8/6/2019 Dieseling
1/2
Dieseling or engine run-on is a condition which can occur
inspark plug,gasolinepoweredinternalcombustion engineswhereby the
engine keeps running for a short period after being turned off,
dueto fuel igniting without a spark.
Dieseling is so-named because it is similar in appearance to
howdiesel engines operate - by firingwithout a spark. The ignition
source in a diesel is the compression of the fuel in the cylinder
rather
than a spark as in gasoline engines. The dieseling phenomenon
occurs not because the compressionratio is sufficient enough to
cause auto-ignition of the fuel, but a hot spot inside the cylinder
startscombustion. An automobile engine that is dieseling will
typically sputter then gradually stop.
Dieseling is not nearly as common as it once was because it most
commonly occurs in carburettedengines. The vast majority of
American, European, and Japanese vehicles manufactured after
1990are fuel-injectedthe injectors and high-pressure fuel pump
immediately cease supplying fuel to thecylinders when the ignition
is switched off. If the injector is damaged or malfunctioning, a
smallamount of fuel can enter the chamber and be ignited, causing a
sputter or two after the engine isswitched off.
Dieseling (in the sense of engine run-on, and disregarding
combustible gaseous mixtures via the airintake) does also occur in
diesel engines, when the piston or sealing fails due to
overheating, andadmits engine oil into the cylinder. A structurally
failing diesel engine will often accelerate when
throttle is released, and even after fuel injection is switched
off.
Some carburetted engines have fuel pumps, but they are often
low-pressure. They are typicallydesigned only to overcome a loss of
suction in the fuel line near the engine due to fuel evaporation
inhot weather, to supply sufficient fuel to
maintainstoichiometriccombustion under heavy load withwide-open
throttle, or a combination of the two. Fuel demand is low at idle
and there is more thanenough manifold vacuum to draw sufficient
fuel for combustion even if the fuel pump is switched off.
Gasoline engines that are much smaller than the typical
automotive engine are usually carburettedfor economic and
engineering reasons. Dieseling can occur in such engines. These
engines includethose installed in mopeds, scooters, small
motorcycles, ATVs, and most lawn-and-garden power tools.
Contents [hide]
1 Potential causes
2 Potential fixes
3 References
4 External links
Potential causes
This condition can occur for a multitude of reasons:
Built-up carbonin the ignition chamber can glow red after the
engine is off, providing amechanism for sparking unburnt fuel. Such
a thing can happen when the engine runs veryrich, depositing
unspent fuel and particles on the pistons and valves. Similarly,
non-smoothmetal regions within the pistonchamber can cause this
same problem, since they can glowred. It has also been suggested
that an improperly rated spark plug can retain heat and causethe
same problem.
A carburetor that does not close entirely can contribute to
running once the engine is off,since the extra fuel and
oxygenmixture can combust easily in the warm piston
chamber.Similarly, hot vaporizedoil gases from the engine crankcase
can provide ample fuel fordieseling.
Incorrect timing.
http://www.answers.com/topic/spark-plughttp://www.answers.com/topic/spark-plughttp://www.answers.com/topic/gasolinehttp://www.answers.com/topic/gasolinehttp://www.answers.com/topic/gasolinehttp://www.answers.com/topic/internal-combustion-enginehttp://www.answers.com/topic/internal-combustion-enginehttp://www.answers.com/topic/internal-combustion-enginehttp://www.answers.com/topic/internal-combustion-enginehttp://www.answers.com/topic/fuelhttp://www.answers.com/topic/diesel-enginehttp://www.answers.com/topic/diesel-enginehttp://www.answers.com/topic/automobilehttp://www.answers.com/topic/stoichiometryhttp://www.answers.com/topic/stoichiometryhttp://www.answers.com/topic/stoichiometryhttp://toggletoc%28%29/http://toggletoc%28%29/http://www.answers.com/topic/dieseling#Potential_causeshttp://www.answers.com/topic/dieseling#Potential_fixeshttp://www.answers.com/topic/dieseling#Referenceshttp://www.answers.com/topic/dieseling#External_linkshttp://www.answers.com/topic/carbonhttp://www.answers.com/topic/carbonhttp://www.answers.com/topic/poppet-valvehttp://www.answers.com/topic/pistonhttp://www.answers.com/topic/pistonhttp://www.answers.com/topic/carburetorhttp://www.answers.com/topic/fuelhttp://www.answers.com/topic/oxygenhttp://www.answers.com/topic/oxygenhttp://www.answers.com/topic/evaporationhttp://www.answers.com/topic/evaporationhttp://www.answers.com/topic/crankcase-2http://www.answers.com/topic/spark-plughttp://www.answers.com/topic/gasolinehttp://www.answers.com/topic/internal-combustion-enginehttp://www.answers.com/topic/internal-combustion-enginehttp://www.answers.com/topic/fuelhttp://www.answers.com/topic/diesel-enginehttp://www.answers.com/topic/automobilehttp://www.answers.com/topic/stoichiometryhttp://toggletoc%28%29/http://www.answers.com/topic/dieseling#Potential_causeshttp://www.answers.com/topic/dieseling#Potential_fixeshttp://www.answers.com/topic/dieseling#Referenceshttp://www.answers.com/topic/dieseling#External_linkshttp://www.answers.com/topic/carbonhttp://www.answers.com/topic/poppet-valvehttp://www.answers.com/topic/pistonhttp://www.answers.com/topic/carburetorhttp://www.answers.com/topic/fuelhttp://www.answers.com/topic/oxygenhttp://www.answers.com/topic/evaporationhttp://www.answers.com/topic/crankcase-2
8/6/2019 Dieseling
2/2
An engine that runs too hot or too lean may produce an
environment conducive to allowingunspent fuel to combust.
An idle speedthat is too fast can leave the engine with too much
angular momentum uponshutdown, raising the chances that the engine
can turnover and combust more fuel and lockitself into a cycle of
continuous running.
Potential fixes
Items similar to carburetor cleaners and carbon cleaners have
been suggested as partial remedies forattempting to clean the
piston chambers and valves of engines that run too rich.
For those engines that have sharp metallic edges, it has been
noted that poorly milled heads andblocks can contribute to this
problem, so having the rough spots smoothed may help.
For those engines that run too hot or too lean, verify that all
mechanisms in place to cool the engineproperly function as they
should. Replace the thermostat if necessary. Clean the radiator.
Verify thatall auxiliary fans engage at their proper temperatures,
and ensure that the thermostatic sensors on
belt driven fans engage as necessary.
In the case that there is too much angular momentum, lower the
idle speed if possible.
Read
more:http://www.answers.com/topic/dieseling#ixzz1T8f3CvOS
http://www.answers.com/topic/idle-speedhttp://www.answers.com/topic/idle-speedhttp://www.answers.com/topic/angular-momentumhttp://www.answers.com/topic/thermostathttp://www.answers.com/topic/radiatorhttp://www.answers.com/topic/dieseling#ixzz1T8f3CvOShttp://www.answers.com/topic/dieseling#ixzz1T8f3CvOShttp://www.answers.com/topic/idle-speedhttp://www.answers.com/topic/angular-momentumhttp://www.answers.com/topic/thermostathttp://www.answers.com/topic/radiatorhttp://www.answers.com/topic/dieseling#ixzz1T8f3CvOS
