Procedures in Sampling and Handling Auto Exhaust

Both the composition and discharge rate of auto exhausts vary widely and rapidly as speed and load demands upon the engine are changed. Moreover, among the combustion products are compounds that are highly reactive under proper conditions and others that are readily bound by receptive surfaces or absorbents. Under these conditions both the sampling procedure and subsequent sample handling must be such that (1) the sample that is recovered contains all or a fixed proportion of each incremental volume of the total to be represented and (2) the products so sampled are not allowed either to react with each other or to be lost or diminished in sample storage or transfer. Experimental research and development relevant to each requirement have been carried out, and results are reported and discussed. Two methods have been used for recovering sample-volume samples representative of the total volume produced during any combination of steady or transient engine modes. One employs a servo-followup system appropriately coupled to both the engine air-intake and to the sampling element; the sampling rate is continuously controlled to bear at all times a fixed ratio to the engine air-intake rate. The second method employs variable dilution, involving addition of diluent gas necessary to maintain a constant total of exhaust + diluent]. If the mixture is sampled at a constant rate, the sample will contain exhaust appropriately proportioned. Experiments have shown differences in both hydrocarbon and NO_x values determined for comparable samples obtained by the two methods. The seriousness of this problem is discussed in relation to the sampling and sample handling procedures that are used.