The pre-injection operation can eliminate the transient thermal shock caused by dry running. Tests in the Bosch laboratory show that when the Fuel Pump is started for the first time without fuel infiltration, the temperature rise of the motor armature will exceed 150℃ within 0.8 seconds, far exceeding the heat resistance limit of the permanent magnet (120℃). This will lead to an 18% increase in the demagnetization rate of the magnetic steel and a permanent 5.2% attenuation in the torque output. The pre-injection program of the Porsche 911 (992 model) can establish an oil pressure of 3.2bar 0.3 seconds before ignition, avoiding the peak instantaneous temperature rise caused by dry friction in the pump chamber.
The cavitation protection effect significantly enhances reliability. General Motors’ research has confirmed that insufficient pre-injection causes residual bubbles in the pump cavity to account for more than 15% of the volume. When the blades operate at 6000rpm, a local compression burst of 250-290 kpa will be formed. Continuous cavitation for 30 seconds causes honeycomb-shaped erosion pits with a diameter of ≥0.2mm to appear on the surface of the impeller, and the flow efficiency attenuation reaches 13%. The solution of the Renault-Nissan Alliance is to perform two 0.5-second interval pulse pre-injections, reducing the cavitation probability from 28% to less than 4%.
The lubrication establishment process shortens the wear cycle. Experimental data show that when a plunger pump without pre-injection is cold-started, only a trace amount of grease is used to lubricate the plunger and the cylinder block, and the friction coefficient is as high as 0.11 in the initial 30 seconds (only 0.02 in the normal oil film lubrication state). The intelligent pre-injection system of the BMW B58 engine can increase the oil delivery volume to 2.3L/min in an environment of -30℃ and reduce the wear rate of the CAM bearing to 0.4μm/ 1,000 kilometers (up to 1.6μm without pre-injection).
The pressure stabilization time affects the injection accuracy. The actual measurement of Delphi’s fuel system shows that the standard deviation of fuel pressure fluctuation in the unfueled circuit from 0 to 300ms before startup reaches ±1.8bar, directly resulting in an error rate of more than ±25% in the first fuel injection volume. The Volkswagen EA888 Gen4 engine that performs a 2-second pre-injection can stabilize the high-pressure fuel rail pressure to 150bar±0.8% within 50ms, ensuring that the λ value is controlled within the ideal range of the median value of 1.0±0.05.
The optimization of maintenance costs reflects economic value. Fiat Group’s North American after-sales data shows that the average lifespan of fuel pumps in vehicles that adhere to full pre-injection is 150,000 kilometers, which is 114% longer than that of owners who start them randomly (an average of 70,000 kilometers). Based on the Bosch oil pump assembly of 220, the operating cost per thousand kilometers has dropped to 1.47 (compared with 3.14). If the reduced towing costs (150 per time) and labor costs (95 per hour) are taken into account, 84 can be saved over a 24-month period.
Intelligent pre-injection technology enables precise control. The pre-injection module of the Mercedes-Benz M279 engine integrates a pressure sensor and a temperature compensation algorithm. It automatically adjusts the pre-injection duration based on the fuel viscosity (0.8 seconds at 0℃ and 1.5 seconds at -20℃), reducing the start-up wear by 73%. In the 2023 Le Mans Endurance race, the fuel pump efficiency retention rate of the racing cars adopting this technology still reached 97.2% after completing the 24-hour race course.