Autoignitions and detonations in engines and ducts

Area of Science:

• Combustion Science
• Chemical Engineering
• Mechanical Engineering

Background:

• Autoignition at hot spots can lead to pressure pulses, causing knock in gasoline engines and detonations in ducts.
• Controlled autoignition engines exhibit benign autoignition with minimal knock.
• Understanding autoignition modes and detonation development is key to explaining engine performance.

Purpose of the Study:

• To analyze the origins of autoignition at hot spots and their relation to engine knock and duct detonations.
• To further interpret earlier studies on autoignition and detonation development using a simplified theory.
• To identify detonation regimes and their characteristics for hazard assessment.

Main Methods:

• Analysis of autoignition origins and pressure pulses.
• Interpretation of previous experimental studies (Urtiew and Oppenheim).
• Application of a simple one-dimensional theory for shock wave generation ahead of turbulent flames.

Main Results:

• An operational peninsula was identified, explaining detonation development at hot spots and engine performance.
• The theory indicates entry into autoignition domains ('explosion in the explosion') and highlights the influence of turbulent burning velocity.
• Stable and unstable detonation regimes were identified on the operational peninsula, characterized by transverse waves, triple points, and cellular structures.

Conclusions:

• Autoignition at hot spots is linked to knock and developing detonations, with an operational peninsula explaining engine performance.
• Turbulent burning velocity significantly influences autoignition, governed by localized flame extinctions.
• Further research is needed on detonation survival for hazard assessment, particularly when emerging from ducts.