The Origin of Pressure Waves in High Load HCCI Combustion: A High-Speed Video Analysis

Abstract

Homogeneous charge compression ignition is an alternative combustion strategy for spark-ignited gasoline engines that improves engine efficiency and thus reduces CO₂ emissions, which is crucial to meet targets set by legislation. However, this combustion strategy is limited to low loads, mainly due to pressure oscillations that arise if combustion is too rapid. The aim of the work described in this article was to record and identify these pressure oscillations and correlate them with the preceding combustion. This was performed using an image-intensified high-speed video camera with a sampling rate of 111 kHz filming inside the combustion chamber of an engine with optical access through a quartz piston. A strategy is described whereby video analysis is used to extract the acoustic modes resulting from combustion. In this work it was possible to detect four different acoustic modes. It is shown that the type and magnitude of these modes can be correlated to the size and position of combustion chamber zones with rapid combustion and the light intensity development (combustion speed) in these zones. It is also shown that the highest combustion rates occur in regions where combustion starts late.

Keywords:

• Acoustic modes
• CAI
• HCCI
• High-speed video
• Knock
• Pressure waves
• Ringing

ACKNOWLEDGMENTS

The authors would like to thank the Swedish Energy Agency and Volvo Car Corporation for financial support. Volvo Car Corporation is also acknowledged for supplying experimental equipment and support. We are also grateful to Allan Sognell and Lars Jernqvist at Chalmers engine research laboratory for help with the experimental equipment.