The engine simulations have become an integral part of engine design and development. They are based on approximations and assumptions. The precision of the results depends on the accuracy of these hypotheses. The simplified models of frozen composition, chemical equilibrium and chemical kinetics provide the compositions of combustion products for engine cycle simulations. This paper evaluates the effects of different operating conditions and hypotheses on the exergetic analysis of a spark-ignition engine. The Brazilian automotive market has the highest number of flex-fuel vehicles. Therefore, a flex-fuel engine is considered for simulations in order to demonstrate the effects of these different hypotheses. The stroke length and bore diameter have the same value of 80 mm. The in-cylinder irreversibility is calculated for each case at the closed part of the engine cycle. A comparative analysis of these hypotheses provides a comprehensive evaluation of their effects on exergetic analysis. Higher values of accumulated irreversibility are observed for the oversimplified hypothesis.

Power generation units, suitable for individual users and small scale applications, are mainly based on spark ignition engines. In recently performed research, reductions of emissions coming from such units, especially considering carbon dioxide emissions, are deemed as the issue of particular importance. One of solutions, postponed to reduce impact of spark ignition engine-based units on the natural environment, is transition from fossil fuels into renewable gaseous fuels, as products of organic digestion. Nonetheless, development of new solutions is required to prevent further carbon dioxide emissions. The paper presents a novel dual approach developed to reduce carbon dioxide emissions from stationary power units, basing on spark ignition engine. The discussed approach includes both reduction in carbon content in the fuel, which is realized by its enrichment with hydrogen produced using the solar energy-supported electrolysis process, as well as application of post-combustion carbon dioxide separation. Results of the performed analysis suggest profitability of transition from fossil into the hydrogen-enriched fuel mixture, with significant rise in operational parameters of the system following increase in the hydrogen content. Nevertheless, utilization of the carbon dioxide separation leads to vital soar in internal energy demand, causing vital loss in operational and economical parameters of the analyzed system.