Droplet vaporization and combustion in engines

Understanding the phenomena involved, and knowing how to calculate the evolution of a single drop or a group of drops to better predict engine performance, is a goal that remains relevant today. First of all, it's best to ensure that evaporation and combustion take place inside the engine, and not in the exhaust pipe (explosion engines) or in the nozzle (rocket engines using liquid propellants, for example). It's worth remembering, for example, that an initial calculation of the size of a rocket engine is based on an estimate of the length required for complete combustion of a drop of fuel injected at the combustion chamber inlet. Improving combustion efficiency to obtain higher yields and developing less polluting engines are current and future motivations for research in this field. These reminders show the vital importance of the subject tackled through some of the problems posed by evaporation and droplet combustion.

In this article, the paragraph 1 is devoted to the generation of drops, whether natural (dew) or artificial (engine injection, sprays). The formation of sprays by destabilization of flat, cylindrical or conical liquid sheets is studied. Particular emphasis is placed on diesel engines. Droplet size distribution is determined using the maximum entropy method applied to thin slicks. This method reaches its limits when we want to study the atomization of thick jets, as is the case in cryogenic rocket engines. Another method is to study droplet formation from ligaments.

Paragraph 2 is devoted to the combustion of a single drop, with various simplifying assumptions, including the absence of interaction with its neighbors. The famous "d ² law" is presented, along with cases where it is no...