Evaluation of a spark ignition engine cycle using first and second law analysis techniques

In the present work, a simulation model of the actual processes occurring during the thermodynamic cycle of a real spark ignition engine is developed. The model incorporates such important features as heat exchange of the cylinder gases with the chamber walls (during all phases), real spark ignition timings, real valve opening and closing timings, accurate simulation of the spherical flame front movement issuing from the spark plug and calculation of eight chemical species concentration during combustion, at every engine degree crank angle. The results from this first law analysis of the real cycle (for example pressure indicator diagrams, efficiencies) are compared favourably with the relevant experimental results obtained from a flexible, variable compression ratio, Ricardo E-6 spark ignition engine, located at the author's laboratory, forming thus a sound basis for moving towards a second law evaluation of this cycle. The thermodynamic state points, determined from the first law analysis, are used to determine the availability (second law analysis) at each engine crank angle and so lead to the effectiveness computation, as well as to the revelation of the magnitude of the work-potential lost during the various processes in a much more realistic way than the first law analysis can. The second law analysis results, for the actual engine in hand, are compared with the up-to-now existing ideal cycle Otto engine results. Also, a second law parametric investigation is performed over a wide range of design and operation conditions (compression ratio, fuel-air ratio, ignition advance), providing useful information for the cycle processes performance assessment by bringing state degradations and thermodynamic losses into perspective.