No abstract

The partial replacement of diesel fuel with gaseous fuels in diesel engines allows for reducing soot, increasing the renewable fraction of the fuel and decreasing CO 2 emissions. Hydrogen is a promising alternative; since it is a non-carbon compound, it can be produced from renewable sources and it has suitable combustion properties. However, the use of hydrogen in diesel engines could require some modifications on the engine calibration. Among the different phenomena involved in diesel combustion, autoignition significantly affects the engine efficiency. This work analyzes the autoignition behavior of diesel and biodiesel fuels under a H 2-rich ambient. Two different liquid fuel replacements (10% and 20% by energy) have been tested in a constant-volume combustion chamber. Three different chamber temperatures (535°C, 602°C, and 650°C) and equivalence ratios (0.4, 0.6, and 0.8) have been checked. Results show that, in the case of diesel fuel, hydrogen delays autoignition and reduces the combustion rate, the latter caused by a higher fuel dilution with air. The influence of H 2 in the autoignition of biodiesel is less significant. A reduction in the OH radicals pool appears as the main reason for retarding ignition. The lower pressure peaks with hydrogen suggest unburnt hydrogen to be relevant.

Numerical simulations of simplex pressure-swirl atomizers can aid their design process toward better atomization. This work aims at studying the two-phase flow at both the internal geometry and the first millimeters of the external domain of such atomizers, where primary breakup takes place. In particular, the atomizer under study has been used in the CORIA Rouen Spray Burner (CRSB) test rig, which aims at studying lean premixed turbulent combustion. Ultimately, our goal is to complete the spray characterization in the vicinity of the injector. Such data will potentially enforce the validity of numerical simulations of nonreacting and reacting flow for this burner. Injection characteristics are analyzed through an interface capturing method within a detailed numerical simulations framework. The importance of the internal flow simulation on the final result is demonstrated in the manuscript, but it requires accurately measuring the injector internal geometry. In the present investigation, an experimental methodology combining different techniques is applied to this end, obtaining and parameterizing the actual geometry of the internal ducts within the atomizer. The numerical workflow is divided in two simulations to separately study the internal flow formation and the external spray development. This division is proposed given the difficulty to mesh the whole computational domain handling all the present length scales while still preserving the required accuracy. Several mesh refinements are studied for each simulation, also analyzing the coupling between the related internal and external simulations. The methodology is validated against experimental data for two CRSB operating conditions. The investigation then proves it is possible to couple the internal and external flow in order to describe the actual air core formation, liquid film behavior and breakup mechanism of these atomizers, extracting relevant atomization outputs in the near-field region where experimental data are scarce.