounted tail and the system was shown to be capable of measuring pulsating flow rates. Furthermore, the flow topology associated with different forebody and splitter plates has been characterised, through visualisation of the flow behind the shedder and on the splitter plate. It has been shown that for long splitter plates a “horse shoe” like vortex, which attaches to the tail, is formed. It has also been shown that another energetic mode (denoted mode-II) can interact with and disrupt the primary vortex formation. A hypothesis for the appearance of mode-II has been formulated, linking it to the periodic separation of the boundary layer at the conduit wall.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 77
Series
TRITA-MEK, ISSN 0348-467X ; 2019:16
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-249702 (URN)978-91-7873-159-6 (ISBN)
Public defence
2019-05-24, F3, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20190423

Available from: 2019-04-23 Created: 2019-04-17 Last updated: 2019-04-23Bibliographically approved

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