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Optical Research Engines-Tools in Gasoline Engine Development?
Published March 22, 1994 by Institution of Mechanical Engineers in United Kingdom
Numerous research engines have been designed to allow the optical investigation of in-cylinder fluid flow and combustion phenomena. Their design concepts are usually matched to the requirements of the optical techniques applied in the actual studies, and thus, machines have resulted which quite often have a rather limited scope of application.
However, the amount of information to be gained from diagnostic techniques such as LDA, PIV, CARS, LIF, combustion photography etc., created interest in applying such techniques in the development process of combustion systems. As combustion system engineering aims at supporting and governing flame propagation by means of in-cylinder fluid dynamics and turbulence generation and by the preparation and distribution of the fuel-air mixture, there is considerable interest to visually "see" the influence of hardware or process variations on flow field, on mixture distribution and on flame propagation.
On the one hand this creates the need for an optical engine concept which allows:
1. a wide range of operating conditions for engine speed and load
2. the variation of hardware components, e.g. the attachment of different cylinder heads to an optical base engine, and
3. which provides access to the combustion chamber necessary for the straightforward application of the diagnostic techniques.
On the other hand, engine development requires data which provide fast and specific insight into the phenomena of interest and which are sensitive enough to demonstrate the variations introduced in the different steps of hardware or process design.
The paper describes the design of a singe cylinder base engine which provides optical access to the combustion chamber via glass cylinders and a piston with a glass crown.
The application of this engine to the visual analysis of gasoline mixture formation and combustion is demonstrated with examples given for two- and four-valve cylinder heads.
The optical methods used in this study comprise of Laser-induced Florescence (LIF) to image the unburned mixture within the laser light sheet illuminating a plane of the combustion chamber and of flame photography to visualize flame propagation. Simultaneous recording of engine thermodynamic data allows to compare conventional engine diagnostics with the results gained from the optical techniques.