Modified Megatech Mark III EngineThe high speed video records can obtained to analyze the scavenging processes in the motored engine using air as the working fluid. The images show the development of the scavenging processes and clearly indicate the scavenging jet structure, the tumble pattern and the location of re-circulation regions.
LDA and PIV technique was also used to measure the scavenging flow field.
The analyses allow us to judge the quality of the scavenging processes. The small changes in geometry of the ports could significantly affect the scavenging flow. Tumble should be considered to control the scavenging flow in order to avoid short-circuiting losses and create condition favorable to combustion for a poppet-valved two-stroke engine.
For a larger image, click on the picture.
ENGINE SYSTEM
A four-stroke engine with a transparent cylinder (Megatech Mark III, made by Megatech Corporation, which can be fired) was modified, by changing the cam shaft and the timing gears, into a poppet-valved two-stroke engine for this investigation. The cooling system, carburetor, muffler and ignition system of the engine have been removed since only motored condition was required in the experiment.
Modified Megatech Mark III Engine
VISUALIZATION
The images were recorded by a high speed video camera (Type HS4540, KODAK EKTAPRO HS Motion Analyzer) with framing rate of 4500 frames per second and an aperture setting of F1.8. A laser sheet of 1mm in depth and a power of 2 W (Ar+ gas laser, NEC 3200) was made by a cylinderic lens with f=7 mm and located on the cylinder axis. The in-cylinder flow was observed using vertical laser sheet illumination in two directions of X and Y, the X was through the center-points of inlet-valve and outlet-valve, the Y was perpendicular to a line connecting the two valves. The laser sheet locations and camera viewing directions are shown in Figure 7. The vertical laser sheet enters from the left side of the images in case of X direction and from right side in Y direction. Only first cycle's scavenging flow, as well as the light of two diodes which flashed every 10 degree of crank angle and BDC respectively to time the images, was recorded.
Photograph of experiment setup of visualization
LDA measurement
Laser Doppler Anemometer (DISA Mark II of a differential forward scattering type) was used to measure the axial mean velocities in the cylinder. The total angle of intersecting beams was 7.74 degree. Silicone oil mist (diameter 2 to 3 micrometer) was used as seeding particle which was supplied to the fog tank, which maintained its pressure at 26.3 kPa same as the case of the visualization experiments. Motored rotation speed was continuously 750 r/min other than 500 r/min for one cycle test. The measuring points including 30 points, where the measuring plane was located on the cylinder axis and through the center-points of inlet-valve and exhaust-valve, i.e. in X direction as mentioned above.
PIV measurement
The DANTEC Particle Image Velocimetry system was used. The illumination system is composed of a Generic aron-ion laser and cylinderical lenses (80*20 light sheet optics). Visualisation videos of the flow can be recorded with a camera (canera: 80C42 Double Image 700 Camera, camera shutters: 80C40 Flow Sense, camera lenses: Micro-Nikkon 60mm). The laser can be pulsed using a electro-optical shutter (80*41 Electro-optical Shutter) synchronised with the video output of the camera. The PIV processing is performed with the FlowMap PIV2000 Processor. The location of the laser sheet is same as in LDA measurement. Time between pulses is 100 microsecond and the duration of one pulse is 0.006 microsecond.
Photograph of experiment setup of PIV measurement
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