I was intrigued to learn that Mercedes has been using direct-injection diesels in its trucks, buses etc (and of course the Unimogs) in Europe for years, well before the high-pressure, common rail, electronically controlled engines were developed.

At the same time, all the Mercedes diesel car engines used an indirect-injection design with a precombustion chamber until the CDI came out.

Otherwise, the engines seem fairly comparable in horsepower and used mechanical injection pumps. From what I understand, the prechamber design was used to decrease exhaust smoke (more efficient combustion) and noise levels. So my guess is, the direct-injection design would be too loud & smoky to be used on a fine Mercedes motorcar, until/unless the technology could be improved. Is this correct?

I'm just curious as to why Mercedes didn't use these engines on any diesel car, as the OM3xx engines seem like they have an even simpler, more reliable design than an OM616/617/603, and possibly are slightly more powerful for their size.

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1976 240D "Katja"

#1 noise. DI engines are much noisier, go listen to a Cummins b-series and compare it to your Mercedes. The other consideration is of course emissions. I don't know how they compare exactly, but I wouldn't say that the prechamber is more efficient per say. Afterall, as you pointed out, DI engines typically offer more power for the same displacement, and don't suffer the pumping losses associated with a prechamber. So I really think because of noise and drivability (wider rpm range with IDI).

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For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel

That about sums it up.

Direct Injection is more efficient I believe....but there's the noise issue and the low rpms aren't as pleasant in a car...for most people. I'd love a truckish diesel.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
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'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

IDI is about 15% less efficient because of heat loss to larger surface area and pumping losses moving air through a restricted air passage.

The 2.9L OM602.98x is direct injection and the father of CDI. Obviously it was only used outside the USA.

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