## 3 Results & Discussion
### Frequency Analysis and Malfunctioning Conditions Mapping  
In accordance to the methodology in Section 2.1, by performing a frequency analysis on the flywheel ICT, the engine harmonic frequencies with the most affected modulus and phase angle are determined as a result of the malfunctioning conditions. In specific, according to Figure 6, it is deduced that the change in SOI and RHR for the malfunctioning cylinder no. 2, affects mostly the modulus of the 28 th and the 34 th harmonic frequencies, and the phase angle of the 14 th harmonic frequency. The rest harmonic frequencies affected are observed to be identical for both malfunctioning conditions, which as mentioned in Section 3.2 confirms that both the change in SOI and RHR have a similar effect on the flywheel ICT. Furthermore, the change in scavenge air pressure and blowby modulus is on average 14.3 Nm less for their respective harmonic frequencies, compared to the change in SOI and RHR malfunctioning conditions. However, the harmonic frequencies with the most affected modulus for the change in scavenge air pressure and blowby, are lower by an average of 12 harmonics as compared to the change in SOI and RHR. Therefore, it can be distinguished from noise, and thus it can readily measure their modulus with adequate accuracy.  
The results shown in Figure 6 can be condensed to perform the malfunctioning conditions mapping, which includes the harmonic frequencies of the top three most affected frequency moduli and phase angles for every malfunctioning cylinder, as shown in Figure 7a,b respectively. It is visible in Figure 7, that specific malfunctioning conditions have a distinct effect on the flywheel ICT harmonic frequencies for all cylinders, which makes them easily identifiable by employing this mapping process. In specific, as shown in Figure 7a, the modulus of distinct harmonic frequencies is affected for the case of blowup. Hence, the modulus of the 1 st harmonic frequency for malfunctioning cylinders 2-10, and the modulus of the 4 th harmonic frequency for malfunctioning cylinders 1, 2, 4, and 10 are affected. Similarly, for the change in scavene air pressure the modulus of the 3 rd and 5 th harmonic frequencies is affected distinctly, for all engine cylinders malfunctioning. As a result, the above suffices to diagnose blowby or a change in scavene air pressure if they occur individually, to all 10 cylinders respectively.  
However, the change in SOI and RHR have a very similar impact on the flywheel ICT, hence the modulus of the nearly identical harmonic frequencies is affected, as shown in Figure 7a. This makes it difficult to distinguish weather a change in SOI or RHR is responsible when a specific cylinder is malfunctioning. In specific both malfunctioning conditions affect the modulus of the 4 th harmonic frequency for malfunctioning cylinders 3, 5, 6, and 8, as well as the 8 th and 9 th harmonic frequencies for malfunctioning cylinders 4 and 8 respectively. For the remaining cylinders, the affected moduli are exceeding the 10 th harmonic frequency which can make them difficult to distinguish from noise in the flywheel ICT signal. However, as shown in Figure 7b, the most affected phase angle of the 4 th harmonic frequency corresponds to both malfunctioning conditions, for cylinders 1, 2, 7, 9 and 10. As a result, since phase angle of a lower harmonic frequency is affected as compared to the effected modulus harmonic frequencies, the effect of both malfunctioning conditions is easier to identify for all 10 cylinders respectively.  
Figure 6: Change in the (**a**) modulus and (**b**) phase angle of the top three most affected engine harmonic frequencies from a malfunction of cylinder 2, at 100% load. Most affected frequencies are denoted with the letter F at the top of each bar.  
Figure 7: Mapping of individually occurring malfunctioning conditions for each cylinder showing the harmonic frequencies with the most affected (**a**) modulus and (**b**) phase angle, at 100% load.