Thermal Barrier Pistons and Their Effect on the Performance of Compound Diesel Engine Cycles 830312

The paper describes the basic design concept of a heat barrier piston comprising a Nimonic crown separated from the aluminium piston body by an air gap. Heat flow, temperature and stress levels have been evaluated using a series of specially developed finite element programs.
Preliminary experimental results obtained with the insulating piston on a Petter PH1 W engine indicate a very substantial rise in exhaust temperature, coupled with considerable reduction in volumetric efficiency under naturally aspirated conditions.
In a final theoretical section, the effects of insulated pistons and of insulated cylinder walls in general are discussed both with respect to their effect on thermodynamic cycle parameters and to the possibility of substantial improvements in thermal efficiency using the compounding principle. Final guidelines are laid down for the most effective use of thermal insulation in compounded Diesel engines.


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