Numerical Study on the Combustion Process of n-heptane Spray Flame in Methane Environment Using Large Eddy Simulation

ABSTRACT

Large eddy simulation is applied for the combustion process of n-heptane spray flame in methane environment. The influence of methane (CH₄) concentration on the auto-ignition process and flame structures are discussed in detail. By increasing the CH₄ concentration in the ambient gas, auto-ignition is delayed obviously at a low initial temperature because of the delayed first-stage ignition. While at a high temperature, the auto-ignition time is less influenced by the addition of CH₄. However, after the addition of CH₄, the concentration of the mixture where the high-temperature ignition is initialed becomes much richer and it is independent of the initial temperatures. In addition, the chemical explosive mode analysis (CEMA) method shows that the mixture in high-temperature regions is non-explosive without CH₄ addition, and the abrupt transition between the explosive and non-explosive mixture at the tip of the reacting spray is observed by adding CH₄ in the ambient gas, indicating that a flame front is developing downstream. This flame front exists for a long time at low CH₄ concentration. The eigenvalue of the Jacobian matrix for the CH₄/air mixture in the ambient gas is increased significantly with the addition of CH₄, indicating that the combustion process is dominated by auto-ignition. Finally, results show that the development of the flame is accelerated by the addition of CH₄ in the ambient gas.

KEYWORDS:

• Chemical explosive mode analysis
• dual-fuel combustion
• ignition
• low-temperature combustion

Disclosure statement

We declare that we have no conflict of interest.

Additional information

Funding

The work is supported by National Natural Science Foundation of China (Grant No. 91741119, 51606133, 91641203) and Marine Low-Speed Engine Project (Phase I). The work was carried out at National Supercomputer Center in Tianjin, and the calculations were performed on TianHe-1 (A).