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Combination of flow field measurements, shown in this paper, give new information on the effect of engine run parameters to formation of different flow fields inside piston bowl. The measurements were carried out with particle image velocimetry (PIV) technique in optical engine. Good set of results was achieved even though the feasibility of this technique in diesel engines is sometimes questioned. Main challenge in diesel engines is background radiation from soot particles which is strong enough to conceal the PIV signal. Window staining in diesel engine is also a problem, since very high particle image quality is needed for velocity analysis. All measurements were made in an optical heavy-duty diesel engine. Optical design of engine was Bowditch type [1]. The engine was charged and equipped with exhaust gas recirculation (EGR). The exhaust gas level was monitored by oxygen concentration and the level was matched to former soot concentration measurements.

A detailed investigation is made of the impact of mechanical deformation on the in-cylinder volume as function of crank angle degree in an optical engine of Bowditch design. The squish height is found to change linearly with mass and pressure forces. It increases due to pressure forces and decreases due to mass forces. The thermal forces have an impact on the squish height but it is not clear in what direction. The volume change caused by deformations did not change the calculated load significantly but gave errors during heat release calculations. Two different strategies to reduce these errors are presented.