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Because pressure and temperature are strongly linked, knock can also be attenuated by controlling peak combustion chamber temperatures by compression ratio reduction, exhaust gas recirculation, appropriate calibration of the engine's ignition timing schedule, and careful design of the engine's combustion chambers and cooling system as well as ...
Pressure in cylinder pattern in dependence on ignition timing: (a) - misfire, (b) too soon, (c) optimal, (d) too late. In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.
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.
There are pressure losses due to duct wall friction in all ducts but an afterburner has additional losses caused by flameholders and fuel supply tubes. The fundamental pressure loss, that due to burning, increases with Mn at entry to burning zone and with the amount of fuel burned in terms of the increase in temperature in the afterburner. [98]
Likewise, a stronger driving of a combustion instability happens when the heat is released at a higher pressure. But while high heat release and high pressure coincide (roughly) throughout the combustion chamber in an ICE, they coincide at a particular region or regions during a combustion instability.
When the flame moves backward it may also be called a "pop-back". A backfire can be caused either by ignition that happens with an exhaust valve open or unburnt fuel making its way into the hot exhaust system. A visible flame may momentarily shoot out of the exhaust pipe. A backfire is often a sign that the engine is improperly tuned.
These engines can either be full-time lean-burn, where the engine runs with a weak air–fuel mixture regardless of load and engine speed, or part-time lean-burn (also known as "lean mix" or "mixed lean"), where the engine runs lean only during low load and at high engine speeds, reverting to a stoichiometric air–fuel mixture in other cases.
Cooling is required to remove excessive heat—high temperature can cause engine failure, usually from wear (due to high-temperature-induced failure of lubrication), cracking or warping. Two most common forms of engine cooling are air-cooled and water-cooled. Most modern automotive engines are both water and air-cooled, as the water/liquid ...