Ion Current Based Pressure Peak Detection Under Different Air Humidity Conditions

Analysis of SI Combustion Diagnostics Methods Using Ion-Current Sensing Techniques

“…These results were attained on a cycle-to-cycle prediction, with a sampling frequency of 1sample/2 o C.A., and without averaging nor information about important engine parameters such as coolant temperature, mass air flow, manifold absolute pressure etc and with relatively few "design" cycles. (Upwards of 50,000 cycles are normally used) [7,20,21]. Keeping in mind, that with a linear speed versus load table interpolation model, like the ones generally used in production vehicles today, the RMS error for PPP estimation is 3.3 C.A.…”

“…The ion recombination rate increases, and the measured ion-current signal starts to decline. This third phase of the ion-current signal is a post-flame or thermal ionization induced signal [5,6,7,8,9,10], and it is proportional to the cylinder pressure produced by combustion. Figure 1 Typical ion-current signal (and pressure signal) recorded by a central plug [2] There are some problems associated with using the spark plug as the ion-current sensor.…”

An Ion Current Based Peak-Finding Algorithm for Pressure Peak Position Estimation

“…Furthermore, the results of the peak-finding algorithm are compared to those produced by: 1. The Gaussian fit model presented in [3]. 2. The MLP model presented in [4]. Accordingly, the estimates of the latter algorithms are also low pass filtered.…”

“…However, the drawback of the algorithm is the storage needed for the parameters of the model and the preprocessing stage corresponding to approximately 1 kilobyte. For further reading see [4].…”

“…In particular, the end phase of the signal, corresponding to thermal ionization, can be related to the in-cylinder pressure. Various schemes have therefore been suggested for estimation of the in-cylinder pressure peak position (PPP) from the ion current signal [3,4,5]. These are either based on curve-fitting or pattern-matching techniques.…”