Principles of Combustion Analysis

Much of the material in Sections 813, 814, 815 and 816 has been extracted from materials provided by Rotating and Reciprocating Specialists.

The purpose of this analysis is to:
• Optimize fuel consumption, and
• Detect mechanical problems before they become serious enough to cause significant damage to the machine.
Typical combustion patterns are depicted on Figure 800-5 and may be defined as follows:
1. Normal Combustion—Ignition timed correctly, proper air/fuel mixture, no malfunctions.
2. No Combustion (Dead miss)—Cause: ignition or mixture, also water in cylinder.
3. Early Combustion—Cause: ignition timing, mixture, or temperature.
4. Late Combustion—Cause: late ignition, mixture (rich or lean) or water in cylinder.
– Terminal pressure high—rich mixture
– Terminal pressure low—lean mixture
5. Detonation (too rapid combustion rate—uncontrolled)—Cause: mixture, excess load. Rich mixture tends to detonate.
6. Pre-ignition (auto-ignition)—Cause: hot spot, carbon or foreign matter in the combustion chamber, excess cylinder temperature, presence of heavy hydrocarbons.

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