In motorcycle engines, backfires can become an issue with increased cylinder bore size. It has been thought that backfires are caused by an extra ignition at an overlapping top dead center or by backflows into combustion chamber of high temperature exhaust gas during exhaust stroke. As a result of taking pressure measurements inside the combustion chamber, at the inlet and exhaust ports, and of observing the inside of the combustion chamber with a high speed CCD camera, it was found that an extremely slow-burning cycle exists which continuously burns during the exhaust stroke. Further, it was confirmed that the extremely slow-burning cycle caused the fresh air-fuel mixture introduced in the subsequent intake stroke to ignite thus generating backfires. This paper provides an overview of the investigation and describes some of the factors that influence the extremely slow burning cycle.
Article of Honda R&D Technical Review Vol.13 No.1 (41 - 48)