Measurement and Prediction of the Heat Flow and Temperature Level in a Precombustion Chamber Diesel

Heat flux and temperature mapping were carried out in necessary detail in the combustion chamber of a pepper-pot type pre-combustion chamber diesel engine.

A test set up was specifically prepared for this purpose in which heat fluxes were measured by specially designed traversing thermo couples, four of which were installed across the cylinder head and five were fitted along the cylinder liner. In combustion chamber locations not subjected to very high heat flows viz pre-combustion chamber tip, fuel-injection nozzle tip, exhaust valve..etc but their temperature level is the all-important factor in service, fixed microthermo couples were embedded in the metal as close as possible to the gas face of the component. The widest possible variation in load and speed was applied and it was found that the predominant factor affecting the heat flux and temperature level was the fuelling rate unit piston area, effected by engine load and/or speed. Qualitative evidence suggests that piston heat fluxes follow the same pattern of that in the cylinder head. Heat flux and temperature level correlations were developed for the various combustion chamber components.

Heat fluxes and metal temperatures seemed to follow the direction and intensity of air swirl. Thus they proved to be considerably higher in the present engine in comparison with compression-swirl or induction swirl engines. As a result, pre-combustion chamber engines will be more difficult to uprate than comet or direct-injection engines and thus will require modification more readily. Contrary to most other types of engines, the centre region of the cylinder head of the present engine which encompasses the valve bridge, did not exhibit the highest thermal load. In fact the outer locations of bore are the critical zones in design.