Development and Evaluation of Tracer Gas Methods for Measuring Trapping Efficiency in 4-Stroke Engines

An investigation into applying a tracer gas method for determining trapping efficiency to 4-stroke engines is carried out. The experimental errors are identified and analyzed. The errors include incomplete cylinder reaction, exhaust instability, and inconsistent exhaust sampling. Tracer gas global kinetic mechanisms are reviewed and used as a means for tracer gas selection. The tracer gases investigated are nitrous oxide (N₂O) and monomethylamine (CH₃NH₂). As a benchmark the oxygen tracer technique is analyzed, where oxygen is used as the tracer. Test results from a GM 5.7 l, 8 cylinder, 4-stroke engine are presented that include measurement of the experimental errors and the trapping efficiency. Of the tracers considered, N₂O is determined to be optimal for the engine tested.