Analysis of In-Cylinder Heat Transfer in Larger Bore Engines
A study of large-bore-engine power-cylinder heat transfer is nearing completion. Quantification of both instantaneous and cycle-integrated heat transfer is essential for accurate combustion-pressure-based heat-release analysis as well as emission-formation modeling. Extensive heat-transfer measurement and modeling efforts on automotive and heavy-duty truck engines have been performed and reported on in the literature, but very little of such work focused on large-bore engines has been published. Large-bore engines typically have cylinder diameters greater than 25 centimeters and can be as large as one meter or more. The operating conditions are vastly different than those seen in automotive or heavy-duty applications; consequently, it is reasonable to believe audits of energy usage could be significantly different. To date, when performing simulation or cylinder-pressure-based combustion-analysis calculations, the heat transfer between the combustion-chamber gasses and the cylinder wall (know as in-cylinder heat transfer) is either ignored or assumed to behave similarly to automotive or heavy-duty engines. These assumptions will be tested by analyzing combustion-chamber surface-temperature measurements made in a Cooper GMC engine. These temperature measurements will be converted to local surface-heat-transfer calculations then integrated over the combustion-chamber surface to determine total gas-to-wall heat loss during the combustion cycle. An energy audit will then be performed by comparing these results to total fuel added, work energy out, frictional losses and heat energy lost to exhaust in order to determine the relative importance of in-cylinder heat transfer.