Chart for the Investigation of Thermodynamic Cycles in Internal Combustion Engines and Turbines

Abstract

The development of the internal combustion turbine engine has reawakened interest in the study of thermodynamic problems associated with internal combustion engines. Graphical solutions find favour because ( a) widely varying mixtures of gases are used in modern engines, ( b) the specific heats of the gases vary with temperature and pressure, and ( c) the complete combustion of hydrogen, carbon, etc., cannot occur at high temperatures owing to dissociation. In the paper it is shown by suitable selection of scales how the temperature-internal energy graph may be used to indicate enthalpy, and, for engine expansions, the work done and the energy supplied. In turbines and turbo-compressors the heat drop, velocity change, losses, etc., are given by readings from the temperature and internal energy graph. The method is applied to a general cycle which embraces the Otto, Diesel, Atkinson, Humphrey, etc., cycles. To determine the work done and efficiency calculation is eliminated entirely. An indicator diagram taken from an oil engine is examined and the heat exchange for arbitrarily chosen parts of the cycle estimated. Internal combustion turbine cycles are discussed and the advantages of stage reheating and inter-cooling demonstrated. Energy-mixture strength tables, for temperature intervals of 200 deg. C. (360 deg. F.), are supplied for mixtures between 100 per cent weak and 20 per cent rich.