What Does Engine Idle Speed Refer To?

[SanAdrian]

Idle speed refers to an operating state of the engine where there is no external power output. It is one of the five basic operating conditions of an engine, which include cold start, idle, acceleration, light load, medium load, and heavy load. The purpose of idle speed is to overcome the internal resistance of the engine and maintain a non-stalling state. The following are the impacts of idle performance on gasoline engines: 1. Fuel Economy: Since engines frequently operate at idle, statistics show that urban vehicles consume about 30% of their fuel during idle conditions. Therefore, reducing fuel consumption during idle is crucial, which is also a requirement for idle control. The primary measure to reduce idle fuel consumption is lowering the idle speed. 2. Emissions: During idle conditions, gasoline engines have a high amount of residual exhaust gases in the cylinders. To ensure stable combustion, the air-fuel mixture needs to be enriched, leading to incomplete combustion and the production of harmful emissions such as CO and HC. Experiments have shown that the lower the idle speed, the more pronounced the dilution effect of exhaust gases, further increasing the concentration of CO and HC emissions. Thus, increasing idle speed is beneficial for reducing CO and HC emissions.