Parametric Study of the Availability Balance in an Internal Combustion Engine Cylinder

The current work uses a method developed by the authors for both combustion irreversibility and working medium availability computations in a high speed, naturally aspirated, four stroke, internal combustion engine cylinder. The objective of the study was to extrapolate already published results of the second-law analysis of diesel engine operation by studying parametrically the effect of main operating parameters such as engine speed of rotation, injection timing, and fuel composition. Extensive experimental data were available for the case of dodecane injection, which were used for the determination of the fuel reaction rate. Computationally, the same reaction rates were used for methane and methanol injection. The production rate of irreversibility during combustion was analytically calculated as a function of the fuel reaction rate with the combined use of first and second-law arguments and a chemical equilibrium hypothesis. Also, the differential variation of working medium availability is computed throughout the engine cycle. Both of these quantities can be integrated during the cycle to yield a total “combustion loss” and the exhaust gas availability. The “combustion loss” is a measure of the entropy created during combustion, which cannot be revealed by first-law analysis. It can be used to test theoretical expectations, e.g. that limited cooling can increase efficiency and that the decomposition of lighter molecules (CH₄,CH₃OH) would create less entropy increase compared to the heavier fuel case (C₁₂H₂₆). Also, the exhaust gas availability contains more information than its enthalpy counterpart as far as the possible operation of exhaust gas heat recovery devices is concerned. Such devices include exhaust gas turbines and Rankine bottoming cycles and are restricted in their operation by second-law arguments in a manner that cannot be evaluated by first-law analysis.