Diesel Generator Running-In Procedures

1. Introduction

The running-in test is an essential procedure for diesel generators to ensure that moving components, particularly the piston skirt and cylinder liner, piston rings and cylinder liner, and journal and bearings, achieve uniform contact and optimal fit clearance. This process prevents early excessive wear, scratches, or damage resulting from machining imperfections and installation quality issues. Running-in enhances the durability, corrosion resistance, and operational reliability of generator components by conditioning friction surfaces and eliminating geometric deviations from manufacturing.

Running-in tests are categorized into two types:

• Cold Running-In: The generator is driven by external power sources, such as an electric motor or dynamometer.
• Hot Running-In: The diesel generator operates under its own power in a heated state.

This document outlines the purpose, procedures, and specifications for both cold and hot running-in tests, providing a standardized guide for implementation.

2. Purpose of Running-In Tests

The running-in process serves several critical functions:

• Surface Conditioning: Even with precision machining, component surfaces remain microscopically rough and exhibit macroscopic imperfections (e.g., taper, ovality, positional tolerances). Running-in smooths these surfaces, increasing the actual contact area from an initial 30%-50% of the nominal area to a higher, stable level.
• Wear Reduction: Before running-in, concentrated loads at contact points can cause overheating, lubrication film breakdown, and potential seizure or bonding. Running-in gradually expands the contact area, reducing wear rates to a normal, stable stage.
• Fault Prevention: Improper speed or load during initial operation can lead to severe friction, metal tearing, or surface damage. Controlled running-in mitigates these risks.
• Quality Assurance: Running-in, combined with subsequent adjustments, verifies the quality and performance of newly installed or overhauled generators, ensuring compliance with technical standards.

Running-in is an indispensable step in the installation and major overhaul of diesel generator sets, requiring operators and repair personnel to master its implementation.

3. Theoretical Basis of Running-In

Running-in is a complex process involving mechanical, physical, and chemical interactions that transition friction surface properties from their initial state to a stable operational state. It can be understood in both narrow and broad contexts:

1. Microscopic Roughness: Regardless of machining precision, surfaces are microscopically uneven, leading to limited initial contact area (typically 30%-50% of nominal).
2. Load Distribution: Small contact areas result in high localized pressure, heat generation, and potential lubrication failure, risking surface damage. Running-in mitigates this by progressively increasing contact area.
3. Surface Interaction: Initial protrusions on moving surfaces interlock and wear down. Inappropriate speed or load can cause severe friction or metal tearing, which running-in prevents through controlled conditions.

4. Types of Running-In Tests

4.1 Cold Running-In

• Definition: The diesel generator is driven by an external power source (e.g., electric motor, dynamometer) without combustion.
• Purpose: Conditions the crank-connecting rod system, valve mechanism, and other clearance-fit components.
• Implementation: Typically conducted by manufacturers or well-equipped repair facilities due to the need for specialized equipment.
• Procedure: Detailed steps are illustrated in Figure 3 (refer to accompanying diagrams).
• Duration: Varies based on specifications, typically a few hours.

4.2 Hot Running-In

• Definition: The diesel generator operates under its own power in a heated state.
• Purpose: Verifies operational integrity, adjusts performance, and ensures economic and dynamic efficiency through no-load and loaded tests.
• Implementation: Suitable for general users and performed after installation and initial checks.
• Procedure: Detailed steps are illustrated in Figure 4 (refer to accompanying diagrams).

For users without cold running-in capabilities, hot running-in can be performed directly after installation or overhaul.

5. Running-In Specifications

Running-in specifications vary based on the components involved and the desired outcomes. Below are the standardized stages:

5.1 Microscopic Geometric Shape Running-In

• Components: Valve mechanisms, gear trains (point or line contact friction pairs with high stress and splash lubrication).
• Conditions: Low to medium speeds, no load or light load (≤50% of rated load per speed stage).
• Duration: A few minutes to 6 hours.
• Objective: Smooths microscopic surface roughness, critical for component longevity.

5.2 Macroscopic Geometric Shape Running-In

• Components: Crank-connecting rod mechanism, journal and bearings (requiring both microscopic and macroscopic conditioning).
• Conditions: Medium to high speeds (up to rated speed), medium to full load.
• Duration: Several hours to dozens of hours.
• Objective: Corrects macroscopic geometric deviations, with journal-bearing running-in being the most time-intensive.

5.3 Comprehensive Running-In

• Aplicaciones: Complex performance tests, comparative performance trials, and developmental testing.
• Conditions: Combines microscopic and macroscopic running-in, with later stages at medium to high speeds (up to rated speed) and full load.
• Duration: 20-40 hours.
• Objective: Stabilizes mechanical loss power and optimizes performance indicators.

6. Hot Running-In Procedure

Hot running-in consists of two phases: no-load and loaded tests.

6.1 Preparation

Before initiating hot running-in:

• Install all assemblies, accessories, and instrumentation.
• Fill with fuel, engine oil, and cooling water.
• Adjust critical parameters:
  • Valve clearance
  • Fan belt tension
  • Oil pressure
  • Injection pressure
  • Fuel supply timing and quantity
  • Cylinder fuel supply uniformity
• Ensure the generator is in optimal working condition.

6.2 No-Load Test

• Purpose: Confirms the generator operates without damage.
• Specification (1500 rpm Example): Refer to Table 5-3 for stages, speeds, and durations. For other rated speeds, adjust speeds while maintaining the same stages and times.
• Duration: Typically a few hours, depending on the specification.

6.3 Loaded Test

• Purpose: Evaluates the quality of a newly installed or overhauled generator against technical standards.
• Specification (1500 rpm Example): Refer to Table 5-4 for stages, speeds, loads, and durations. For other rated speeds, adjust speeds while maintaining the same stages, loads, and times.
• Duration: Several hours, depending on load progression.

7 Post-Running-In Procedures

After completing the hot running-in test:

• Adjustments: Recheck and adjust valve clearance.
• Fasteners: Retighten bolts and nuts on main bearings, connecting rods, and cylinder heads.
• Oil Change: Replace engine oil promptly to remove contaminants.
• Component Replacement: If critical parts (e.g., pistons, Pasadores de pistón, Anillos de pistón, camisas de cilindro, connecting rod bearings) are replaced during running-in to address faults, repeat the running-in process.
• Performance Testing: Conduct power output and fuel consumption rate tests to accurately assess generator quality.

8 Special Considerations

• Skipping Cold Running-In: For new installations or major overhauls where cold running-in is not feasible, proceed directly to hot running-in.
• Quality Verification: Post-running-in tests (power and fuel consumption) are critical to confirm the generator meets operational standards.
• Operator Competency: Understanding and executing running-in procedures is a fundamental skill for diesel generator operators and repair personnel.

9 Conclusion

The running-in process is vital for ensuring the longevity, reliability, and optimal performance of diesel generators. By adhering to the outlined cold and hot running-in procedures and specifications, operators can mitigate early wear, enhance component durability, and verify generator quality. This document provides a comprehensive, standardized framework for implementing running-in tests, suitable for both technical documentation and practical application.