An experimental study of the detailed flame transport in a SI engine using simultaneous dual-plane OH-LIF and stereoscopic PIV

TL;DR

This study provides detailed experimental measurements of flame transport in spark-ignition engines using advanced optical techniques, revealing complex flame/flow interactions and aiding the development of more accurate engine combustion models.

Contribution

It introduces a comprehensive dataset of 3D flame and flow dynamics in SI engines, combining dual-plane OH-LIF and stereoscopic PIV to improve understanding of flame transport mechanisms.

Findings

Flame displacement speed correlates inversely with flame curvature.

Higher RPM increases flame wrinkling and broadens displacement speed distribution.

Spatial distributions of gas velocity and flame speed identify dominant transport mechanisms.

Abstract

Understanding the detailed flame transport in IC engines is important to predict ignition, rate of heat release and assess engine performance. This is particularly important for RANS and LES engine simulations, which often struggle to accurately predict flame propagation and heat release without first adjusting model parameters. Detailed measurements of flame transport are required to guide model development. This work introduces an experimental dataset designed to study the detailed flame transport and flame/flow dynamics for SI engines. Simultaneous dual-plane OH-LIF and stereoscopic PIV is used to acquire 3D measurements of unburnt gas velocity, flame displacement speed and overall flame velocity during the early flame development. Experiments are performed in an optical engine operating at 800 and 1500 RPM with premixed C8H18-air mixtures. Analysis reveals several distinctive flame/flow configurations that yield a positive or negative flame displacement for which the flame progresses towards the reactants or products, respectively. For the operating conditions utilized, Sd exhibits and inverse relationship with flame curvature; a strong correlation between negative Sd and convex flame contours is observed. Trends are consistent with thermo-diffusive flames, but have not been quantified in IC engines. Flame wrinkling is more severe at the higher RPM, which broadens Sd distribution towards higher positive and negative velocities. Spatially-resolved distributions of Ugas and Sd describe in-cylinder locations where convection or thermal diffusion is the dominating mechanism contributing to flame transport. Findings are discussed in relation to common engine flow features, including flame transport near solid surfaces. Findings are designed to support engine simulation validations.