Combustion Modeling Lab at UC Berkeley

Current Research

Laminar flame speeds of stratified mixtures

Xian Shi, Daniel Pineda (CML)


Fuel-stratified, overall-lean combustion has become one of the potential internal combustion engine techniques. While lean combustion leads to low NOx emission without losing combustion efficiency, fuel stratification improves ignitability and flame stability. In addition, fuel stratification is also regarded as a useful technique to control combustion phasing and expand load limits in piston engines. Despite its wide application in industries, fundamental understanding of stratified flames is still incomplete, which impedes the development of advanced direct fuel injection control strategies. When the stratified mixture is ignited, a consequent flame will be established and propagate through the stratified mixture. How fast the stratified flame propagates compared to the corresponding homogeneous flames is a key question to answer as to the determination of combustion duration and emissions. However, the difference between laminar flame speeds of stratified and homogeneous flames is still neither well understood nor quantified. The objectives of this project are:

1) Understand how stratified flame behaves differently in comparison to homogeneous flames, both qualitatively and quantitatively.

2) Develop a prediction model for laminar flame speeds of stratified mixtures.

Both numerical and experimental investigations are conducted: Numerically, an 1-D compressible reacting flow solver ASURF-Parallel is used to simulate both stratified flames and homogeneous flames. A typical stratified flame setup is given below. Experimentally, soap bubble experiments are conducted in a constant-volume chamber with two different mixtures filled inside and outside the bubble. A stratified mixture and then corresponding flame can be formed when the mixture inside the bubble is ignited and propagates towards the outside mixture.

Related papers

X. Shi, J.Y. Chen, Y. Chen, Laminar Flame Speeds of Stratified Methane, Propane, and n-Heptane Flames, Combust. Flame 176 (2017) 38-47.

X. Shi, J.Y. Chen, Z. Chen, Numerical study of laminar flame speed of fuel-stratified hydrogen/air flames, Combust. Flame 163 (2016) 394-405.

Stratified shcematicSchematic of stratified flame setup in 1-D planar coordinate