Mike:

Good data. The Turbo-normalized 550 like I have in my Bo has a BSFC of about .38. That's not as far from the diesel efficiency as the TSIO engines. If it had PRISM, it would come in at about .37--doggone close to the diesel without all of the extra fuel weight (and it doesn't stink like diesel fuel!).

It's helpful to compare the best with the best rather than the best with the worst when talking gas vs. diesel.

Walter


On Sep 13, 2005, at 8:35 PM, Mike Hutchins wrote:


Hi Gang,
 
With the recent discussion about the Innodyne turbine and diesel aircraft engines in general there has been some misinformation about the inherent advantage of Jet A over 100LL with regards to energy content. Here is an excellent link to a Chevron web site that covers everything you might want to know about various aviation fuels. In particular, the energy density of jet fuel, on a BTU/Gal basis does show about an 11.8% advantage over Avgas. On the other hand, if you look at the energy density on a BTU/Lb basis, Avgas has the advantage by about 1%.
 
So where does the supposed 30% energy advantage of diesel engines over Avgas engines come from? Do diesel engines really enjoy a 30% efficiency advantage over aircraft engines? In terms of BSFC, they are starting from a 1% disadvantage solely on the basis of the energy content per pound of fuel. Granted, diesel engines operate at a much higher compression ratio (the Thielert Centurion 4.0L engine is 18.5:1) than our Avgas engines, but is that difference sufficient to extract more than 30% efficiency. I don’t think so.
 
Thielert claims a 0.36 BSFC for their 1.7L turbocharged diesel engine with a compression ratio of 18:1. The GAMI folks report that our turbocharged Avgas engines typically achieve a BSFC in the range of 0.41-0.43 when operated LOP. This works out to a 16% efficiency advantage per pound of fuel for the turbo-diesel engine.
 
Taking it a step further, when we fuel up our diesel powered airplane, our fuel tanks will hold the same number of gallons of fuel whether it is Jet A or 100LL, but the Jet A will weigh 17% more than a load of 100LL. Ahh, this is how we get the 30% advantage over our 10LL engines. When we combine the 16% greater load of BTUs per wing with the 16% better efficiency of a turbo-diesel engine, we do, in fact end up with an aircraft that has a 30% greater potential energy conversion than our current rides. Now the question is, can we really go 30% farther between fill ups?
 
Wow, that 350HP, 4.0L certificated (in Europe) turbo-diesel engine is starting to sound pretty good. Too bad it weighs 600 pounds, although Thielert claims the installed weight is comparable to a TCM engine. Time will tell…
 
 
Best Regards,
Mike
 
 
 
 
http://www.chevron.com/products/prodserv/fuels/bulletin/aviationfuel/2_at_fuel_perf.shtm
 
http://www.centurion-engines.com/c40/c40_data.htm