Experimental and numerical investigations of heat transfer characteristics of a piston cooling bore impinged by SAE 30 oil

The jet impingement technique is currently one of the most efficient cooling solutions for highly reinforced pistons of large two-stroke engines. To study the heat transfer characteristics of piston, experimental and numerical investigations with a piston cooling bore impinged by SAE 30 oil were carried out. To investigate the heat transfer coefficient distributions over the target bore, the wall temperatures of the cooling bore were measured by thermocouples, which will also be used in the numerical calculation. The jet Reynolds number (Re) ranges from 220 to 330, and the jet-to-plate spacing ratios (H/D) range from 10 to 30. Results show that jet-to-plate spacing ratios have a slight effect on the heat transfer coefficient for this low Reynolds numbers impingement which is quite different from high Reynolds numbers flow. There are both three peaks of the local heat transfer coefficient for Re = 330 and 280 along the x-axis direction. However, only two peaks occur when Re = 280. The heat transfer coefficient increases with the increase of Reynolds number when x/D < 0.22 or x/D > 1.77 while the variation is contrary when 0.22 < x/D < 1.77. The average heat transfer coefficient of the top surface region is far larger than other regions and decreases significantly in the upper chamfered region. While it is almost identical in the cylindrical region for different Reynolds numbers. This study provides the heat transfer characteristics of piston cooling with SAE30 oil and can be used for the piston optimization of large two-stroke engines with high cooling performance requirements.