Vaporisation characteristics of methanol, ethanol and heptane droplets in opposed stagnation flow at low temperature and pressure

Abstract

A computational model is developed and applied to study the vaporisation behaviour of three liquid fuels. This fundamental study is motivated by a need to understand how the performance of direct-injection-spark-ignition (DISI) engines may be affected by changes in fuel composition, especially alcohols. Currently, most DISI engines are designed for homogeneous-charge combustion, where the in-cylinder fuel injection, vaporisation and mixing is accomplished during the intake and early in the compression process. Thus the temperature and pressure are low, compared to post-compression conditions. The two-phase axisymmetric model is based upon an ideal opposed stagnation flow field. Liquid droplets are carried in one air stream that is met by an opposed air flow. Because of stagnation-flow similarity, the mathematical model can be represented as a one-dimensional boundary-value problem. Results show significant differences between methanol, ethanol and heptane fuels, which have potentially important impacts on the design and modification of fuel-injection systems for direct-injection engines with alternative fuels.

Keywords:

• liquid fuel droplets
• opposed stagnation flow
• computational modelling
• droplet vaporisation
• two-phase flow

Acknowledgments

[Acknowledgements]

This research was initiated during a six-week visit by RJK and HZ to the Automotive Research Institute of Shanghai Jiao Tong University, and is supported by General Motors. We gratefully acknowledge the assistance of Dr Steven DeCaluwe (NIST) in evaluating ethanol properties. The Colorado School of Mines’ effort was supported by the Office of Naval Research via grant N00014-08-1-0539.