Search

Major design features of high-tumble spark-ignition engines achieving over 40% brake thermal efficiency include a sub-square combustion chamber, less curved or more "straight" intake port shape and wider angle between the intake and exhaust valves, which are intended to enhance the turbulence at spark timing and thereby increasing the flame propagation speed. This new design requires a clear understanding of the in-cylinder flow field and its variation due to direct fuel injection into the cylinder. The present study reports a new endoscopic high-speed particle image velocimetry (eHS-PIV) technique implemented in a multi-cylinder high-tumble production engine, which can be used to acquire crucial flow field information in a timely manner with no significant resources required to develop a single-cylinder full optical engine. A laser beam at 35 kHz was inserted through a rigid endoscope (borescope) wherein a series of rod lenses producing a 60° diverging planar laser sheet to cover the pent-roof area. Hollow-glass spherical particles were supplied upstream of the throttle body. A camera borescope was installed to record particle movement at the same 35 kHz framing rate and the acquired movies of 100 cycles were post-processed using PIVLab. The feasibility tests performed in an available single-cylinder full optical engine indicated that the new eHS-PIV is applicable to direct-injection engines with both motoring flow fields and the injection-induced flow structure alteration is clearly visualised. The application of the eHS-PIV to a multi-cylinder production engine was also successful and achieved a finding of new flow structures unique to high-tumble engines and the significant enhancement effects of direct fuel injection on flow velocity and turbulence intensity. Graphic abstract [ABSTRACT FROM AUTHOR]