Quote:
Originally Posted by MorphDaCivic
Welcome James
I have often wondered why no one has tried to produce a scaled down version of a high performance diesel engine like the Audi R10 TDI. Using only 2 or 3 cylinders and high boost pressure. This would reduce size and weight of the engine. I think high fuel economy could be attained.
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I think the issue is basically getting the air system to work. Turbos don't really scale easily, so for a small capacity engine to run high boost pressures you need an over-sized turbo. This means transient response will be poor. To overcome this you need a twin turbo system, a small one for low speeds, and a big one for high speeds/loads. This is why BMW fit 2 turbos which to the 123d and 535d, and 3 to the 550d! And they're not even small capacity engines.
One interesting tech is the CPT electric supercharger which can be used to fill in the low end torque, allowing a large turbo for high load. Needs more control and calibration effort, but has been demonstrated a few times.