New High Quality Diesel Nozzle DLLA149P2216 for Injection Nozzle Diesel Engine Parts

Abstract
The surface properties of fuel injector nozzles are critical to ensuring precise fuel delivery, wear resistance, and long-term sealing performance under high-pressure operation. Plasma nitriding, as an advanced surface modification technique, offers significant improvements in surface hardness, fatigue resistance, and corrosion protection by forming nitrogen-enriched compound layers. This study investigates the influence of plasma nitriding parameters on the microhardness, microstructure, and sealing performance of injector nozzle materials, combining experimental testing and simulation analysis.

1. Introduction
In modern diesel and gasoline direct injection systems, injector nozzles are exposed to cyclic high-pressure fuel impact and thermal loads up to 200 MPa and 300°C. These harsh conditions can cause surface wear, deformation, and leakage at the sealing interface. Conventional heat treatments have limited effectiveness in improving the hardness-depth profile and maintaining dimensional precision. Plasma nitriding, due to its low processing temperature and strong diffusion capability, provides a promising approach to enhancing both wear resistance and sealing reliability without distorting the nozzle geometry.

2. Plasma Nitriding Process and Mechanism
Plasma nitriding introduces active nitrogen ions into the metal surface through glow discharge in a low-pressure nitrogen–hydrogen atmosphere. The process forms a compound layer composed mainly of ε-Fe₂–₃N and γ’-Fe₄N, followed by a diffusion zone enriched with interstitial nitrogen. This dual-layer structure enhances surface hardness and fatigue resistance while maintaining core ductility.

• Processing Conditions: Treatment temperatures between 480–540°C and durations of 6–10 hours were found to produce an optimal balance between hardness and residual stress.

• Microstructural Features: Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses confirmed a uniform nitride layer thickness of 10–20 μm and refined grain boundaries that inhibit crack initiation.

3. Influence on Surface Hardness and Sealing Performance
The plasma-nitrided injector nozzles exhibited substantial improvement in key surface properties:

• Surface Hardness: Microhardness increased from 320 HV to over 950 HV, representing nearly a threefold enhancement. This improvement reduces wear at the needle–seat interface and extends service life.

• Sealing Performance: The enhanced hardness and smoother surface reduce micro-leakage and maintain better contact conformity between the nozzle seat and the needle valve. Leakage testing under 180 MPa fuel pressure showed a 40% reduction in leakage rate compared with untreated samples.

• Thermal Stability: Hardness retention above 80% was observed after thermal exposure at 300°C for 20 hours, confirming strong diffusion bonding and stable nitride formation.

4. Conclusion
Plasma nitriding treatment significantly enhances the surface hardness and sealing performance of fuel injector nozzles by creating a dense, nitrogen-rich compound layer with excellent wear and thermal stability. The process effectively balances surface strengthening and structural integrity, ensuring reliable sealing under ultra-high-pressure fuel injection conditions. Future work should focus on optimizing plasma parameters, such as bias voltage and gas composition, to achieve gradient nitriding effects and further extend nozzle durability for next-generation high-efficiency combustion systems.