Computational diagnostics of diesel spray end-of-injection combustion recession

Conference item

Diesel engines are efficient, reliable, and durable, making them a popular choice for ground transportation and heavy-duty applications. While emissions controls are challenging for diesel engines, strategies such as low-temperature combustion (LTC) strategies have been proven to reduce nitrogen oxides and particulate matter emissions that are common in diesel engines. However, these strategies can result in an increased fraction of the fuel spray being unburnt, leading to unburned hydrocarbon (UHC) emissions. Previous studies have indicated that end-of-injection (EOI) processes can support ignition near the nozzle, thereby consuming the UHCs after EOI. In particular, combustion recession is an EOI process where high-temperature ignition occurs between the nozzle and flame lift-off length, consuming UHCs in the process. Current literature suggests that combustion recession is likely attributed to auto-ignition rather than flame propagation. This is inferred through the analysis of the flame structures at different boundary conditions. However, previous studies have not presented a quantitative analysis of whether combustion recession is driven by auto-ignition or flame propagation. Chemical explosive mode analysis (CEMA) is a flame diagnostic tool based on the eigenanalysis for the chemical Jacobian to identify critical combustion events and has been used in various types of combustion setups, including LTC of diesel sprays. CEMA has been successfully used to determine flame features and is also able to identify the local propagation regimes within a flame which includes autoignition, deflagration, and extinction. Therefore, the objective of this study is to further the understanding of the combustion recession of diesel sprays through computational fluid dynamics (CFD) at LTC conditions where a customized CEMA is implemented to study the EOI combustion modes. The study involves large eddy simulations of a single-hole injection of n-dodecane in an Eulerian-Lagrangian framework performed in the CFD solver CONVERGE. The boundary conditions of the study are in the range of Engine Combustion Network’s “Spray A” conditions. At the baseline boundary conditions of “Spray A”, two chemical kinetic mechanisms are compared with experimental data. With the selected chemical mechanism, the custom implementation of CEMA is used to determine the flame features AEOI and the propagation regime of combustion recession to provide insight into the flame re-initiation mechanism. Through CEMA, it was determined that combustion recession is auto-ignition dominated: the reactive mixtures near the nozzle auto-ignite, and the ignited kernels develop through flame propagation. Lower ambient temperatures cannot support auto-ignition, which leads to the extinction of the flame near the nozzle.

Authors: Arguelles, FJ; Fagade, MD; Hus, SP; Fang, XH

• Publication status: Accepted
• Peer review status: Peer reviewed
• Acceptance date: 2024-05-01
• Event title: Combustion Institute – Canadian Section 2024 Spring Technical Meeting
• Event location: Kingston, Ontario
• Event website: https://www.combustion-institute.ca/2024-meeting/
• Event start date: 2024-05-13
• Event end date: 2024-05-16
• Language: English