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how is it that some diesel engines need a heater plug for cold start and some dont?
By Bhooshan 06 June 2009

Hi mate, the diesel is much thicker than petrol, therefore it needs to be heated, but now days we have CRDi technology, which is Common rail diesel ignition pretty much same as MPFI , Multi point fuel injection system, instead of a carburetor there is a direct injection, also used in Tractors from New Holland. So the new model's of diesel don't need a heater plug.

Answer by Aman Chaswal 06 June 2009

The deisel actually does not have to be heated. Deisel, unlike petrol, does not catch fire when exposed to a naked flame. (I may be wrong, pls excuse me if i am)
In the deisel cycle hot air (which in older cars was heated using the glow plug/heater during start up) is injected into the cylinder which causes the deisel to ignite and produce the power cycle.

Answer by Quraish Umrethi 06 June 2009

All Diesels need a heater for cold start to bring down the "flash point" of combustion.You dont see some engines having this as they have a clever way of automating this process.Some begin heating as soon as you open da door based on the engine temp sensing luxury segment cars.

Answer by Wilfrid Fernandes 06 June 2009

Older diesel engines (pre-CRDi) were Indirect Injection Engines or IDI engines. In these engines, the diesel was injected into a pre-combustion chamber, which was located either in the cylinder head or in the piston itself. The fuel pumps used in these cars were rotary pumps that ran off the cam-belt or through gears. These pumps did not develop as high pressures that the present CRDi pumps develop. Therefore, in a cold start, it was necessary to heat up the cylinder (and not the diesel, as someone has suggested earlier) so that when the fuel is injected, it ignites. Once the engine is fired up and after it warms up sufficiently, there was no need for the heater plugs to work.
CDRi engines are Direct Injection or DI engines and the Common Rail Pumps used in these engines are very high pressure pumps. In a DI engine, there is no pre-combustion chamber and the compression ratio is also higher. This, coupled with the high pressure and fine spray injection of the Common Rail pump, ensures ignition instantly, even in a cold start. It is not that there are no heater plugs in these engines, it is just that they work only for a fraction of a second, which one usually doesn't notice.
If you ever see a bus or a truck starting, you will notice that they don't wait for a heater plug, as they are large capacity, high compression DI engines.
Hope this answers the question!

Answer by Sasi Menon 06 June 2009
Expert`s comment:

In diesel engines the heater plug is used for heating the air inside combustion chanber. As the combustion process takes place due to compression ignition, during starting of ignition heating the combustion chamber helps for starting combustion. Its needed for all engines but the time duration varies.

Answer by Shiva Shankar 06 June 2009
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