Bsfc

[Redbone]

Has anyone ever seen BSFC numbers for our Dmax's, stock or hotrodded? I was looking at some numbers from our sprint car and midget alcohol motors and noticed I've never scene them for the GM diesels (or any others for that matter).

On the alky motors, a typical 4 cylinder inline 166 CID producing 350 FWHP with a BSFC of +/-1.0 consumes fuel at rate which could theoretically produce 1200 HP. A typical 410 SBC making 850 FWHP with a 1.0 BSFC could theoretically produce 2900 HP.

It's pretty amazing to realize how inefficient the IC engine really is.

 

[DuramaxPowered]

I don't know the formula to figure BSFC, but my LMM stock says 108^MM3 fuel rate for 365HP.......IIRC LB7 is 98^MM3 for 300HP..Any help?

 

[Redbone]

The BSFC (Brake Specific Fuel Consumption) is the mass of fuel required to produce one horsepower for one hour, or, Lbs./HpHr. Usually get this number from the flowmeter on the engine dyno. Might be interesting to try to back into it by using the tables. I'll see what I come up with.

 

[Redbone]

Here's what I came up with:

Assumptions:
360 HP @ 3200 RPM
30% drivetrain loss
108 mm3 per injection cycle
diesel fuel density = 7.09 lbs/gal
diesel fuel energy = 19,563 BTU/lb

I come up with a BSFC of 0.33 at peak HP. Should be even better at peak TQ.

This would equal a thermal efficiecy of 47.7%, compared to about 29% for the alky motors.

For comparison, a well tuned NA gasser might show low to mid 0.40's.

Anyone know if these numbers sound reasonable?

 

[sweetdiesel]

Is the duty cycle for the injectors 0.89? (LB7)

I came up with 16 lb/hr????????? That cant be right?

 

[sweetdiesel]

Red bone what formula are you using?

 

[Redbone]

Red bone what formula are you using?

S.W.A.G.

Here's how I backed into this, might be totally off the wall.

From DuramaxPowereds post above, at peak horsepower (360HP @ 3200RPM) stock LMM tuning calls for 108mm3. Here I assumed the injector actually delivers 108mm3 of fuel per injection event. This means 1600 injection events per minute, or 172,800 mm3 of fuel per cyliner, per minute.

Carrying this out further for eight cylinders, this means 82,944,000 mm3 per hour, or 21.9 gal/hr. At 7.09 lbs/gal, that's 155.27 lbs/hr.

At 360 RWHP, I assumed 30% drivetrain loss, so I got 514 FWHP. Dividing the fuel mass rate, 155.27 lbs/hr by 514 HP, that's 0.30 lbs/HpHr = BSFC.

For thermal efficiency, consuming 155.27 lbs/hr at 19,563 BTU/lb, that's 3,037,547 BTU/hr. 1 HP = 2545 BTU/hr, so we consumed a potential 1193 HP worth of fuel. Finally 514/1193 = 43%. (ignore the rounding errors from my earlier post).

 

[sweetdiesel]

Thanks Redbone