Investigation of Extreme Mean Effective and Maximum Cylinder Pressures in a Passenger Car Diesel Engine

The current level of mean effective pressure (mep) of automotive diesel engines is 20 to 30 bar. Maximum pressure (p_max) is about 180 to 200 bar. In special applications even higher figures have been achieved in the past. This led the authors to investigate what can be expected when operating at much higher pressures. In a theoretical study the mep of a passenger car engine was increased up to 80 bar.

A zero-dimensional cycle simulation program was used for the calculations. Rate of heat release, valve timing and mechanical efficiency were kept constant. Several strategies concerning turbocharging and thermal loading were investigated. Some results for mep = 80 bar: - The specific fuel oil consumption is reduced by some 5%, if certain prerequisites are given. - Further reductions are possible depending on mechanical efficiency, which was set constant in this study. - Charge air pressure increases to approximately 10 bar. This may be possible with two stage systems. - Turbocharging efficiency should be increased with higher mep. Otherwise pumping losses increase and the improvement in sfoc is lost. An increase of at least 10% points is necessary. This may also be possible if two-stage systems with intercooling are used. - Maximum pressure increases to values above 750 bar. This is far beyond the present state of the art. New design and material solutions will be necessary to handle this.