Search Results

A set of heat flux data was obtained in a Cummins single cylinder NH-engine coated with zirconia plasma spray. Data were acquired at two locations on the head, at several speeds and several load levels, using a thin film Pt-Pt/Rh thermocouple plated onto the zirconia coating. Careful attention was given to the probe design and to data reduction to assure high accuracy of the measurements. The data showed that the peak heat flux was consistently reduced by insulation and by the increasing wall temperature. The mean heat flux was also reduced. The results agree well with a previously developed flow-based heat transfer model. This indicates that the nature of the heat transfer process was unchanged by the increased wall temperature. Based on these results, the conclusion is drawn that insulation and increasing wall temperatures lead to a decrease in heat transfer and thus contribute positively to thermal efficiency.

Detailed heat transfer measurements were made in the combustion chamber of a Cummins single cylinder NH-engine in two configurations: cooled metal and ceramic-coated. The first configuration served as the baseline for a study of the effects of insulation and wall temperature on heat transfer. The second configuration had several in-cylinder components coated with 1.25 mm (0.050″) layer of zirconia plasma spray -- in particular, piston top, head firedeck and valves. The engine was operated over a matrix of operating points at four engine speeds and several load levels at each speed. The heat flux was measured by thin film thermocouple probes. The data showed that increasing the wall temperature by insulation reduced the heat flux. This reduction was seen both in the peak heat flux value as well as in the time-averaged heat flux. These trends were seen at all of the engine operating conditions.

An experimental study was conducted to measure the heat transfer in a direct injection 2.3 ℓ single cylinder diesel engine. The engine was operated at speeds ranging from 1000 to 2100 RPM and at a variety of loads. The heat transfer was measured using a total heat flux probe, operating on the principle of a thin film thermocouple, sensitive to both the convective and radiative heat flux. The probe was located in the head at two locations: opposite the piston bowl and opposite the piston crown (squish region). The measurements showed about twice as large peak heat flux in the bowl location than in the crown location for fired conditions, while under motoring conditions the relationship was reversed and the peak heat flux was slightly higher in the crown position. The experimental profiles of total heat flux were compared to the predictions obtained using a detailed thermodynamic cycle code, which incorporates highly resolved models of convective and radiative heat transfer.