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The objective of knock control strategies is to attempt to optimize the trade-off between protecting the engine from damaging knock events and maximizing the engine's output torque. Knock events are an independent random process. [8] It is impossible to design knock controllers in a deterministic platform. A single time history simulation or ...
Cool flames may contribute to engine knock – the undesirable, erratic, and noisy combustion of low-octane fuels in internal combustion engines. [2] In a normal spark-ignition engine, the hot premixed flame front travels smoothly in the combustion chamber from the spark plug, compressing the fuel/air mixture ahead.
The first production engine with a variable compression ratio was introduced in 2019. Variable compression ratio is a technology to adjust the compression ratio of an internal combustion engine while the engine is in operation. This is done to increase fuel efficiency while under varying loads. Variable compression engines allow the volume ...
The APC allowed a higher compression ratio (initially, 8.5:1 as opposed to 7.2:1, and, on 16-valve variants introduced in 1985, 9.0:1). This improved fuel economy and allowed the use of low-octane petrol without causing engine damage caused by knock.
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.
Engine knock or pinging occurs when some of the unburnt gases ahead of the flame in an SI engine spontaneously ignite. This gas is compressed as the flame propagates and the pressure in the combustion chamber rises. The high pressure and corresponding high temperature of unburnt reactants can cause them to spontaneously ignite.
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.
LSPI events are random and infrequent, and their effects on impacted vehicles can include very high-pressure spikes, loud knocking noises and sometimes catastrophic engine damage. [4] It's commonly known as "Detonation or Knock". Engine management systems can overcome pre ignition by the means of a knock or detonation sensor.
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