Technical Implementation of a Constant Volume Combustion in a Real Engine

Authors

Dipl.-Ing. B. Burger, Prof. Dr.-Ing. M. Bargende, University of Stuttgart;
Dr.-Ing. U. Philipp, Research Institute of Automotive Engineering and Vehicle Engines Stuttgart

Year

2020

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 813

Summary

The isochoric process represents the thermodynamically most efficient comparison process for gasoline engines, which is, in principle, technically realizable. Within this research project, a combustion engine with real isochoric boundary conditions is developed, manufactured and tested. A special crank drive kinematics enables a stillstand of the piston around the top dead center (TDC) within a symmetric crank angle range. This is achieved by superimposing two opposing rotary movements. Instead of the crankpin of a conventional crankshaft, a second, smaller crankshaft with an eccentric crankpin is installed. It is pivoted in the crank webs of the first and more massive crankshaft by roller bearings. The second crankshaft rotates with a ratio of two to one in opposite direction of the first crankshaft. The piston stroke and thus the compression ratio of the engine always has the same value, regardless of the selected eccentricity. No eccentricity represents the stroke of a conventional combustion engine. With increasing eccentricity, the stroke changes and allows a resting time of the piston symmetrically to TDC, by continuously rotating crankshafts. The amount of eccentricity defines the duration of the resting time. This makes it possible to compare the influences of an isochoric combustion directly with those of conventional kinematics within the same crankcase.
Concerning the measurement equipment, sensors for high and low pressure indication as well as pressure and temperature measuring quick surface temperature probes are used. This enables the temperature curves of the combustion chamber surface to be recorded within crank angle resolution. The influence of isochoric combustion is studied using operation points of constant air mass and constant air-fuel-ratio at three different crankpin eccentricities of the small crankshaft.