Why is fuel pressure inconsistent in traffic?

High temperatures trigger multiple attenuation effects. During urban traffic congestion, the engine compartment temperature can reach 75°C (45°C during normal driving), and when the Fuel temperature rises to 60°C, the viscosity decreases by 0.68cSt, resulting in a 27% increase in internal leakage of the Fuel Pump. SAE experiments have proved that for every 10°C increase in temperature, the volumetric efficiency of vane pumps decreases by 4%, the flow fluctuation range reaches ±15 L/h (normal ±3 L/h), and the rail pressure deteriorates from 58.5±1 psi to 48±7 psi. In 2023, the Los Angeles Department of Transportation reported that the abnormal rate of fuel pressure on days with a temperature of 38℃ soared to 350% of the normal value.

Voltage fluctuations directly suppress the pump’s performance. Under start-stop conditions, the battery voltage drops to 11.2V (standard 13.5V), and the oil pump’s rotational speed decreases by 40% to 4200 rpm. Data records show that in the brake-start cycle, each time the voltage drop exceeds 0.9V for 5 seconds, the time required for rail pressure recovery is delayed from 1.2 seconds to 3.8 seconds, resulting in 23% of transient fuel supply shortage. Data analysis of the BMW 3 Series infotainment system shows that frequent starts and stops cause the Fuel Pump to be below the rated working voltage for a proportion of 31%.

The vapor lock effect intensifies under low-speed conditions. When the oil temperature is 50℃, the saturated vapor pressure of the fuel rises to 65 kPa. When the oil level is below 30% capacity and the volume concentration of gasoline vapor exceeds 12%, the probability of cavitation formation at the suction end of the oil pump increases by 67%. In the actual test of the Renault Clio, after waiting for 3 minutes after parking, the flow rate dropped sharply by 53%, and the voltage fluctuation of the oxygen sensor exceeded 0.45V. A 2022 study by the University of Tokyo confirmed that the combination of 30% fuel level and high-temperature environment leads to an 18-fold increase in the rate of urban driving fires.

Heat accumulation triggers a vicious cycle. When congestion occurs, the heat dissipation efficiency drops by 72%, and the temperature of the Fuel Pump motor rises from 85°C to 120°C (with a working limit of 130°C). The increase in copper loss leads to a 35% decline in efficiency. Infrared thermal imaging shows that after 30 consecutive minutes of idling, the local hot spot of the pump body reaches 142°C, the demagnetization rate of the magnet increases by 5 times, and the deviation of the pressure output linearity expands to ±9%.

The intelligent control system partially alleviates fluctuations. Bosch’s new generation Fuel Pump integrates a PWM duty cycle adaptive algorithm, which automatically increases the base speed compensation by 30% when 67 voltage fluctuations are detected within 12 seconds. Actual measurements show that the Audi A4 equipped with this system has its pressure fluctuation range compressed to 58±3 psi (±12 psi for the traditional system) during the evening rush hour in Shenzhen, and the air-fuel ratio control accuracy has been improved by 83%. The solution cost increases by approximately 800 yuan per set, but reduces the fuel injector cleaning cost by 80%.

The oil circuit optimization engineering plan has been verified to be effective. Installing a pressure storage tank to provide 0.5L of emergency fuel (with a release rate of 300ml/s) has extended the pressure reduction time buffer by 600ms. The comparison test of the Mercedes-Benz E-Class shows that after optimization, the pressure valley value under the stop-and-go condition has risen from 38psi to 47psi, and the stalling accident has decreased by 92%. It is also recommended to maintain an oil content of ≥50% and use ISO 22867-certified low permeability pipelines, which can compress the steam generation by 70%.

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