Study on Combustion Chamber Geometry Effects in an HCCI Engine using High-Speed Cycle-Resolved Chemiluminescence Imaging

Författare

Andreas Vressner
Anders Hultqvist
Bengt Johansson

Summary, in English

The aim of this study is to see how geometry generated

turbulence affects the Rate of Heat Release (ROHR) in

an HCCI engine. HCCI combustion is limited in load due

to high peak pressures and too fast combustion. If the

speed of combustion can be decreased the load range

can be extended. Therefore two different combustion

chamber geometries were investigated, one with a disc

shape and one with a square bowl in piston. The later

one provokes squish-generated gas flow into the bowl

causing turbulence. The disc shaped combustion

chamber was used as a reference case. Combustion

duration and ROHR were studied using heat release

analysis. A Scania D12 Diesel engine, converted to port

injected HCCI with ethanol was used for the

experiments. An engine speed of 1200 rpm was applied

throughout the tests. The effect of air/fuel ratio and

combustion phasing was also studied. The behavior of

the heat release was correlated with high speed

chemiluminescence imaging for both combustion

chamber geometries. Optical access was enabled from

beneath by a quartz piston and a 45 degree mirror. It

was found that the square bowl in piston generates

higher turbulence levels resulting in half the ROHR and

twice as long combustion duration as the disc shaped

combustion chamber. By using a resolution of 3 images

per CAD, the fast gas movements during the entire

HCCI combustion process could be studied inside the

bowl.

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