Craig,

 

There is “another whole issue”  with diesel engines .

 

One that NOBODY has discussed in public.  It is so “silent” that it almost appears that to bring up the subject may be  like breaking wind in church.

 

So… here goes - - you heard it here - - first.

 

The diesel exhaust is cooler.   Is THAT a problem?   No.  But lets think a little further.

 

Why?  

 

Because the CR is much higher.  So the exhaust expansion is more.   OK….

 

But if the CR is much higher then - - so is the peak internal cylinder pressure.

 

OK… but that means that the bulk internal combustion gas temperatures are a lot higher.

 

And that means that you get a LOT more BTU’s transferred into the cylinder head.

 

And, as everybody with some diesel experience is aware - - they tend - - as a result to use rather large radiators.

 

Because that heat  has to be dissipated - - - some way.

 

HOW ?   Either through air cooling through cylinder fins or through a radiator.

 

EITHER WAY  - - -  you end up with an ENGINE that may have a BSFC of around 0.36 to 0.37  (compared to 0.38 to 0.39 for a same horsepower spark ignition engine ) .

 

However - - whatever fuel efficiency is realized - - - is most likely MORE THAN OFFSET  by the additional cooling  drag requirements.

 

End result - - - it likely takes more pounds of fuel to get you from  A to B - - or more Hp to get you the same air speed.

 

Regards,  George

 

 

 

 

 

Bryan J. Burr wrote:

This would be a great engine installation for the ES and Legacy if it fits under the cowling.  Does anyone know if Thielert will sell to the open market (non O.E.M.) and what the pricing would be? 

As per the Theirlert Web Site:

“The Centurion 4.0 was certified by the EASA for the installation in the Cirrus SR 22 on February 12, 2007 already. The certification of the 4.0 for the Cessna 206 is expected in the next days. These two certifications will open the market for deliveries of the 4.0 engine.” 

 

Bryan, I can't find any reference to BSFC on the Thielert web site.  My experience with diesel engines was they are not significantly better than .38 BSFC and they are always heavier than a comparable gas engine for a given power output.  Now there have been some significant diesel engine improvements in the last few years.  A friend of mine has been working intake ports on a diesel engine and he has flow rates very high with valve lifts near one inch.  When you go to direct injection and no pre-chamber, the C/R can go down and these big valve lifts are possible.  Add a couple of big turbos and maybe you have something.  My intuition is, the main advantage is that it can burn Jet A fuel.  If the airliners get their way, gas engines will pay the FAA bill.

Craig Berland