In engine applications, the onset of knock remains one of the prime limitations that needs to be addressed so as to avoid its incidence and achieve superior performance. In the present contribution relating to the spark ignition hydrogen-fuelled engine, the effects of changes in key operating variables, such as compression ratio, intake temperature and spark timing on knock-limiting equivalence ratios are established both analytically as well as experimentally. Some other factors considered included the optimization of spark timing for maximum indicated power output and/or efficiency and for the avoidance of knock while maintaining high thermal efficiency values. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.