Heat Transfer Characteristics of an Uncooled Silicon Nitride Surface in a Naturally-Aspired DI Diesel

Instantaneous heat flux and flame position were measured on a silicon nitride diesel engine head. Ionization probes and thin-film platinum temperature detectors were applied directly to the head surface.

The ionization probes showed that the flame exited the bowl and propagated asymmetrically from the centerline of the combustion bowl.

The temperature measurements revealed that average surface temperatures varied with position by more than 200°C. Spatial variations in the temperature swings were also present with large swings resulting from direct combustion effects on heat transfer at locations near the lip of the piston bowl.

Peak instantaneous heat flux values varied from 0.3 to 2.0 MW/m². Five of the seven probe locations exhibited heat transfer rates that were limited due to the combustion rate. At three different positions, the peak heat flux magnitude and phasing were independent of load. Comparing these locations, the time-averaged heat flux decreased with increased surface temperature.