Small diesel engine turning supercharger

[drmiller100]

Originally Posted by ConnClark

Fortunately on a diesel the laws of Thermodynamics don't limit us too much. Adding 10 psi of boost with a roots blower can still improve fuel economy.
http://aerade.cranfield.ac.uk/ara/1936/naca-tn-569.pdf

Edit more proof (page 18 in the pdf)
http://naca.central.cranfield.ac.uk/...report-577.pdf

wrong.

is the goal more power, or more "effiicent"????

those are precombustion chamber engines, and run with incredibly inefficient parameters.

[hawk2100n]

Originally Posted by ConnClark

Fortunately on a diesel the laws of Thermodynamics don't limit us too much. Adding 10 psi of boost with a roots blower can still improve fuel economy.
http://aerade.cranfield.ac.uk/ara/1936/naca-tn-569.pdf

Edit more proof (page 18 in the pdf)
http://naca.central.cranfield.ac.uk/...report-577.pdf

The OM 617 in your 300SD is one of the last common engines with precombustion chambers. I had a 300TD. But the best way to drive these cars for max fuel economy is below the onset of boost when possible, which is hard. Same goes for all diesel engines. Turbos are for power. I usually got around 27 mpg in my wagon. It's still in the family. My dad is hanging on to it but he and I bought it together when I was in high school. 230,000 miles on it now.

[mechman600]

Originally Posted by drmiller100

those are precombustion chamber engines, and run with incredibly inefficient parameters.

Exactly. That was the best technology they had, when super fine spray patterns and high injection pressures were not yet possible because of lack of machining tolerances and "pre-cups" were the only way to make it work. Injection pressure was probably peaking at 4000 psi at rated HP, where even an older TDI (rotary pump) will hit 15000.

Originally Posted by hawk2100n

But the best way to drive these cars for max fuel economy is below the onset of boost when possible, which is hard.

This is because when boost isn't there, the air/fuel control in the fuel pump limits rack travel, AKA fuel quantity per stroke. Electronic engines do a variation of the same by limiting mm3 per stroke until boost reaches a certain level (smoke limiting) and EGR flow reaches a certain level (NOx limiting).

[ConnClark]

More boost raises engine efficiency. Had to find it in the internet archive but here it is and it says the same thing as the earlier papers (From 2004 on a Direct Injection engine).
http://web.archive.org/web/200611080...4/A6_1_022.pdf

As far as efficiently driving a turbo diesel engine you want to drive generating low boost pressures. That shows the pistons are extracting as much power as they can before they dump the rest of the energy in the combustion gases to the turbine.

As far as the engine itself you want it to generate the most boost as efficiently as possible. The purpose of the waste gate is to keep boost pressures in a range to avoid wear and tear on the engine and keep the boost in an efficient range of the compressor map and keep back pressure in check.

So, if you are trying to increase the boost setting on your current system you probably won't improve efficiency. If you improve it by using a more efficient turbo you can raise boost and get better fuel economy