Autoignition temperature

Autoignition Temperature

The autoignition temperature is the lowest temperature at which a substance will spontaneously ignite in a normal atmosphere without an external source of ignition, such as a flame or spark. This property is crucial in understanding the flammability and combustion characteristics of various materials, especially in the context of chemical engineering, fire safety, and automotive engineering.

Definition

Autoignition temperature is defined as the minimum temperature required to initiate or cause self-sustained combustion of a material in the absence of a spark or flame. It is a critical parameter in the design and operation of equipment that handles flammable substances.

Factors Affecting Autoignition Temperature

Several factors can influence the autoignition temperature of a substance:

• Pressure: Increasing the pressure generally lowers the autoignition temperature.
• Concentration: The concentration of the substance in the air can affect its autoignition temperature.
• Presence of Catalysts: Certain materials can act as catalysts, lowering the autoignition temperature.
• Humidity: The presence of moisture can influence the autoignition temperature.

Measurement

The autoignition temperature is typically measured in a controlled laboratory setting using a test apparatus that can precisely control the temperature and environment. The substance is gradually heated until it ignites, and the temperature at which this occurs is recorded as the autoignition temperature.

Applications

Understanding the autoignition temperature of materials is essential in various fields:

• Fire Safety: Helps in assessing the fire risk of materials and designing fire prevention systems.
• Chemical Process Safety: Critical in the design of chemical reactors and storage facilities to prevent accidental ignition.
• Internal Combustion Engines: Knowledge of autoignition temperatures is used to prevent engine knocking and improve fuel efficiency.

Examples

Different substances have different autoignition temperatures. Here are a few examples:

• Hydrogen: Approximately 500 °C (932 °F)
• Gasoline: Approximately 280 °C (536 °F)
• Ethanol: Approximately 365 °C (689 °F)

See Also

• Flash Point
• Flammability Limit
• Combustion

References

• "Fire Protection Handbook," National Fire Protection Association.
• "Chemical Process Safety: Fundamentals with Applications," Daniel A. Crowl and Joseph F. Louvar.