THUDDING in High Compression Ratio Engines

THUD—a noise due to high rates of pressure rise in the absence of surface ignition—is the subject of the investigations described in this paper. The tests were performed on 12/1 compression ratio engines.

The authors found that thud could be obtained both in engines with clean combustion chambers and those with deposits. Thud is most likely to occur in 12/1 compression ratio engines at least — at wide-open throttle, high speed, and high spark advance.