Figure 3 Plot of the function g used in the throttle block.

Since the fuel-air mixture flows into the engine once in every two revolu­ tions, the output o f these blocks must be sampled and held. The fuel-air charge that the engine burns is sampled in the Simulink model using the integrator block. Looking at this block in Fig. 5, the integrator block has two inputs and two out­ puts. These input and output ports are set by a dialog box that is opened by double clicking the integrator block. The input is the mass flow rate into the engine. The trigger causes the integrator to sample the integrated input whenever the engine cycles through two complete revolutions.