Quote:
Originally Posted by COLVERT
In a minute or two from start up the engine is beginning to produce enough heat to cause the petrol molecules to break down into millions of smaller molecules. In this form the spark no longer has any trouble igniting them. The choke is no longer necessary and is switched off. This is done manually or slowly by a heat sensor in the water jacket.
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Or a manual choke (that us poor folk had to use), it was a revelation though, with the bimetallic strip on the side of the carb (none of these fancy water jacket sensors - although it had one, but all it did was to cause illumination of a dash light, if the coolant overheated
). Manual choke taught me a little about the 'over-enrichment' of fuel delivery, which I understood to be, that there was too much petrol (it is important at this stage to call the fuel being described) being introduced for the amount of air, so therefore could not be atomised enough to explode, micro, macro and bluddy great droplets (relatively speaking of course). Effectively drowning the explosive force of combustion, and making the exhaust gas smell of petrol.
I know enough about the combustion process that I want to know about, especially nowadays with ecus controlling the mixture. My initial question was about the glow plug. The descriptions above from both you and Mike, (which I do appreciate, please do not get me wrong), would be better served for describing the benefits of bypassing the EGR?
I had never heard of, and did not think it happened, that diesel was sprayed directly onto a glow plug. As a practice I thought it would be both inefficient and destructive to the glow plug. I always thought a glow plug tip would be just in the ignition chamber, being hot, doing its thing, so when compression happened in cold conditions, the extra heat provided gave a more effective (read complete) burn, and therefore, a larger expansion of exhaust gases, ie more power.
With a working injector, it should be relatively fine. With a clogged injector, tiny droplets (not the micro/macro mist) of diesel would be sprayed/fall onto the glow plug tip. This would burn, and ignite any diesel vapour, creating combustion, effectively causing pre ignition (and therefore less power). BUT this is where I wondering. The fuel droplets from a clogged or inefficient injector, would land on and burn at the same point millions of times, as the glow plug doesnt move. This would surely leave a nanoscopic (
) residue. Over time, this residue, would also burn off millions of times. At that physical point, where the residue burns, would be hotter than the surrounding area of the glow plug tip. This would be a weak point, and would cause a failure of the glow plug tip casing, due to the tiny differences in heat expansion of the tip, leading to a failure of the glow plug.