| 1. |
- Persson, Håkan, et al.
(författare)
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Investigation of Boundary Layer Behavior in Hcci Combustion Using Chemiluminescence Imaging
- 2005
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Ingår i: SAE, Session: Homogeneous Charge Compression Ignition (HCCI) (Part 6 of 6). - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. ; 114:4, s. 1358-1369
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Konferensbidrag (refereegranskat)abstract
- A five-cylinder diesel engine, converted to a single cylinder operated optical engine is run in Homogeneous Charge Compression Ignition (HCCI) mode. A blend of iso-octane and n-heptane is used as fuel. An experimental study of the horizontal boundary layer between the main combustion and the non-reacting surface of the combustion chamber is conducted as a function of speed, load, swirl and injection strategy. The combustion behaviour is monitored by chemiluminescence measurements. For all cases an interval from -10 to 16 crank angles after top dead center (CAD ATDC) in steps of one CAD are studied. One image-intensified camera observes the boundary layer up close from the side through a quartz cylinder liner while a second camera has a more global view from below to see more large scale structure of the combustion. The averaged chemiluminescence intensity from the HCCI combustion is seen to scale well with the rate of heat release. A boundary layer is defined and studied in detail between the main combustion volume and the piston crown surface as a function of crank angle. The boundary layer is found to be in the range from 2 to 4 mm for all cases by the definition used; however, the location for the measurements becomes more and more important as combustion becomes more inhomogeneous. To get accurate calculations, the level of noise must also be considered and definitions of boundary layer thickness should not be made at to low chemiluminescence intensity.
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| 2. |
- Persson, Håkan, et al.
(författare)
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Investigation of the Early Flame Development in Spark Assisted HCCI Combustion Using High Speed Chemiluminescence Imaging
- 2007
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Ingår i: SAE, Session: Homogeneous Charge Compression Ignition (HCCI) (Part 5 of 8) Optical Diagnostics. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Konferensbidrag (refereegranskat)abstract
- Auto-ignition with SI-compression ratio can be achieved by replacing some of the fresh charge by hot residuals. In this work an engine is run with a negative valve overlap (NVO) trapping hot residuals. By increasing the NVO, thus raising the initial charge temperature it is possible to investigate the intermediate zone between SI and HCCI as the amount of residuals is increased. Recent research has shown the potential of using spark assistance to aid gasoline HCCI combustion at some operating conditions, and even extend the operating regime into regions where unsupported HCCI combustion is impossible. In this work the influence of the spark is studied in a single cylinder operated engine with optical access. Combustion is monitored by in-cylinder pressure and simultaneous high speed chemiluminescence imaging. It is seen that even for large NVO and thus high residual fractions it is a growing SI flame that interacts with, and governs the subsequent HCCI combustion. Using the spark timing it is possible to phase the combustion timing even when the major part of the released heat is from HCCI combustion. The flame expansion speed is decreases for higher NVO, but prevails also for high residual fractions. A higher spark advance is found to compensate for the slower flame expansion up to a point. The auto-ignition process is found to be stratified for both spark assisted HCCI as well as for pure HCCI. For pure HCCI the initial front spreading velocity is found to be in the same order of magnitude as for the expansion speed of the SI flame. Calculations to estimate the crank angle of auto-ignition are performed based on cylinder pressure information providing good statistics on how the proportion of SI to HCCI behaves for different operating conditions.
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