Cyclic variations in engines have been the subject of much investigation and there are some excellent reviews of this research. However, there is still a need to examine in an integrated manner the cyclic variation in performance parameters such as indicated power output, efficiency and cylinder pressure development in relation to the cyclic variation in some important combustion parameters notably those of the ignition lag, which is the time requirements to initiate a flame kernel following the passage of a spark and the duration to complete the combustion process particularly when gaseous fuels, notably methane are used.
The paper describes the results of an investigation with these objectives using a single cylinder, variable compression ratio, spark ignition, CFR engine, run at constant speed, operating mainly on natural gas. Through the use of a data-acquisition system, engine performance, the corresponding combustion characteristics and associated cyclic variation were established. The presence of some diluents such as nitrogen or carbon dioxide and other gaseous fuels with the methane were also considered.