Heat Loss to The Combustion Chamber Wall with Deposit Adhering to The Wall Surface in D.I. Diesel Engine First Report: Influence of Deposit on Instantaneous Heat Flux into The Piston Surfaces

One of factors affecting the state of heat loss to the wall of D.I. diesel engine is the adhesion of deposit on the combustion chamber wall surfaces. In diesel engines currently used in practice, such deposit is normally adhered to the wall surface. Therefore, determination of the effects of deposit on the state of heat loss is also necessary for the comparison with the state of heat loss measured in experiments conducted without deposit. The effects of deposit, however, have not been clearly determined due partially to the complexity involved in the amount and the state of deposit which differ according to differences in time and location. In this regard, the authors et al. decided to make an attempt on clarification of the effects of deposit.

Instantaneous heat flux has been measured at plural points on a piston surface with the adhesion of deposit, and the variation of heat flux has been also studied, which will be presented as the first report in this paper. For the purpose of measurement, thin-film thermocouples were embedded into the piston cavity, and the instantaneous surface temperatures at different portions in the process of deposit accumulation were measured and the values of instantaneous heat flux were calculated accordingly. As a result, it is found that the instantaneous surface temperature and instantaneous heat flux on the piston surface vary according to the difference in the amount of deposit adhered. That is, as the amount becomes greater, the phase showing the maximum value of instantaneous surface temperature tends to delay, and the temperature up and down gradient and the amplitude become smaller. Similar tendencies are also found in instantaneous heat flux, with a gentler heat flow to the piston surface per cycle.