Low temperature oxidation of diesel–air mixtures at atmospheric pressure

Abstract

Low temperature oxidation processes of diesel–air mixtures have been examined in a temperature range between T = 590 and 830 K for air ratios from λ = 0.1 to 1.2. The experiments were conducted in a flow reactor, where vaporized diesel fuel and air were merged in a specially designed mixing unit. In doing so the influence of physical processes like evaporation and mixing have been minimized and the chemical properties of the mixture are dominant. In the investigated parameter field, several regimes with different types of reaction can be identified by determining the heat release rate inside the reactor. The initiation of oxidation reactions in the mixture starts between T = 600 and 610 K. In the temperature range between T = 620 and 740 K cool flame reactions with a negative temperature coefficient are dominant. At higher temperatures slow oxidation reactions with lower heat release rates were observed. It is these reactions that lead the system to thermal explosion. The experimental results are used to determine design criteria for evaporators used in liquid fuel premix systems like burners, HCCI-engines and reformers for fuel cell applications. Thus undesirable auto ignitions are avoided and low temperature reactions such as cool flames can be stabilized in order to optimize the evaporation process.