Turbocharging a diesel engine?

[Karl2]

Originally Posted by DennisRB

Guys you need to reed Maximum Boost by Corky Bell. You might be lucky to see 2-4psi in the exhaust pipe after the turbine, not before it. Maybe the same ideas will be more believable from they guy who literally wrote one of best books on turbocharging.



http://www.amazon.com/Maximum-Boost-.../dp/0837601606

Legend has it that this book is also very easy to download in PDF format for free.

Have a copy of Mr. Bell’s book and I agree, well written and a wealth of information. I have enjoyed it immensely.
When I buy and turbo charge my Alfa Romeo 1750 Berlina this book will be my bible (Yet another project that I will go to my grave wishing I had done).
His book about Supercharging is equally well written and informative.

Mr. Bells book deals with gas engines and to a large extent some pretty extreme applications and references (800 hp V8’s, 1.000 hp F1 engines etc. etc.). The principals and theories covered in the book are relevant for turbo charging in general (Gas & Diesel) but there are some fundamental differences (Absence of air volume control (throttle plates) in a diesel, the need to maintain your fuel/air mixture in a narrow stoichiometric band in a gas motor, the need to design yourself out of pre-ignition in a gas motor, the typical diesel cam having less overlap, etc. etc.)

I highlighted in my previous post “…in the context of this post…”.
The original post stated: “….turbocharging of diesel engines. Looking more at large installations for ships and things…”. Given the original post and my assumptions (Dangerous, I know) regarding the author of the posts intent (Moderate power increase ?) I maintain that any relationship between intake and exhaust manifold pressure is irrelevant.

Karl2

[Submarine Tom]

It depends a hell of a lot on how much boost pressure you are using (intake).

-Tom

[Karl2]

Originally Posted by Submarine Tom

It depends a hell of a lot on how much boost pressure you are using (intake).

-Tom

I maintain that in the context of the question from the original post the relationship between exhaust pressure (Before the turbine) and intake manifold pressure (boost pressure) is irrelevant.
And, again, with the original post in mind "Looking more at large installations for ships and things" this would not be an application where you would design and deploy a waste gate turbo system. You would select the appropriate "fixed" turbo and the boost pressure curve would be what it would be.

But for the sake of good discussion and exchange....
This could become an issue if the pressure before the turbine dramatically exceeds the boost pressure. Even at that it would only become an issue during valve overlap. In a production diesel engine this overlap is very short.

In modern production and high performance diesels it is common to run max boost at 30 psi, 40 psi and even higher. Combine this with the short overlap and you will find that you don't have an issue.

Should the boost pressure exceed the pressure before the turbine you have a very good thing and, according to Mr. Bell (and in reference to gasoline engines): "..you can begin to make serious power..."

If the author of the original post were to move forward with his project and find at the end of the day that he has an issue with these pressures it means that he has completely missed the boat with his turbo charger selection. He has selected a turbo completely unsuited for the application - The pressure issue would be only the top of the iceberg, he would be faced with a number of issues related to this turbo selection - At least the turbine section of the selected turbo to small, will probably exceed specified max turbine speed resulting in the turbine coming apart, bearing/shaft failures etc. etc. The compressor side of this turbo would probably be too small too resulting in low boost and dismal power/efficiency gain.

Karl

[copenhagen]

Forget all the articles on turbocharging gas engines... on a diesel you can easilt add a turbo without worrying about compression ratios, but you do have to change the injection timing to keep the EGT down.

In an ideal world you would change the pistons to turbo pistion to lower the compression down into the 18-22:1 range but you can run stock ones without issues at moderate boost levels
the cheap option is to cut valvereliefs in the pistons (you can rent the tool from most engineshops)
If you are running an injectionchamber diesel like a toyota 2L you should get a turbo head.. but the above fix is fine (valve reliefs also allow you to have the cam reground to a more aggressive lobe)

in a car or truck its important to run a turbo specific injection pump as the load isnt closely related to RPM, but in a boat its not as important.

but if you just add a turbo, keep the boost below 10 psi and retard the injection point at load to a point where the egt is arround 850 F you shouldnt see much deteriorated fuelefficiency at low load.. and a 30% powergain at load with less than 30% increase in fuelconsumption (the reason for this is if your torbo is sized right you will have more increase of pressure on the cold side than on the hot, resulting in reduced pumping losses

and yes ive done it myself on a toyota 2L (including the cam change) and the above is a parafrase of what ive learned... (final lesson : 40 psi boost and propane injection will kill a toyota)

PS: sorry for my spelling but im using a new laptop and the keyboard is just not compatible with my fingersize