Characteristics of Heat Release History of Multi-Hole Diesel Spray Affected by Initial Mixture Formation, Wall Impingement and Spray Interaction

Spray development and fuel-air mixture formation are important process early in diesel combustion. Moreover, wall impingement of spray and spray interaction also affect combustion process greatly. The spray interaction happens in multi-hole injector. This study investigated influence of spray combustion accompanied with 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 a single-hole injector and multi-hole injectors with the hole-number of 8, 6 and 4. The combustion experiment observed flame development. The spatial distribution of the flame temperature and the soot oxidation were analyzed by the flame images. Results of the unburned spray images revealed 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 the center in upstream region. In contrast, multi-hole spray distributes fuel in midstream region as well as downstream region at the initial stage of injection, and at the end of injection, the spray spreads widely in the case of multi-hole spray. Images of spray combustion of multi-hole spray showed that the spray interaction after wall-impingement forms low temperature flame area and restrains soot oxidation in the interference region. Heat release rate caused by the spray combustion is controlled by the spray interaction of multi-hole spray. The influence of spray interaction appears more clearly with 8-hole spray rather than with 6-hole spray.