Influences of the internal residual on combustion instabilities in the misfire and partial burn regimes of a dilute spark-ignition engine

<p>"Dilution in spark-ignition (SI) engines can improve fuel consumption and reduce emissions; however, increased levels of dilution either from excess oxidizer or exhaust gas recirculation (EGR) causes combustion to become more strained and cycle-to-cycle variations increase. At high levels of dilution incomplete combustion events (i.e. misfires and partial burns) start to occur, which cause combustion instabilities and eventually a dilute limit is reached. It is known the combustion instabilities seen are primarily due to the feed-forward mechanism present in the residual gases, but it is still unknown what about the residual is influencing the dynamics under high levels of dilution at different dilute limits. Understanding the influence different effects of the residual have on the dynamics is necessary in applying effective control methods at different dilute limits. The residual varies in both quantity and composition from cycle-to-cycle and is likely different between misfires and partial burns. This study focuses on how three different effects of the residual impact the dynamics in both the misfire and partial burn regime. Namely, the dilution effect, the heat capacity effect (i.e. thermal effect) and chemical kinetic effect. Each effect was isolated by modifying the composition of the residual using different species. Species used in this study included excess air, nitrogen (N₂), and carbon monoxide (CO).</p> <p>The different residual effects were investigated both experimentally and numerically. First, experiments on a single-cylinder research engine were conducted to isolate the three different effects using different combinations of the mentioned species. Results showed the dynamics between the misfire and partial burn regime are different and the misfire regime is more sensitive to the chemical kinetic effect. Second, a multi-cycle turbulent combustion model that accounts for both chemical and mixing times along with residual effects was used to see if the complex dynamics seen experimentally could be captured. Results showed the model was capable of capturing differences between regimes, but was unable to capture the complexity of the dynamics seen experimentally, particularly in the partial burn regime"--Abstract, p. iii</p>

Name thesis:degree_name

Ph. D. in Mechanical Engineering

Grantor

Missouri University of Science and Technology

Author dc:creator

• Stiffler, Rachel Inez

• combustion
• cyclic variability
• dilute combustion
• internal residual
• misfires and partial burns
• spark-ignition engine
• Engineering
• Mechanical Engineering

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/3233

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-4238