I would like to know more about the differences in running behaviour between Pre-Chamber and Direct Diesels. Having owned several non-TDI VW's of both types in the past, I know the Pre-Chamber types have more of the "clatter-balls" noise at idle. Also, with VW, their Pre-Chamber engines had less power than the later direct injectors; for the 1.6 litre, it was 48 HP vs 52 I believe. I have noticed my 300D has similar idle clatter- is there a reason for more noise with the pre-chamber engines? And ultimately, which is really better?

Any and all words of wisdom welcome!

Dave

The physics behind this, I do not know. The fuel is not pre-heated in the chamber, but is directly injected. VW claims this is the reason behind less smoke and noise. Once the cylinder is warm I don't understand the need to pre-heat the fuel. Maybe with TDI, it is a more precise measure and time of injection than our oldies.

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1984 300D Turbo Sedan (Hilda) 272,115 miles.....
Anthracite Gray/Palamino Leather, I am 3rd owner

2001 Dodge Stratus (Silver) (wifes) 55814 miles...

1982 280TE Wagon Astral Silver Metallic/
Anthracite Velour
260,512 miles (Eva)

1969 230 Sedan Olive Green/Black MBTex
4 Speed Manual
84,213 miles ????
Haus Frau


2004 Boreem Ninja Pocket Bike
Highly Modified 49cc (Ling Ling)

Einigkeit und Recht und Freiheit

Pre chambers heat as well as create a swirl of extra rich mixture which balances out once it reaches the main chambers, the reason pre-chambers were popular in early days is because DI engines, although more powerful than their IDI counterparts, tended to be noisy and vibration prone, therefore DI engines were mostly used in commercial applications. However with emission laws getting strict, and the race for power becoming an important marketing tool and priority, DI, especially CRDI has made a huge comeback in sanitized form today.

I believe that the direct injection models, particularly the common rail types, use higher pressure than the indirect designs. This higher pressure presumably provides better atomization of the fuel spray and allows the spray to be made directly into the combustion chamber.

On the TDI (I have a Jetta TDI Wagon) there is a solenoid on the injection pump that relieves the pressure once the correct amount of fuel has been delivered, which eliminates the smoke from overfueling when you floor it.

Which is better? Define better Direct injection produces more HP, more torque, with less fuel, lower emissions and a smoother engine - just look at the specs of the latest MB CDI engine. But, it is dependant upon engine management systems to do this. The system needs to know crank position, turbo boost, engine temperature, and throttle position at a minimum, each of which requires a sensor and associated wiring. It won't be long before none of the light car diesels are anything but direct injection.

Early gasoline fuel injection had a single injector spraying into a throttle body, then we had multiple injectors, now gas engines are being produced with direct injection too.

Kevin

For more info on VW TDIs, read this: http://tdiclub.com/TDIFAQ/

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'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate

The new VW TDI's can smoke too at full throttle. I've seen it with my own eyes.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Read

It seems the benefits for IDI engines are

1. more rapid mixing of fuel/air
2. broader power band over progressive engine speed
3. quieter running

Benefits for a DI engine

1. much better fuel economy due to lack of heat loss
2. much more torque available on tap
3. easier to start in colder air temps.

Now, quietness has been achieved through electronic sensors. If those electronics never required replacement, I'd say the new engines are vastly superior to anything designed before the common-rail/TDI.. Kudos to the dual-pilot injection on the E320 CDI, and the extra USA spec diesel sound insulation.

sorry for that previous, unrelated reply (i can't work out how to delete it now).

It was ment to be a reply to another post. Show's what happens when you open too many windows at once!

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Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32

Especially when you add fat-hole injectors and add a tuning box or chip to the mix.

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1987 300D Turbo
2000 VW Golf TDI
2008 E320 Bluetec