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In spark-ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.
To detect knock, a piezoelectric knock sensor (basically a microphone) bolted to the engine block responds to unique frequencies caused by engine knock. The sensor generates a small voltage that is sent to the electronic control unit , which processes the signal to determine if, in fact, knock is occurring.
Dieseling (in the sense of engine run-on, and disregarding combustible gaseous mixtures via the air intake) can also occur in diesel engines, when the piston or seals fail due to overheating, admitting engine oil into the cylinder. A structurally failing diesel engine will often accelerate when the throttle is released, even after fuel ...
The result is an engine that fails to maintain idle RPM and frequently stalls. A jammed actuator may be freed simply by cleaning it. However an actuator that has stopped working due to a fault in its servomotor will need replacement. Air leaks in either the stepper housing or pipes will cause elevated idle RPM.
Modern direct injection diesel engines combine stratified charge (SC) with compression ignition (CI), abbreviated as SCCI. As in HCSI, HCCI injects fuel during the intake stroke. However, rather than using an electric discharge (spark) to ignite a portion of the mixture, HCCI raises density and temperature by compression until the entire ...
1952 Shell Oil film showing the development of the diesel engine from 1877. The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is called a compression-ignition engine (CI engine).
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Scavenging is the process of replacing the exhaust gas in a cylinder of an internal combustion engine with the fresh air–fuel mixture (or fresh air, in the case of direct-injection engines) for the next cycle. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power ...