AbstractIn spite of its known shortcomings as a fuel for spark ignition engines, acetylene has been suggested as a possible alternative to petroleum‐based fuels since it can be produced from non‐petroleum resources (coal, limestone and water). Therefore, acetylene was evaluated in a single‐cylinder engine to investigate performance and emission characteristics with special emphasis on lean operation for NOxcontrol. Testing was carried out at constant speed, constant airflow and MBT spark timing. Equivalence ratio and compression ratio were the primary variables.The engine operated much leaner when fuelled with acetylene than with gasoline. With acetylene, the engine operated at equivalence ratios as lean as 0·53 and 0·43 for compression ratios of 4 and 6, respectively. However, the operating range was very limited. Knock‐induced preignition occurred either with compression ratios above 6 or with mixtures richer than 0·69 equivalence ratio.Both the indicated thermal efficiency and power output were less for acetylene fuelling than for gasoline.Acetylene combustion occurred at sufficiently lean equivalence ratios to produce very low NOxand CO emissions. However, when the low NOxlevels were achieved hydrocarbon control was not improved over that with gasoline.Despite the potential for NOxcontrol demonstrated in this study of acetylene fuelling, difficulties encountered with engine knock and preignition plus well‐known safety problems (wide flammability limits and explosive decomposition) associated with acetylene render this fuel impractical for spark igni