What Are the Influencing Factors of the Optimal Ignition Timing Advance Angle?
2 Answers
The most significant factor affecting the ignition timing advance angle is engine speed. As the speed increases, the time required to rotate through the same angle decreases, necessitating a larger advance angle to achieve the corresponding advance time. Theoretically, the minimum ignition advance angle is 0 degrees, but to prevent igniting the air-fuel mixture during the power stroke (which would result in power loss), it is typically set above 5 degrees—this is also the angle required for starting speed. The maximum ignition advance angle should not be excessively large, generally not exceeding 60 degrees; otherwise, issues such as vibration and temperature rise will become prominent, and efficiency will decline. In practice, the speed is limited by the crankshaft structure. The effects of non-optimal ignition timing include: 1. Over-advanced ignition: Causes knocking, obstructs piston upward movement, reduces efficiency, and increases thermal load, mechanical load, noise, and vibration. 2. Excessively delayed ignition: Makes gas power generation difficult, increases fuel consumption, reduces efficiency, and results in louder exhaust noise. Both over-advanced and delayed ignition will hinder speed improvement. The optimal ignition angle is influenced by the following factors: 1. Cylinder temperature and pressure: Higher values lead to faster combustion, requiring a smaller ignition advance angle. Factors affecting cylinder temperature and pressure include engine compression ratio, ambient temperature, cylinder temperature, and load. 2. Gasoline octane rating: Higher octane ratings indicate stronger anti-knock performance, allowing for a larger ignition advance angle.
When I used to tune engines, I found that the ignition timing parameter was particularly sensitive. The most direct factor is engine speed—the higher the RPM, the earlier the ignition needs to be to allow enough time for the air-fuel mixture to burn. Then there's the load factor; when climbing a hill with reduced air intake, you actually need to retard the ignition to prevent knocking. The octane rating of the gasoline is also crucial—using 95-octane fuel allows for a few degrees more advanced ignition compared to 92-octane. If the knock sensor detects abnormal vibrations, it will immediately instruct the ECU to retard the ignition timing. In high-altitude areas with thin air, like during my tests in Tibet, I had to rewrite the ECU calibration specifically—for every 1000 meters of elevation gain, the ignition timing needed adjustment by about 1.5 degrees. The coolant temperature sensor also requires attention; during cold starts, when the coolant is still cold, the ignition timing needs to be advanced by about 5 degrees more than in a warmed-up state to ensure stability.
