A Cycle Simulation And The Second Law Of Thermodynamics Analysis For SI Engines Using Oxygen Enriched Combustion Air

The use of oxygen enriched combustion air for internal combustion engines has been of interest for many researchers. Its advantages include higher power densities output and lower cold-start emissions. The author of this paper employ software GT-Power to get simulation for a naturally aspirated SI engine, analyzing the differences that the inlet oxygen enrichment makes; and the author has a the second law of thermodynamics analysis for in-cylinder combustion, heat transfer, exhaust emission. Under the inspiration of the exergy distribution results, at the end of the paper, the author has a preliminary simulation for the adiabatic oxygen enriched engine.The paper make a comparison of five different oxygen volumetric concentration cases include 21%,23%,25%,27%,29%.The simulation result indicated as follows:For an increase of oxygen concentration from 21% to 25%,the engine brake power and maximum braking torque increase largely; while from 25% to 29% oxygen concentration, the braking power and maximum braking torque increase slightly. Both braking power and maximum braking torque at 29% oxygen increase by 16% than normal air. Also for 21% oxygen to 25% oxygen, the indicated efficiency and heat loss increase obviously; for 25% oxygen the heat loss percentage of total energy is larger than normal air, the growth is up to 25%.Judging from the maximum temperature, from 2643.1K at 21% oxygen grows up to 2851.7K at 25% oxygen, and form 25% to 29%,the temperature almost keep constant. The increase of maximum temperature in cylinder is the direct reason for heat loss.From the 21% oxygen concentration to 25% oxygen concentration, the engine braking thermal efficiency monotonically increase and form 25% to 29%, the braking thermal efficiency almost keep unchanged even has a tendency to decrease. The braking thermal efficiency at 25% oxygen is larger by 4 percentages than normal air.Judging from the date of specific indicated efficiency, the specific indicated efficiency increase as the oxygen concentration increase. At 29% oxygen the specific indicated efficiency is 27.27 kW/dm3, which is larger by 14.7% than normal air. So if engine put the oxygen enrichment into practice, engine can reduce the engine size but maintaining the power unchanged.For five concentration of oxygen in air 21%,23%,25%,27%,29%, the CO concentration in exhaust as a function of crank angle have the same trends. From the TDC point, it increase dramatically due to temperature increase, up to the maximum value at combustion point, and then have a sharp decline until EVO point, and remain constant.Although higher oxygen concentration is helpful for decreasing the CO, the NO concentration will increase dramatically in combustion process, after maximum value it will drop gently until expansion stroke.The second law of thermal dynamic analysis result indicated that as the oxygen concentration increase, the exergy destruction in combustion decrease, and the exergy loss due to exhaust and heat transfer become higher. When the oxygen concentration is 25%, the SI engine exergy distribution in in-cylinder combustion, heat transfer, and exhaust emission is 19%,7%,42% respectively.The reaction initial pressure has no effect on exergy destruction due to combustion, however the higher initial temperature, the less exergy destruction in combustion process, and the easier to collect the exergy in exhaust, so at the end author make a simulation for adiabatic case, the result indicated that the adiabatic engine have a better power output and economic efficiency.