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FOUR-STROKE ENGINE OVERVIEW
(SPARKPLUG .VS. GLOW PLUG)
Are glow plugs in a diesel engine for the same purpose as the sparkplugs
in a gasoline engine?
The short answer is no. The reason I give the short answer is
that I have observed persons read similar articles to this one and come away with an affirmative answer.
GASOLINE ENGINE (sparkplug)
In a four-stroke gasoline engine the fuel and air is mixed somewhere before
the intake valves. This mixture is pulled into the engine cylinder when the intake valves open and the piston starts down away from the
cylinder head for the intake-stroke. At the bottom of the intake-stroke, the intake valves close and the piston travels back towards the
head, compressing the air fuel mixture (compression-stroke). At an appropriate point near the top of the piston travel (Top Dead Center –
TDC of the compression-stroke), a high voltage pulse is applied to the center electrode of the sparkplug causing a spark to jump the gap to the outer
electrode. This spark ignites the air fuel mixture, releasing the chemical energy of the fuel as heat and a large volume of gas, driving
the piston back away from the cylinder head for the power-stroke. At the end of the power-stroke the exhaust valves open and the piston
travels back towards the head expelling the combustion gases for the exhaust-stroke. At the end of the exhaust-stroke, the exhaust valves
close and the process starts all over. In a gasoline engine, the sparkplug ignites the air fuel mixture at the beginning of every power
stroke (similarly in a two-stroke gasoline engine).
DIESEL ENGINE (glow plug)
In a four-stroke diesel engine, the air enters the piston
through the intake valves devoid of fuel. As the piston moves away from the . . .