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This paper presents an experimental study of the cycle-averaged, local surface heat transfer, from the exhaust gases to a straight pipe extension of the exhaust port of a four-cylinder spark-ignition (SI) engine, over a wide range of engine operating conditions, from 1000 rpm, light load, through 4000 rpm, full load. The local steady-state heat flux was well correlated by a Nusselt-Reynolds number relationship that included entrance effects. These effects were found to be the major contributor to the local heat transfer augmentation. The Convective Augmentation Factor (CAF), which is defined as the ratio of the measured heat flux to the corresponding heat flux for fully-developed turbulent pipe flow, was found to decrease with increasing Reynolds number and increasing axial distance from the entrance of the test section.

In this study, the performance and emissions characteristics of an uncooled, thermally insulated diesel that utilized an optimized injector-tip configuration are examined. When the uncooled engine was compared to a conventional water-cooled engine at the same brake power and airflow, the uncooled engine had equal or superior fuel consumption, significantly higher nitric oxide emissions, and significantly lower smoke and particulate emissions. The dramatic reduction in smoke emitted by the uncooled engine was not observed in studies reported earlier. This smoke reduction is attributed to the high gas temperatures and increased rates of air-fuel mixing that augmented the rate of oxidation of the soot particles when the injector tip was optimized for the uncooled engine and airflow was adjusted to match that of the cooled engine. Heat-release analyses showed that the uncooled engine had less premixed combustion and significantly shorter combustion duration than the water-cooled engine.