Knock in Internal Combustion Engines

Abstract

THE information given in the two letters¹ on the above subject by D. Downs and A. D. Walsh confirm and considerably extend, with improved equipment and procedure, the observations and conclusions to which the authors refer in the paper by Egerton, Smith and Ubbelohde². In that work it was found that nitrogen peroxide appeared to promote knock when the engine was run with hydrogen, and it was, indeed, suggested that the nitrogen oxides, in the circumstances, tended to sensitize the mixture. Lead tetraethyl was not found to suppress the knock. A fixed-compression Delco engine (6·75 : 1) had been used, and it now appears probable that the conditions were such as gave pre-ignition rather than true knock, and that lead tetraethyl has little effect in inhibiting the pre-ignition but prevents the knock. It would be interesting to test whether hydrogen will knock when no nitrogen or organic vapours are present (for example, using an argon atmosphere and a minimum of lubricating oil).