A/F Estimation from Internal Combustion Engine Cylinder Pressure Using Fast Fourier Transform Descriptors

Fast, accurate, measurements of the A/F in each cylinder are desirable in order to provide the fastest, most efficient transient control of engines. This paper presents a new algorithm for A/F estimation based on Fast Fourier Transform descriptors and compares it to a previous algorithm based on moments. It has been used to estimate the A/F from cylinder pressure on a single cylinder engine over its entire operating regime. Computational efficiency and overall fitting accuracy of the two algorithms are evaluated and compared using the same data base. The FFT method requires approximately one half the computational requirements at a given integration step size; however, its accuracy compared to moment based algorithms is somewhat degraded. For a given amount of computational power, the moment algorithm provides superior accuracy.