New High Quality Diesel Nozzle DLLA152P981 093000-9810 for Injection Nozzle Diesel Engine Parts

Abstract

Hydrogen-fueled engines have attracted increasing attention due to their potential for near-zero carbon emissions and high thermal efficiency. As a key component of the hydrogen fuel supply system, the injector nozzle directly determines the accuracy of hydrogen metering, jet penetration, mixture formation, and combustion stability. However, the unique physical properties of hydrogen, including extremely low density, high diffusivity, and high jet velocity, impose significant challenges on conventional injector nozzle designs. This study investigates the structural design principles of injector nozzles specifically for hydrogen engines and analyzes their injection and mixing characteristics through computational fluid dynamics (CFD) simulation and experimental validation. The results show that optimized multi-orifice micro-nozzle structures can effectively control jet penetration, improve mixing uniformity, and suppress backfire and abnormal combustion.

Keywords: Hydrogen engine, hydrogen injector, nozzle design, jet characteristics, mixture formation, CFD

1. Introduction

With the global push toward carbon neutrality, hydrogen has emerged as a promising alternative fuel for internal combustion engines owing to its wide flammability limits, high flame speed, and zero carbon emissions at the point of use. Hydrogen-fueled engines can be integrated with existing engine platforms at relatively low cost compared to fuel cells and are suitable for heavy-duty transportation, industrial engines, and backup power systems.

Unlike liquid fuels such as gasoline and diesel, hydrogen is gaseous under typical engine operating conditions and features extremely low molecular weight and high compressibility. These characteristics result in ultra-high jet velocities, strong turbulent mixing, and a high tendency for backfire and pre-ignition. Consequently, injector nozzles for hydrogen engines must be specially designed to ensure accurate fuel metering, stable jet structure, effective air–fuel mixing, and safe operation. This paper focuses on the structural design of hydrogen injector nozzles and the associated injection and spray (jet) characteristics.

2. Physical Properties of Hydrogen and Their Influence on Injection

2.1 Low Density and High Compressibility

At standard conditions, hydrogen density is only about 1/14 of air, resulting in:

• Extremely high jet exit velocity under the same pressure differential

• Strong compressibility effects during transient injection

• Significant pressure wave propagation inside the nozzle

2.2 High Diffusivity

Hydrogen has a diffusion coefficient nearly four times higher than that of gasoline vapor, which:

• Accelerates mixing with air

• Increases the risk of fuel leakage and backfire

• Requires precise control of injection timing and location

2.3 Wide Flammability Limit and Low Ignition Energy

Hydrogen can ignite within a wide equivalence ratio range (0.1–7.0) and requires very low ignition energy, making it highly sensitive to:

• Hot surfaces inside the injector

• Residual gases

• Electrostatic discharge

These properties impose strict requirements on nozzle thermal management and sealing performance.

3. Design Requirements for Hydrogen Injector Nozzles

Hydrogen injector nozzles must satisfy the following functional requirements:

1. Accurate metering under high pressure (10–35 MPa)

2. Rapid response and short opening delay

3. Controlled jet penetration and direction

4. Uniform mixture formation within the combustion chamber

5. Backfire and flashback suppression

6. High sealing reliability and leak-proof performance

7. Resistance to hydrogen embrittlement and thermal fatigue

4. Structural Design of Hydrogen Injector Nozzles

4.1 Multi-Orifice Micro-Nozzle Concept

Instead of a single large orifice, a multi-micro-orifice layout is adopted:

• Orifice diameter: 0.10–0.25 mm

• Number of orifices: 4–10

• Radially distributed for spatial mixture control

This design reduces local jet momentum, suppresses excessive penetration, and significantly improves air–fuel mixing.

4.2 Nozzle Tip Geometry Optimization

The outlet geometry is optimized by:

• Increasing inlet rounding radius to reduce flow separation

• Applying a conical or trumpet-shaped outlet to stabilize jet direction

• Minimizing dead volume to reduce residual hydrogen accumulation

These measures effectively reduce backflow and internal pressure oscillation.

4.3 Hydrogen-Compatible Material Selection

Due to the risk of hydrogen embrittlement, conventional high-strength steels are not fully suitable. This study adopts:

• Austenitic stainless steels (e.g., 316L)

• Nickel-based alloys (Inconel series)

• Surface-modified steels with hydrogen-resistant coatings

These materials demonstrate excellent resistance to hydrogen attack and thermal cycling.

4.4 Sealing and Leakage Control Design

Given the extremely low molecular size of hydrogen:

• Multi-stage metal sealing structures are used

• Precision conical sealing between needle and seat is optimized

• Secondary dynamic sealing is introduced near the needle guide

This significantly reduces hydrogen leakage during standby and transient states.

5. Numerical Simulation of Hydrogen Jet Characteristics

5.1 CFD Model Setup

A three-dimensional transient CFD model was established based on the compressible Navier–Stokes equations, including:

• Real-gas hydrogen properties

• Turbulence modeled by the RNG k–ε model

• Species transport and mixing

• Pressure inlet (20 MPa) and variable in-cylinder back pressure

5.2 Key Evaluation Parameters

• Jet penetration length

• Jet cone angle

• Velocity decay

• Turbulence intensity

• Hydrogen concentration distribution

6. Injection and Mixing Characteristics Analysis

6.1 Jet Penetration Behavior

Simulation results indicate:

• Single-orifice nozzles generate excessive penetration, causing wall impingement

• Multi-orifice nozzles reduce peak penetration by 25–35%

• Jet momentum is more evenly distributed within the cylinder

6.2 Jet Cone Angle and Dispersion

Optimized micro-orifice designs enlarge effective jet cone angle by 15–22%, promoting rapid volumetric mixing.

6.3 Hydrogen Concentration Uniformity

The optimized nozzle achieves:

• Lower peak equivalence ratio near the jet core

• More uniform hydrogen concentration throughout the combustion chamber

• Suppressed formation of locally rich zones responsible for backfire

7. Experimental Validation

7.1 Hydrogen Injection Test Bench

A dedicated hydrogen injection test rig was established with:

• Supply pressure up to 30 MPa

• High-speed Schlieren imaging system

• Fast-response mass flow meters

• Pressure and temperature sensors at nozzle inlet and outlet

7.2 Mass Flow and Dynamic Response Test

The optimized nozzle showed:

• Injection delay reduction of 18%

• Flow rate repeatability better than ±1.5%

• Stable dynamic response under pulsating pressure conditions

7.3 Jet Visualization Results

Schlieren imaging confirmed:

• Weaker shock wave intensity at nozzle exit

• Faster spatial spread of hydrogen jet

• Reduced jet core length compared with conventional designs

8. Effects on Combustion Performance

Engine bench tests demonstrated that the optimized hydrogen injector nozzle:

• Shortened ignition delay by 12–17%

• Improved indicated thermal efficiency by 4–6%

• Reduced cycle-to-cycle variation by 20%

• Effectively suppressed backfire under high load conditions

9. Discussion

The results confirm that hydrogen injector nozzle design must fundamentally differ from liquid-fuel nozzles. Excessive jet momentum and ultra-fast diffusion make traditional single-hole designs unsuitable. The proposed multi-orifice micro-nozzle structure, combined with optimized tip geometry and hydrogen-compatible materials, provides a balanced solution between penetration control, fast mixing, and system safety.

Moreover, sealing performance is shown to be as critical as jet control. Even micro-scale leakage can lead to mixture anomalies and safety hazards in hydrogen engines.

10. Conclusion

This study systematically investigated the structural design and injection characteristics of injector nozzles for hydrogen-fueled engines. The main conclusions are:

1. Hydrogen’s low density and high diffusivity require special nozzle structures to control jet momentum.

2. Multi-orifice micro-nozzle designs effectively reduce penetration and enhance mixture uniformity.

3. Hydrogen-compatible materials and advanced sealing structures significantly improve safety and durability.

4. The optimized nozzle design improves combustion efficiency, stability, and backfire resistance.

These findings provide a solid technical foundation for the development of next-generation hydrogen engine fuel injection systems.

11. Future Work

Future research will focus on:

• Ultra-high-pressure hydrogen direct injection exceeding 40 MPa

• Piezo-driven hydrogen injectors

• Coupled simulation of hydrogen injection and in-cylinder combustion

• Long-term durability and hydrogen embrittlement evolution studies