## 3 Engine Modifications and Mechanism Design
### Engine Modifications
Figure 1: Normalized cylinder-wise torque integrals in power balancing results: (**a**) simulations; (**b**) actual test on a medium-speed 7-cylinder diesel engine [9]. Figure 3: The transmission ratio of each mounting system at different engine speeds [14]. The rubber cone-and-shear mount offered the highest vibration isolation at all speeds. Figure 2: RMS of vibration accelerations of (**a**) engine; (**b**) chassis [14]. In their experimental study, [PERSON] and [PERSON] [22] studied the effect of air-fuel ratio and ER (\(\lambda\)) on vibration components of a gas-powered ICE equipped with an asynchronous generator. Measurements were carried out at a constant speed (1500 rpm) to maintain the frequency of the components unchanged. A short-time Fourier transform (STFT) analysis was used to determine the spectral components. During the experiments, four time signals with varying oxygen (O\({}_{2}\)) contents of the exhaust gas were recorded to measure the maximum and minimum amplitudes at different ERs (Table 1). Here, \(\infty\) means that no combustion occurred in the chamber and the engine was actuated only by the asynchronous machine. As shown in Figure 5, the amplitudes tended to drop with increasing the ER function (% O\({}_{2}\)). In other words, the vibration components decreased by degradation of the air-fuel mixture, i.e., the step-by-step garbling of the perfection of the combustion. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\Lambda\) & \(\mathbf{O_{2}}\) (\%) & \(\mathbf{A_{max}}\) (s) & \(\mathbf{A_{min}}\) (s) \\ \hline
1.06 & 1.3 & 46.57 & \(-\)54.65 \\
1.24 & 3.9 & 36.81 & \(-\)38.31 \\
1.51 & 7.6 & 31.51 & \(-\)32.49 \\ \(\infty\) & 0.0 & 29.38 & \(-\)28.97 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The maximum and minimum amplitudes of the four-measurement setup as a function of the air-fuel equivalence ratio [23]. Figure 4: Improvement in transmission ratio after applying the concentrated mass at all speeds [14]. Figure 5: Amplitude changes of some frequency component as a function of ER [23]. Figure is reprinted with permission from publisher. [PERSON] et al. [23] investigated mitigation of noise and vibration in a direct injection gasoline (DIG) engine by optimizing the geometry of its high-pressure fuel pump, without affecting the fuel consumption and emissions of the engine. Figure 6a illustrates schematic of a typical DIG, composed of different components. Fuel system, the heart of the DIG, contains a high-pressure fuel pump, fuel pipes, and injectors. It is considered as the main source of noise generation in the DIG engines. Since the pump and injectors are typically solenoid-actuated, the vibration can be reduced or diminished if accurate design and control modifications are applied to the system. For the former, vibration damping could be improved by applying changes to the fuel rail/cylinder head and injectors/cylinder head mountings. Hence, those researchers sandwiched a rubber isolator between the fuel rail clips and cylinder head, to isolate the system noise and eliminate the vibration transmission path to the cylinder head (Figure 6b). Furthermore, the cylinder head vibrations were suppressed by suspending the injectors from the fuel rail, providing no mechanical contact between the components. Also, they were able to attenuate the compression (at outlet) and ticking (at inlet) noises of the solenoid (up to 5 dB), using soft-landing and pulse-skipping control techniques, respectively. Figure 6: Schematics of (**a**) gasoline direct injection fuel system; (**b**) rail isolation and injector suspension [23]. Figures are reprinted with permission from publisher. [PERSON] and [PERSON] [24] experimentally and theoretically predicted the generated noise and vibration in the piston-rack assembly of a single-cylinder motorbike engine.