An Analysis on Heat Loss of a Heavy-Duty Diesel Engine by Wall-Impinged Spray Flame Observation

Impingement of a spray flame on the periphery of the piston cavity strongly affects heat loss to the wall. The heat release rate history is also closely correlated with the indicated thermal efficiency. For further thermal efficiency improvement, it is thus necessary to understand such phenomena in state of the art diesel engines, by observation of the actual behavior of an impinging spray flame and measurement of the local temperature and flow velocity. A top-view optically accessible engine system, for which flame impingement to the cavity wall can be observed from the top (vertically), was equipped with a high speed digital camera for direct observation. Once the flame impinged on the wall, flame tip temperature decreased roughly 100K, compared to the temperature before impingement. With higher injection pressure, local flame speed, as determined by the PIV technique was almost the same as that determined by numerical simulation, whereas flame temperature near the wall analyzed by the two-color method showed a relatively smaller increase than the numerical results. The experiment was also carried out with zirconia coated combustion chamber, which resulted in a 100 K lower flame tip temperature drop than the baseline steel piston did, in the impingement region.