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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]
Flashover occurs when the majority of the exposed surfaces in a space are heated to their autoignition temperature and emit flammable gases (see also flash point). Flashover normally occurs at 500 °C (932 °F) or 590 °C (1,100 °F) for ordinary combustibles and an incident heat flux at floor level of 20 kilowatts per square metre (2.5 hp/sq ft).
The high compression ratio in the auxiliary combustion chamber causes the auto-ignition of the homogeneous lean air-fuel mixture therein (no spark plug required); the burnt gas bursts - through some "transfer ports", just before the TDC - into the main combustion chamber triggering its auto-ignition. The engine needs not be structurally stronger.
The maximum temperature of about 2,800 °C (5,100 °F) is achieved with an exact stoichiometric mixture, about 700 °C (1,300 °F) hotter than a hydrogen flame in air. [ 7 ] [ 8 ] [ 9 ] When either of the gases are mixed in excess of this ratio, or when mixed with an inert gas like nitrogen, the heat must spread throughout a greater quantity of ...
The reduced engine speeds allow more time for autoignition chemistry to complete thus promoting the possibility of pre-ignition and so called "mega-knock". Under these circumstances, there is still significant debate as to the sources of the pre-ignition event. [3] Pre-ignition and engine knock both sharply increase combustion chamber temperatures.
Practically speaking the intake air mass temperature must also be reduced to prevent premature ignition in a petrol fueled engine; hence, an intercooler is used to remove some energy as heat and so reduce the intake temperature. Such a scheme both increases the engine's efficiency and power.
Heat-producing elements can be designed to limit their maximum temperature below the autoignition temperature of the material involved. Controls can be fitted to detect dangerous concentrations of hazardous gas, or failure of countermeasures. Upon detection, appropriate action is automatically taken, such as removing power, or providing ...
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 ...