A Study of Knock in Lean-Burn Spark-Ignition Engines

A study on the onset of knock in dilute spark-ignition engines was conducted on a Ricardo E6 variable compression engine. The combustion chamber was of the disc type providing the very basic shape of chambers. Various operating parameters were considered viz: equivalence ratio, engine speed, ignition timing, inlet air temperature and inlet air pressure. The onset of knock was defined by a piezo-electric pressure transducer while knock was characterized by ‘knock-limited compression ratio’. In some experiments, perforated disc-type turbulence generators with different blockage ratios were fitted immediately before the inlet valve; the object being to enhance in-cylidner turbulence and thus the effect of such turbulence augmentation on knock limit was experimentally defined. Correlations were developed to enable the onset of knock to be predicted which read:

for a gasoline with an octane number of 90. and

for a gasoline with an octane number of 80.