Experimental and Modeling Study of Wall Film Effect on Combustion Characteristics of Premixed Flame in a Constant Volume Combustion Bomb

Shijie Bai,Xingyu Liang,Hongsheng Zhang,Chaohui Wu,Chang Li,Kun Wang

doi:10.3389/fmech.2021.743342

Abstract

The primary objective of the present study was to investigate the impact of wall film on the combustion characteristics of premixed flames in internal combustion engines through the joint experimental and numerical techniques. The interaction between the premixed methane-air flame and n-dodecane film attached to the wall of a constant volume combustion bomb was experimentally examined. The flame propagation processes, as well as pressure evolution were quantitatively characterized. Then, computational fluid dynamic (CFD) simulation was performed incorporating the combustion chemistry model. To enable efficient simulation of the chemically reacting flow in engine chambers, a simplified modeling approach based on a two-step reaction scheme was developed. A compact reaction model for the selected model fuel n-dodecane was constructed and reduced to include 35 chemical species and 180 reactions. The flame propagation process of the premixed flame and its interaction with dry and wet walls was studied. The results showed that the propagation of the premixed flame could be divided into four stages, and the existence of the slit structure increased the instability of the flame structure in the near-wall region. The wall film tended to promote emissions, producing more unburned hydrocarbons, soot precursors and aldehydes.

Highlights

Direct injection engines are rapidly dominating the engine market due to the higher compression ratio, increased thermal efficiency and fuel economy
A two-step method was developed to obtain a kinetic model for the methane and n-dodecane combustion reactions, which was reduced and validated
The effect of the wall film in the constant volume combustion bomb on the methane flame propagation process was investigated by a threedimensional model numerical calculation

Summary

Introduction

Direct injection engines are rapidly dominating the engine market due to the higher compression ratio, increased thermal efficiency and fuel economy. For small and medium-sized high-speed direct injection diesel engines, the fuel spray is likely to collide with the wall of the combustion chamber to form a wall-mounted film due to the limitation of the combustion chamber geometry (Brandriss et al, 1998; Zhao et al, 1999; Shim et al, 2009; Zhang et al, 2016). In order to further reduce emissions and improve fuel efficiency, early injection technology has been widely used, through which injection strategy, part of the fuel is injected into the cylinder early in the compression stroke. At this moment, the temperature and pressure inside the cylinder are relatively low and the evaporation rate slows down, which increases the spray penetration distance in the cylinder chamber.

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Conclusion