High temperatures cause significant changes in the physical properties of fuel, directly weakening the fuel transmission efficiency. For every 20℃ increase in temperature, the volume expansion rate of gasoline reaches 1.15%, its density decreases by 3.8%, and the energy contained in the same volume of fuel reduces by approximately 2.5%. This change forces the Fuel Pump to deliver 10%-15% more volumetric flow rate to maintain the mass flow rate required by the engine. At this time, the median value of the system pressure can drop by 0.4 bar (the benchmark value is 3.0 bar), and the pressure fluctuation range increases to 1.8 times the normal state. The 2021 SAE J1681 test standard confirmed that the gasoline viscosity dropped to 0.5mm²/s at 80 ° C (0.7mm²/s at 20 ° C), and the deterioration of dynamic viscosity caused a 15% loss in the energy transmission efficiency of the impeller.
The functional decline of the internal components of the Fuel Pump under thermal load intensifies the risk of pressure loss. The magnetic flux of permanent magnet motors decays by 5% to 7% at 80℃, and the increase in rotor resistance causes the rotational speed to drop by 300 to 500rpm. For every 10℃ increase in temperature of the armature winding, the resistance increases by 4%, and under the same voltage, the output power decreases by up to 12%. Data from the Bosch Laboratory in Germany shows that the contact resistance between carbon brushes and commutators increases by 50% in a hot environment, causing the probability of voltage drop deviation to soar from 3% at room temperature to 28%. In 2019, General Motors recalled 150,000 Sierra HD trucks. The fundamental reason was that the armature of the high-temperature fuel pump overheated and deformed, and the peak oil pressure dropped from 3.2 bar to 1.9 bar.
The mechanical fit tolerance deviates from the design threshold under the effect of thermal expansion. The thermal expansion coefficient of the aluminum alloy pump casing reaches 23×10⁻⁶/℃, which is 62% higher than that of the stainless steel impeller. At 80℃, the radial expansion of the casing exceeds that of the impeller by 0.12mm. This difference causes the end face clearance of the impeller to expand to 0.3mm (design value 0.15mm±0.03mm), the volumetric efficiency drops sharply by 25%, and the pressure establishment rate slows down by 40%. The solution for the Porsche 911 (992 model) is to use thermal expansion matching composite materials, which extends the operating temperature range to -40℃ to 120℃ and keeps the oil pressure fluctuation within ±0.15 bar.
The probability of fuel evaporation and vapor lock increases exponentially with temperature. When the temperature exceeds 45℃, the vapor pressure of gasoline breaks through 75kPa (about 55kPa at 20℃), and the release rate of dissolved air increases by 2.3 times. When the local temperature of the oil pipe reaches 55℃, the occurrence rate of cavitation increases to 38%, causing the system pressure to drop instantaneously by more than 0.8 bar. Statistics on vehicle malfunctions in the Middle East in 2023 show that the number of oil pump failure cases increased by 210% during the high-temperature season, among which 67% were accompanied by abnormal valleys below 2.0 bar recorded by pressure sensors. Modern solutions include installing temperature-pressure coupled sensors on the fuel rail to dynamically adjust the PWM duty cycle of the fuel pump, improving control accuracy to ±2% and reducing oil pressure offset to the 0.1 bar range.
The thermal aging of elastic seals accelerates, causing microscopic leakage. The hardness of nitrile rubber sealing rings decreases by 15 degrees (IRHD) in an environment of 100℃, and the compression set rate rises to 20% (only 8% at 70℃). The leakage rate of the sealing surface of the oil pump outlet valve increases to 0.8L/min at high temperatures (standard value ≤0.3L/min), and the system needs to increase the flow compensation by an additional 18% to maintain the target pressure. Fluid dynamics simulation proves that for every 10℃ increase in temperature, the molecular permeability at the sealing interface increases by 2.7 times and the pressure relief rate increases by 1.9 times. The response plan adopts fluororubber material (with an upper temperature resistance limit of 175℃), combined with laser welding shell technology, and the leakage rate is controlled at ≤0.05%.
