Horse Power and its Effectiveness

[Mike Rolica]

	-Original Message-----
	From:	bearbvd at cmn.net [SMTP:bearbvd at cmn.net]
	Sent:	Tuesday, December 14, 1999 9:50 AM
	To:	gmecm at efi332.eng.ohio-state.edu
	Subject:	RE: Horse Power and its Effectiveness

		>Mike Rolica
		>Meridian Magnesium Products
		>Strathroy, Ont
		>Ext. 260
		>
		>
		>	-----Original Message-----
		>	From:	bearbvd at cmn.net <mailto:bearbvd at cmn.net>
[SMTP:bearbvd at cmn.net] <mailto:[SMTP:bearbvd at cmn.net]> 
		>	Sent:	Monday, December 13, 1999 10:56 PM
		>	To:	gmecm at efi332.eng.ohio-state.edu
<mailto: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!

	Yes, that is true for those minimal amounts of hydrocarbons in the
fuels, but octane and cetane make up a very small amount of the mixture we
call gasoline and diesel fuel.  I've worked in the chemical value in sarnia
for a couple years.... One of the biggest refining centers in north america.
Heating value per pound of diesel is greater.. not cetane, but diesel.
Cetane only accounts for 35% of diesel (no2) And if you want to get real
friggin technical more energy is changed into heat with gasoline than
diesel because of it's slower burn.  If there is too much cyl press, heat is
generated istead of expanding gasses.  
	NO-a large part of it is more horsepower per unit of engine WEIGHT.
Well you might as well put your foot in your mouth now, because yes hp is
why they use gas in airplane engines.... Hp is related to torque.... I said
diesel will produce more torque than a gas but not at high rpm ergo not
allot of hp.  Now if you want to throw some more oranges into the apple
basket A detroit diesel of otherwise known as a 2 stroke produces both lots
of torque and wads of hp.  Airplanes need hp or lots of torque at high rpm
(same thing) as the engine to prop ratio is USUALLY 1:1.  By the time you
geared up a diesel motor to turn a prop, you would have half the torque as a
gas.

	Yes diesel engines become less efficient at high rpm due to slow
burn of diesel and timing required.  But with todays DI tech, I think you
will see that change.


	If what you say is true.. why are all big trucks, trains, busses
diesel?????? And not gas???

		>
		>
		>	Greg
		>