Ignition and boost effects on large-bore engine in-cylinder heat transfer

One cylinder of the Colorado State University large-bore test engine was instrumented with fast-response surface thermocouples for heat-transfer analysis. Probes were installed at several locations progressively farther from the ignition source and their outputs were recorded along with combustion pressure using a high-speed data-acquisition system. The engine was operated with two different ignition methods and the manifold boost pressure and cylinder jacket water temperature (JWT) were varied. The recorded surface temperature data were processed to calculate in-cylinder heat transfer. Combustion initiated with a screw-in type pre-combustion chamber resulted in significantly different characteristics than that initiated by a conventional spark plug. The differences in peak heat-flux value could likely be attributed to flame quench distance. Differences in other portions of the cycle could have been caused by significantly increased flame velocities associated with the pre-chamber jet. Increasing boost pressure from 25 to 54 kPa decreased peak heat-flux values about 20–30% and steady-state values about 13%. Increasing JWT 14 K had an insignificant effect on heat flux and combustion pressure.