This paper describes the influence of a rapid throttle opening on the charging process, the mixture formation, the ignition timing and the transient performance of an engine.
The two main reasons for disturbances in the transient response are imperfections in mixture formation and in ignition timing.
These phenomena will be analysed using a single cylinder and a four cylinder engine. For the single cylinder engine a detailed analysis of every cycle is possible during a rapid throttle opening. This will be done by computations, using measured initial and boundary conditions in order to show the variation in the air-fuel equivalence ratio during the transient.
For the 4 cylinder engine it is almost impossible to carry out the same detailed analysis, because it is difficult to estimate the individual volumetric efficiency of each cylinder. But with the computational model used it is possible to give a first estimate about the transient response and the imperfections in mixture formation which can be expected.
The importance of these investigations becomes clearly evident when the correlation between deviations from stoichiometric air/fuel ratio and the reduction of catalyst life time is considered.