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Characteristics of Heat Release History of Multi-Hole Diesel Spray Affected by Initial Mixture Formation, Wall Impingement and Spray Interaction
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
Spray development and mixture formation are important process for initial diesel combustion. Moreover, wall impingement of spray and spray interaction of multi-hole spray also affect combustion process greatly. This study investigated influence of spray combustion with both wall impingement and spray interaction on heat release history. The experiment observed initial spray development by shadowgraph technique using a constant volume spray chamber. The injectors were single-hole and 8-hole injectors with the same hole-diameter. Further, 6-hole and 4-hole injectors with different hole-diameters were used for reference. The combustion experiment carried out to observe flame development caused by spray combustion. The spatial distribution of the flame temperature and soot were analyzed by the flame images. The unburned and burned spray images can explain the difference of mixture formation and initial combustion between single-hole and multi-hole sprays. Single-hole spray tends to form air-fuel mixture mainly in the downstream region of spray and rich mixture is formed at center in upstream region. In contrast, multi-hole spray tends to extent in midstream region as well as downstream region at initial stage of injection, and at end of injection, the spray spreads widely in the case of multi-hole spray. During spray combustion, low flame temperature region is formed by wall-impingement. As for the multi-hole spray, the spray interaction after wall-impingement also forms low temperature flame area in the interference region. Heat release rate caused by the spray combustion is controlled by the spray interaction of multi-hole spray. Soon after the interaction, spray combustion is progressed in the whole spray chamber, which increases the heat release rate again and decreases soot concentration. The influence of spray interaction on flame temperature distribution and heat release rate history appears more clearly with 8-hole spray rather than with 6-hole spray, where 8-hole spray has shorter distance of neighboring spray.