Correlation of Knock with Engine Parameters for Ammonia/Nitrous Oxide Mixtures

The knock characteristics of Ammonia/Nitrous Oxide mixtures in a CFR engine were determined as a function of equivalence ratio and compression ratio. The engine speed and ignition timing were constant at 900 rpm and 13° BTDC, respectively. The gas mixture entered the engine at room conditions. Knock was sensed from measurements of cylinder pressure using a piezoelectric transducer.

The intensity of knock was assessed in terms of the third derivative of cylinder pressure with crank angle, which was determined from a computer analysis of the measured signal. In terms of knock intensity, Kl, the data indicates that for normal combustion, Kl < 3 kPa/CA³; for incipient knock, Kl = 3 to 5 kPa/CA³ and for audible knock, Kl > 6 kPa/CA³.

The knock intensity was normalized in terms of a pressure that is related to energy release per unit volume. A correlation was obtained between the normalized knock function and the equivalence and compression ratios. All data fell within 20% of the correlation equation.