Studies of the Combustion Process with Simultaneous OH- and Formaldehyde-PLIF in a Direct-Injected HCCI engine
Författare
Summary, in English
This paper presents simultaneous laser based measurements of formaldehyde and OH-radical distributions in an HCCI engine. Formaldehyde is formed as an intermediate species when combusting hydrocarbons. The formation occurs through low temperature reactions in an early phase of the combustion process. Later in the process formaldehyde is being consumed. Formaldehyde is, therefore, used as indicator of the first stage of combustion and a marker of zones with low-temperature reactions. The OH radical is formed as an intermediate during the high temperature reactions, and is used as a marker of zones where the combustion is ongoing. The purpose of the investigation was to study how the combustion process is affected by the change in homogeneity that arises from early and late injection, respectively.
A 0.5 liter single-cylinder optical engine equipped with a DI common rail fuel system was operated with a number of different injection timings, resulting in various levels of charge stratification. A blend of iso-octane and n-heptane was used as fuel. The measurement technique used was planar laser-induced fluorescence where formaldehyde was excited at 355nm and OH at 283nm. Two separate ICCD units were used to detect the resulting fluorescence from formaldehyde and OH. Measurement series covering the process from the start of injection until late in the expansion stroke is presented for different injection timings as well as pressure traces and emission analysis. A homogeneity index is calculated and used to compare the level of homogeneity resulting from injection timings. From early injection until about 50CAD BTDC the time, between onset of low temperature reactions and start of the high temperature reactions, is long enough for the formaldehyde to form an almost homogeneous distribution before it is being consumed. For later injection timings the high temperature reactions starts before this mixing is completed and therefore the formaldehyde distribution is not longer homogeneous and the combustion is more diesel like.
Avdelning/ar
Publiceringsår
2004
Språk
Engelska
Sidor
311-317
Publikation/Tidskrift/Serie
[Host publication title missing]
Dokumenttyp
Konferensbidrag
Förlag
Japan Society of Mechanical Engineers
Ämne
- Other Mechanical Engineering
- Atom and Molecular Physics and Optics
Nyckelord
- HCCI
- Direct-Injection
- Formaldehyde
- OH
- PLIF
Conference name
Sixth International Symposium on Diagnostics and Modeling of Combustion in Internal Combustion Engines
Conference date
2004-08-02 - 2004-08-05
Conference place
Yokohama, Japan
Status
Published