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IDI combustion theory ?
I would like to know, Does the prechamber cup itself get hot enough once running to help support combustion? Or does the glow plug stay hot enough once a few combustion cycles are achieved.
I used to fly glow plug engined model airplanes. Once in while they would stop unexpectedly and sure enough the glow plug wire loop was not in the present in the glow plug. I know that the glow plug engines were not strictly diesels but they seemed to have some similarities in that they they were not spark ignition. Their fuels were perhaps more active with methanol and nitromethane. I could see why they were two strokes to keep things simple lightweight and keep the glow plug hot.
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85 Merc 300D - Unwinding 31 years of wear 86 VW TD Mahindra Diesel Iseki Diesel In 2007 I didn't own a diesel. |
#2
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The fuel is vaporized in the prechamber when the motor is running. The compression then causes the heat necessary to cause combustion. When running the compression achieved is much greater than when doing a compression test. The glow plug motor comparison is without merit. You can get 2 stroke diesel model airplane motors. They are purely compression ignition.
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Grumpy Old Diesel Owners Club group I no longer question authority, I annoy authority. More effect, less effort.... 1967 230-6 auto parts car. rust bucket. 1980 300D now parts car 800k miles 1984 300D 500k miles 1987 250td 160k miles English import 2001 jeep turbo diesel 130k miles 1998 jeep tdi ~ followed me home. Needs a turbo. 1968 Ford F750 truck. 6-354 diesel conversion. Other toys ~J.D.,Cat & GM ~ mainly earth moving |
#3
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I actually believe the location of the Ball Pin allows worn Injectors to still be functional once the Ball Pin heats up. The other popular type of IDI precombustion Chamber is the Squish Chamber (Old VW Rabbit Engines). I focuses part of the Injector Spray against part of the Chamber Wall to do the same thing. However the Chamber Wall is against the Cylinder Head and it must remain a lot cooler than the Ball Pin does. Anything that retains heat in the Precombustion Chamber must help with Comboustion. However, if the Injector spray gets too close to the Glow PLug it will burn through it.
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84 300D, 82 Volvo 244Gl Diesel Last edited by Diesel911; 01-19-2013 at 06:54 PM. |
#4
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I have an 86 Jetta TD which is probably just as you describe. I get 55 mpg (US) with it.
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85 Merc 300D - Unwinding 31 years of wear 86 VW TD Mahindra Diesel Iseki Diesel In 2007 I didn't own a diesel. |
#5
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When I rebuilt the block I used oversized Pistons for a VW Rabbit that were made in Brazil.
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84 300D, 82 Volvo 244Gl Diesel |
#6
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Think of the glow plugs as performing the task of a block heater - but instead of heating the water jacket around the cylinders they warm up the air in the combustion chamber.
As mentioned above by layback40 heat is produced during the compression stroke. (Quickly) Compress air and it gets hot. (Quickly) expand air and it gets cold => don't hold onto a nozzle of a CO2 fire extinguisher and release the gas! Even though quickly compressed air gets hot; unfortunately on a cold engine this heat buggers off quite quickly into the surrounding parts of the engine. The glow plugs give a bit of a boost. They are only in use before the engine starts - they are not used like a spark plug (or the model aircraft example you gave) to ignite the fuel once the engine is running. Here's a nice link telling more Indirect injection - Wikipedia, the free encyclopedia
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1992 W201 190E 1.8 171,000 km - Daily driver 1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone 1965 Land Rover Series 2a Station Wagon CIS recovery therapy! 1961 Volvo PV544 Bare metal rat rod-ish thing I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior Don't leave that there - I'll take it to bits! |
#7
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So the Ball Pin (sort of a bridle) in the pre chamber acts similar to a constantly running glow plug. I guess I didn't see them when I had the injectors out.
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85 Merc 300D - Unwinding 31 years of wear 86 VW TD Mahindra Diesel Iseki Diesel In 2007 I didn't own a diesel. |
#8
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I don't believe the diffuser ball glows, as they're always black when you remove the injectors. Their purpose is to help atomize the fuel spray and reduce ignition delay. The reason Mercedes has such a complicated combustion system is to make the engine quiet enough for a luxury car.
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'83 300D, 126K miles. |
#9
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84 300D, 82 Volvo 244Gl Diesel |
#10
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Next time you have the injectors out, turn the glow plugs on and you'll be able to see the ball pin. Very cool.
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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked |
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