Evaluation of fuel spray ignition delay behavior using a two-stage Lagrangian model

Yu Wang (Corresponding author), Hesheng Bao (Corresponding author), Bart Somers, Noud Maes (Corresponding author)

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Abstract

In this study, a two-stage Lagrangian (TSL) model is used to investigate the ignition process of a fuel spray under engine-like conditions. The existing two-reactor TSL model developed for quasi-steady flames is improved to simulate the ignition process of a fuel spray at engine-like conditions, by inserting a well-validated entrainment model for the liquid fuel spray. The ignition delays of n-dodecane and n-heptane sprays predicted by the improved TSL model are validated with Engine Combustion Network Spray A and Spray H data over a wide range of ambient temperatures and oxygen concentrations. The results show that the two-reactor TSL model is capable of capturing the complex interaction between turbulent mixing and chemistry at the spray core and periphery regions during ignition. A 4-step ignition process at intermediate temperatures is observed. First, 1st-stage ignition appears at the fuel-lean spray periphery when the local residence time reaches a critical value. Then, the transport prompts the 1st-stage ignition in the core region. After a kinetic-dominated 2nd-stage ignition in the fuel-rich core region, the flame propagates into the whole equivalence ratio space. At ambient temperatures that are considered relatively high for internal combustion engines, the 1st-stage and 2nd-stage ignition in the fuel-rich core region is so short that the 1st-stage ignition does not occur at the spray periphery, resulting in a 3-step ignition process. The high equivalence ratio in core region restricts the local temperature rise, and the 2nd-stage ignition finally appears at the spray periphery with an increasing local residence time and the transport from the core region. The effectiveness of the two-reactor TSL model also demonstrates the dominant role of transport in the multiple-step ignition process of a high-pressure liquid fuel spray. The ignition process of high-pressure liquid fuel sprays is of great interest in engine combustion research, but the simulation of this process is computationally costly. In this study, a reduced order, two-stage Lagrangian (TSL) model, is extended to ignition process simulations. Based on the configuration of two perfectly stirred reactors with a well-developed 1-D fuel spray entrainment sub-model, the TSL model is able to accommodate detailed chemical kinetic mechanisms. Validated by ECN Spray A and Spray H data, this model provides good predictions of ignition delay for fuel sprays at engine-like conditions. Moreover, this model explains the roles of transport and chemistry at the spray periphery and core regions during the multiple-step ignition process. The model developed in this study helps the understanding of the multiple-step ignition process, and it can also be of great significance in chemical mechanism development and validation.

Original languageEnglish
Article number113449
Number of pages11
JournalCombustion and Flame
Volume265
DOIs
Publication statusPublished - Jul 2024

Funding

This research is supported by the European Union's Horizon 2020 Research and Innovation programme (SmartCHP project, Grant Agreement No. 815259).

FundersFunder number
Horizon 2020 Framework Programme815259

    Keywords

    • Engine Combustion Network Spray A & H
    • Ignition delay
    • Ignition process
    • Spray combustion
    • Two-stage Lagrangian (TSL) model

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