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An engine that runs too hot or too lean may produce an environment conducive to allowing unspent fuel to burn. An idle speed that is too fast can leave the engine with too much angular momentum upon shutdown, raising the chances that the engine can turn over and burn more fuel and lock itself into a cycle of continuous running.
Carbon deposits form a heat barrier and can be a contributing factor to pre-ignition. Other causes include: An overheated spark plug (too hot a heat range for the application). Glowing carbon deposits on a hot exhaust valve (which may mean the valve is running too hot because of poor seating, a weak valve spring or insufficient valve lash)
In an aircraft with a reciprocating fuel injected engine a hot start is a condition where an engine start is attempted after it has been run, achieved operating temperature, and then recently shut down. The engine is therefore "hot ", hence the terminology "hot start".
Internal-combustion engines burn fuel hotter than the melting temperature of engine materials, and hot enough to set fire to lubricants. Engine cooling removes energy fast enough to keep temperatures low so the engine can survive. [2] Some high-efficiency engines run without explicit cooling and with only incidental heat loss, a design called ...
The efficiency of ordinary heat engines also generally increases with operating temperature, and advanced structural materials that allow engines to operate at higher temperatures is an active area of research. Due to the other causes detailed below, practical engines have efficiencies far below the Carnot limit.
HCCI engines have a long history, even though HCCI has not been as widely implemented as spark ignition or diesel injection. It is essentially an Otto combustion cycle. HCCI was popular before electronic spark ignition was used. One example is the hot-bulb engine which used a hot vaporization chamber to help mix fuel with air. The extra heat ...
A flooded engine is an internal combustion engine that has been fed an excessively rich air-fuel mixture that cannot be ignited. [1] This is caused by the mixture exceeding the upper explosive limit for the particular fuel. An engine in this condition will not start until the excessively rich mixture has been cleared. [2]
Modern engines run hot, that is, over 80 °C (180 °F), in order to run more efficiently and to reduce the emission of pollutants. While the thermostat is closed, there is no flow of coolant in the radiator loop, and coolant water is instead redirected through the engine, allowing it to warm up rapidly while also avoiding hot spots.