The core mechanism for the significant noise reduction of fuel pumps in the submerged state lies in the dissipation of vibration energy due to the increase in medium density. Experimental data show that when the Fuel Pump is fully immersed in gasoline (with a density of approximately 737 kg/m³) for operation, the vibration acceleration of the shell attenuates from 12.3 m/s² in the air environment to 4.7 m/s², a decrease of 62%. According to the ISO 3744 acoustic power test standard, A centrifugal pump of the same power generates 72 dB(A) of noise in the air and reduces it to 56 dB(A) after immersion, which is equivalent to a reduction of the acoustic energy to 6.25% of the original value. This stems from the optimization of acoustic impedance matching at the interface between the fluid and the metal – the acoustic impedance rate of gasoline is approximately 1.34×10⁶ Pa·s/m (while that of air is only 415 Pa·s/m), converting over 99% of mechanical vibrations into thermal energy consumption.
The thermal management effect of the liquid medium suppresses the temperature-type noise source. Tests show that the winding of the dry-installed oil pump can reach 145℃ under continuous load (the coefficient of thermal expansion of metal is 23×10⁻⁶/℃), inducing micro-deformation of the shell and generating 8kHz high-frequency howling. In the immersion condition, the fuel carries away heat at a flow rate of 0.35 L/min, maintaining the coil below 85℃ and reducing the thermal noise component by 12dB. The engineering verification of the BMW F90 M5 in 2018 showed that in the spectral analysis of the immersion pump at 6500rpm, the peak sound pressure level in the 1500-5000Hz band decreased by 50%, directly contributing a 38% increase in the dynamic sound quality score within 0.8 seconds in the cabin.
Fluid encapsulation also eliminates the noise of cavitation blasting. The experimental report of the U.S. Department of Energy reveals that when the gasoline pressure is lower than the saturated vapor pressure (about 55kPa at 20℃), a group of bubbles with a diameter of 0.1-0.3mm will be produced at the oil inlet end of the dry pump, and a 130dB pulse sound will be released at the moment of collapse. The increase in liquid column pressure in the submerged environment (7.3kPa for every 10cm of tank depth) suppresses the probability of cavitation occurrence from 35% to less than 2%. A typical case is that in 2022, the McLaren F1 team built a 45mm deep oil layer into the fuel tank, which reduced the high-frequency abnormal noise during the turbo period by 92% and improved the lap time by 0.3 seconds.
The structural sound transmission path is effectively blocked in the liquid. Vibration tests conducted by the Fraunhofer Institute in Germany show that in dry installation, 60% of the mechanical vibration is directly transmitted to the fuel tank shell (the sound transmission efficiency of aluminum alloy is 63%), while in submerged systems, the vibration velocity of the shell is reduced from 1.8 mm/s to 0.5 mm/s through oil damping. In the actual measurement of the Audi e-tron electric vehicle platform, this optimization reduced the cabin noise PSD (power spectral density) by 35μPa²/Hz at the key frequency point of 250Hz. The economic efficiency of the project is equally significant: After eliminating the necessary 8-layer composite sound insulation cover for dry pumps, the cost per unit was reduced by $17.6, and the assembly time on the production line was shortened by 25 seconds per unit.