VELOCITY AND RATE OF FLOW MEASUREMENTS IN INTERNAL COMBUSTION ENGINES

Measurement of both the mean and instantaneous values of gas velocity in internal combustion (i.c.) engines presents problems of considerable difficulty and the application of electronic methods of measurement has made important contributions in this field. The problems encountered in metering pulsating flows are briefly discussed with special reference to the advantages of two metering devices which employ electronic circuits. Whilst pressure transducers enable the variation in instantaneous gas velocities to be inferred in certain circumstances there are many other cases where a direct indication of velocity variation is desirable. The hot wire anemometer (h.w.a.) has been highly developed for aeronautical engineering applications but special problems arise in the reciprocating engine where velocity variations can be large. This paper describes a constant temperature h.w.a. using a d.c. circuit which has proved stable and relatively easy to operate. If velocity measurements in the engine cylinder are required the problem becomes a three-dimensional one, and the response of the h.w.a. to variation in flow direction is discussed. Consideration is given to materials suitable for probe wires