A dynamical instability of spark-ignited engines

Area of Science:

• Thermodynamics
• Combustion Science
• Engine Dynamics

Background:

• Spark-ignited engines are susceptible to performance variations due to complex combustion phenomena.
• Cyclic dispersion, a known issue in internal combustion engines, leads to inconsistent power output.
• Understanding the root causes of cyclic dispersion is crucial for engine efficiency and emissions control.

Purpose of the Study:

• To develop a simplified model for spark-ignited engines.
• To investigate the role of residual exhaust gases in ignition processes.
• To elucidate the mechanisms behind cyclic dispersion in engines.

Main Methods:

• A one-dimensional, discrete, nonlinear mapping model was developed.
• Laminar flame correlations with Arrhenius kinetics were incorporated for ignition modeling.
• The model analyzed the impact of ignition timing variations on work output and exhaust gas temperature.

Main Results:

• Mixing of hot residual gases with a fresh charge was identified as a key factor causing ignition instability.
• This instability leads to oscillatory behavior in the combustion process.
• The model demonstrates how compounded effects of residual gas mixing and mixture turbulence explain cyclic dispersion.

Conclusions:

• The proposed model provides a novel explanation for cyclic dispersion in spark-ignited engines.
• Residual exhaust gas dynamics are a critical determinant of ignition stability.
• The findings offer insights into controlling engine performance variability.