Knock in Spark Ignition Engines
The knocking characteristics of several fuels are studied using a single cylinder test engine with variations in key engine operating parameters. Compression ratio, spark advance, fuel equivalence ratio, exhaust gas recirculation, engine speed, charge inlet pressure and charge inlet temperature were varied to yield a range of engine cylinder pressure-temperature histories as the base for this study. The fuels studied include three reference fuels containing isooctane and heptane with isooctane volume percents of 80, 90 and 100. Two wide boiling range gasolines were also studied. A number of empirical relationships for autoignition times of isooctane and heptane blends are employed in conjunction with the experimentally obtained pressure-temperature histories to predict onset of knock. The accuracies of the predictions with respect to the experimentally determined knock points are discussed.