100 125 150 175

FUEL, mg/stroke

Figure 7. Surface temperature swing at bowl location.

They show a gradual increase with increasing load, reaching values of 120K at the highest-load point measured. Extrapolating to the maximum load range one can expect swings on the order of 180K. These magnitudes of surface swings agree well with the theoretical predictions made by Morel et al (1985).

The total heat flux results obtained at the bowl position at 1300 rpm are presented in Figure 8. As in the cooled engine experiments, the heat flux level is relatively low during the compression stroke, increasing sharply near the TDC when the combustion begins. (Note that the start of combustion advances with increasing load as the Cummins P-T injector advances start of injection with load, keeping the end of injection constant.)

The heat flux in the crown location at 1300 rpm is shown in Figure 9. It differs significantly from the bowl data. Its values are substantially lower, consistent with the shielding effect of the piston crown. A similar observation was made previously in the cooled engine experiments. All of the experimental data points were simulated by the IRIS code to generate the heat flux predictions using the flow-based heat transfer model. Their comparison to the data is included in Figures 8 and 9. The model, by its nature, shows a gradual, consistent increase in the heat flux level with increasing load, and the shape of the curves also evolves in a consistent manner. There is of course more variation in the measured data. The predicted peak heat flux values (Figure 10) are sometimes higher and sometimes lower than the measured ones. Overall the agreement is quite good, and this includes the ability of the model to differentiate between the two spatial locations showing the large differences observed in the data.

It is important to note that the heat flux in the insulated engine was lower than in the cooled engine. Recently, questions have been raised by some investigators (Furuhama and Enomoto, 1987 and Woschni,et al, 1987) who claim to have observed an increase in the peak heat flux with insulation (and rising wall temperature). However, as can be seen in Figure 11, in the present experiment a definite decrease in peak heat flux was observed.

0 0

Post a comment