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A literature search to identify deleterious effects of using re-refined oil did not disclose any validated occurrences. Significant engine testing using re-refined lubricating oil is reported and no cases were discovered in which engine operation was affected negatively by the use of re-refined oil. The American Petroleum Institute (API) allows the use of re-refined base stock oils in the blending of end use lubricants. Based on oil sample testing performed in this research as well as other authoritative sources, it was determined that no significant chemical or physical differences exist between re-refined and virgin oils. Differences noted in this research were related to higher levels of poly-nuclear aromatics (PNA's) in the re-refined oil. PNA's are formed due to the extreme conditions of temperature and pressure during operation of an internal combustion engine.

A single-cylinder, 4-stroke, spark-ignition engine was used to evaluate the effect of oxygen enriched air on engine performance and exhaust emissions. Evaluations were made with both gasoline and natural gas. The oxygen content of the intake air was varied between 20.9% (ambient air) and 25%. The effects of oxygen enrichment were evaluated in terms of power output, specific fuel consumption, fuel conversion efficiency, exhaust gas temperature, and exhaust emissions (carbon monoxide and hydrocarbons). Test results indicate that the use of oxygen enriched air produces a significant increase in power output, improved fuel conversion efficiency, lower specific fuel consumption, higher exhaust gas temperature and a substantial reduction in carbon monoxide and hydrocarbon emissions when the engine is fueled with either gasoline or natural gas.