Hi Marliana,
As per my understanding of the question the Brake Specific Fuel Consumption (BSFC) vs time graph from Spark Ignition (SI) engine output in MATLAB is used to analyze the performance of the engine in terms of fuel efficiency over time.
The graph shows how the BSFC values change over time.If the curve is fluctuating or increasing over time, it indicates that the fuel efficiency of the engine is not consistent and may need to be optimized. Peaks in the graph indicate periods of high BSFC, while valleys indicate periods of low BSFC.
I hope the above information helps resolve your query.
Thanks