Application of Helium Mass Spectrometry Leak Detectors in the Production of Direct Injection Engines

Helium detection, as a new leak detection process, can effectively improve the quality of engines at the factory and reduce the hidden dangers of leaks. Compared to traditional air-tightness testing, helium testing has incomparable advantages, overcoming the issues of safety, equipment composition, and long cycle times associated with fuel detection.

After the introduction of fuel direct injection technology into gasoline engines, the assembly quality of the high-pressure fuel rail system, the core part of the engine, directly affects the vehicle performance and user experience. The two sealing detection technologies after the assembly of the high-pressure fuel rail system of direct injection engines are applied in the production project, listing the cases and characteristics of the two sealing detection technologies, which have a certain reference value for the selection of sealing detection process in the engine assembly process. The high-pressure fuel rail system is the most critical system of the direct injection engine. Unlike the previous mixing of oil and gas in the intake manifold, which is then sucked into the engine combustion chamber by negative pressure, the direct injection engine sprays fuel directly into the combustion chamber through a high-pressure fuel injector. Through the special structure of the piston head, the fuel and intake air are fully mixed in the combustion chamber to achieve higher combustion efficiency.

The high-pressure fuel rail system is a sealed space. Under normal operation, the pressure in the high-pressure fuel rail system reaches 150-400bar (ordinary fuel rail 3-6bar), and the entire system is under high pressure. This requires a high level of sealing for the fuel system, and even a slight leak point can cause a very serious oil seepage phenomenon, which cannot form high pressure and is prone to safety and quality accidents. Daarom, each main engine factory strictly controls the assembly process of the oil rail system during the production of direct injection engines, and uses different detection methods to detect and monitor the sealing of the high-pressure fuel rail system to prevent risks. Byvoorbeeld, when measuring leaks under the normal working pressure of the high-pressure fuel rail system, the resolution of the leak detector needs to reach 10-4cc/s. The commonly used detection methods are helium detection and fuel detection under the simulated working state of the engine.

A company’s third-generation engine project, during the production process, compared the two methods of fuel detection and helium detection, and finally put helium detection into actual production.

Helium Mass Spectrometry Leak Detector – Helium Detection

Helium detection is a technology that uses a helium mass spectrometry leak detector to detect leaks with helium gas as a trace gas. The main principle is to ionize gas molecules with a mass spectrometer, deflect the charged ions under the action of a magnetic field, and different ions with different mass-to-charge ratios have different deflection radii. By filtering and measuring the collected helium ions, the detection purpose is achieved.

Because the content of helium in the air is very small (about 5.2 parts per million), it is an inert gas with small molecules, ligte gewig, and strong penetration. Op dieselfde tyd, due to its non-reactive chemical properties, non-polluting to the workpiece, and safe operation, helium detection technology is widely used in the field of parts manufacturing. Through research on major domestic main engine manufacturers, it is found that the quality after the assembly of the high-pressure oil rail is guaranteed by the suction gun helium detection method.

The suction gun helium detection equipment mainly consists of four parts:

(1) Vacuum pumping system – to vacuum and evacuate the pipeline system to keep the gas composition in the pipeline clean;

(2) Helium supply system – to ensure the supply of helium during the detection process;

(3) Helium detector, suction gun – the core equipment of helium detection, to detect the leakage points of the system;

(4) Exhaust system – to promptly evacuate the leaked helium in the helium detection area and the residual helium in the pipeline to ensure the cleanliness of the area and prevent interference.

The helium detection process is as follows:

(1) Vacuum pumping – to vacuum the inflation pipeline, mainly to exclude the air in the inflation pipeline to ensure that the gas filled is helium;

(2) Low pressure helium inflation – as long as it can open the low-pressure inlet of the high-pressure oil pump at the low-pressure end of the high-pressure oil pump, and smoothly inflate helium into the oil rail, according to the characteristics of the oil pump, generally between 1-2 bar;

(3) Detecting large leaks – to detect whether there are large leakage points in the system, to prevent a large amount of helium leakage affecting the test environment and affecting normal production; the common practice is to detect the pressure drop change of the inflation system within a certain period of time;

(4) Inflation of helium gas at test pressure – to inflate the test system with the set pressure of helium;

(5) Leak detection – to use the suction gun to detect the installation points;

(6) Helium evacuation of the test system – this step has two functions, one is to eliminate the influence of residual helium, to evacuate the helium in the test pipeline to prevent residual helium leakage in the pipeline, affecting the test, and the second is to eliminate safety hazards, because the inflation pressure is generally around 8 bar, and there is an impact when directly plugging the block;

(7) End – the workpiece test is over, and the next leak detection cycle is carried out.

The logical sequence of the helium detection process is shown in the figure. According to the helium test process and research, combined with the characteristics of the assembly line of a company’s third-generation engine project, to achieve the requirements of low investment, low maintenance cost, and effective error prevention, a manual leak detection method is finally adopted on the existing production line process layout. Anhui Nuoyi NHJ series helium mass spectrometry leak detectors have high precision, fast response, high safety, wide adaptability, and are compact and portable, which have unique advantages in both leak point positioning and leak test applications. Welcome to exchange on helium mass spectrometry leak detection technology!