Horse Power and its Effectiveness

[Greg Hermann]

>Mike Rolica
>Meridian Magnesium Products
>Strathroy, Ont
>Ext. 260
>
>
>	-----Original Message-----
>	From:	bearbvd at cmn.net [SMTP:bearbvd at cmn.net]
>	Sent:	Monday, December 13, 1999 10:56 PM
>	To:	gmecm at efi332.eng.ohio-state.edu
>	Subject:	Re: Horse Power and its Effectiveness
>
>	>At 09:16 PM 12/13/1999 -0500, you wrote:
>	>>A few comments:
>	>>
>	>>For a given displacement, long stroke means small bore means less
>force.
>	>>This exactly balances out the longer moment arm.  Long stroke
>motors have a
>	>>harder time at high revs (due to both inertia and limited
>breathing) but
>	>>they offer no advantage in low speed torque.
>	>>
>	>>Diesel engines make less torque than gas engines (naturally
>aspirated).
>	>>Their advantage is the BMEP is not limited by detonation so they
>can take
>	>>gobs of boost.
>	>
>	>Since when do they make less torque?
>
>	Since forever. Because a diesel cycle at full throttle is not as
>efficient
>	as an Otto cycle at full throttle for equal compression ratios.
>
>	>The cummins 5.4L I6 makes 650 lb/ft in full trim at 1800 RPM.
>Tuned down
>	>for Dodge, It makes 400 Lb/ft at 1800 RPM...  Would love to see a
>gas I6
>	>5.4L engine do that!
>
>	Would love to see the Cummins 6BT do that without the "T"!! Gary DID
>say
>	"NA", I think!
>
>	Guess why there are NO piston engined aircraft that use the diesel
>cycle??  Because they do not rev high enough.  Don't make the high rpm
>torque that an airplane neads...!  IT IS SIMPLE  1 GALLON OF DIESEL HAS
>ABOUT 2/3RD MORE BTU'S THAN A GALLON OF GAS!  More energy before = more
>energy converted to mech!  K.I.S.S.

NO--a large part of it is more horsepower per unit of engine WEIGHT. The
lower heating value (per pound) of diesel fuel is actually somewhat LOWER
than the lower heating value of gasoline. (hexadecane (cetane) = 18,898
BTU/lb., 6.45 #/gallon; isooctane = 19,065 BTU/lb., 5.77 #/gallon , Yes,
the diesel is somewhat more dense, but barely more than enough to make up
the difference in heating value--BUT--heating value per POUND is far more
significant for an aircraft than heating value per GALLON!

Greg
>
>
>	Greg
>