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The autoignition temperature or self-ignition temperature, often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature) and formerly also known as kindling point, of a substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark. [1]
Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion , this exothermic reaction produces heat that can be transformed into work in a heat engine .
"Rollover" or tongues of fire appear (known as "angel fingers" to firefighters) as gases reach their auto-ignition temperatures. There is a rapid build-up (or "spike") in temperature due to the compound effect of rapidly burning (i.e., deflagrating) gases and the thermal cycle they produce. This is generally the best indication of a flashover. [2]
Ignition occurs as the temperature of the fuel/air mixture is taken over its autoignition temperature, due to heat generated by the compression of the air during the compression stroke. The vast majority of compression ignition engines are diesels in which the fuel is mixed with the air after the air has reached ignition temperature.
Auto-ignition can be mitigated by using fuels with high auto-ignition resistance (octane rating), however it still puts an upper bound on the allowable peak cylinder temperature. The thermodynamic limits assume that the engine is operating under ideal conditions: a frictionless world, ideal gases, perfect insulators, and operation for infinite ...
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The auto ignition point of blast furnace gas is approximate 630–650 °C (1,166–1,202 °F) and it has a lower explosive limit (LEL) of 27% and an upper explosive limit (UEL) of 75% in an air-gas mixture at normal temperature and pressure. The high concentration of carbon monoxide makes the gas hazardous.
A cold start can be difficult for an engine due to higher viscosity of oil and fuel in cold temperatures. Generally speaking, diesel engines have more difficulty starting at low outside temperatures than gasoline engines, and electric engines have the most problems. Diesel engines do not use spark plugs to ignite the air fuel mixture and rely ...