Why does a diesel engine do not require spark plug to start?

Question

All petrol engines require spark plug to start which provides a spark to ignite the air-petrol mixture,but how does a mixture of diesel-air ignite resulting combustion in diesel engine without spark plug?

Answer 1

the engine produces 500 pounds compression wich gets hot on its own at or neer top dead center the fuel is sprayed in and the heat ignites it as it is sprayed in
on a cold engine there may not be enoulf heat so they give it a little extra

if all the glow plugs fail it will still start if the engine spins fast enoulf

Answer 2

When compressed beyond a certain point, an air-fuel mixture becomes so unstable (due to heat and closeness of the molecules) that it ignites without spark. The energy produced from the compression and the subsequent collisions of atoms takes the place of the energy of the spark. This is the case with diesels. In order to prevent combustion before the piston is in position, the fuel is not injected into the cylinder until just the precise moment. When the piston is in position the fuel is injected in an instant and, as it does so, combustion occurs. The timing of the injection of fuel performs the same function as the timing of the spark in a conventional engine.

Answer 3

Diesels have like 25 [or more] to 1 compression ratio, compaired to a gas motor that has maybe 8 to 1[ give or take a few] . The compression is so high is why ignites . BUTT some Diesels have to have GLOW plugs to get them started - butt they are a constant heat source , unlike a spark plug & the GLOW plugs are controled by a relay or if need be they can be hooked up to a toggle switch which has been done on older equipment OR if U don't want 2 buy a relay (not reccommened)

Answer 4

Because diesel is a fuel oil and becomes volatile under pressure. The piston compresses the air in the cylinder and that supper heats the air. The diesel is injected and the heat of compression ignites the fuel oil and air mixture.
FYI - Glow plugs are use before the first start of the day or after long periods of non use (as in the engine has cooled down) to pre heat the air in the cylinder before starting.

Answer 5

High compression = high heat = combustion. Because diesel has a lower volatility, when it ignites it burns slower and gives most of it's power on the downward stroke. That's why even cooking oil can be used for fuel. When you compress air to say half the volume it normally is, the temperature in that air doubles. At room temp. of say 80 degrees when it is squeezed to 1/4 it's former size, the temp. is now 320 degrees. And so on. High pressure heats the air, add Fuel and you have combustion Add fuel that burns slow, and you have diesel power.

Answer 6

Diesel engines work by compressing the fuel/air mix. As the compression increases, the mix heats-up until it's hot enough to ignite the mix, giving you the power. But, this method is a bit unpredictable. The exact timing of when the mix will finaly go BANG varies a tiny bit, as the air & fuel components vary. Because of this variance, a diesel engine is a bit slower to make rpms, & it doesn't go as 'fast' as a gas engine. Plus, because the compression ratio of a diesel is much higher then a gas engine, the diesel is heavier. To compare to a gas engine, just basically the opposite.

Answer 7

The compression in a diesel engine is much higher than a petrol engine,and it is this force of pressure that causes the mixture--diesel and air to explode.To withstand this extra compression the diesel engine is made of stronger construction and thus is much heavier

Answer 8

A gas under pressure heats up. Physics 101. Therefore is hot enough to ignite the fuel by compression. Or also known as Spontaneous Combustion.

Answer 9

When the piston goes up it compresses the diesel-air mixture to that point at which that much amount of heat can be generated at which diesel ignites.

Answer 10

just to add another point:
some really old diesel engines don't even have glow plugs but a manifold heater which is a bit like a cigarette lighter in the side of the inlet manifold but when it heats up to glow red hot, the heat opens a valve from a small diesel reservoir which then pours diesel past the hot bit and burning diesel goes down the inlet manifold. i had that in my bedford cf campervan with a perkins 154 engine