Archives >> Power Strokes 1999-up (4/99-7/99)

Pages: 1
Gary
Member
Member # 472
Reged: 04/06/99
Posts: 88
Loc: Aledo, Texas, USA
FUEL CONSUMPTION AT IDLE
#181851 - 04/08/99 11:39 AM

I AM INTERESTED IF ANYONE HAS EVER CALCULATED OUR FUEL CONSUMPTION WHEN IDLING. LIKE THE 18 WHEELERS, I SOMETIMES FIND MYSELF NAPPING AT THE TRUCK STOPS WHILE LEAVING THE TRUCK IDLING. EITHER FOR THE AC OR THE HEAT. I KNOW I CAN CALCULATE THIS OVER TIME BUT I AM LOOKING FOR THE QUICK ANSWER.

Anonymous
Unregistered
Re: FUEL CONSUMPTION AT IDLE new
#181852 - 04/08/99 01:46 PM

I don't want to sound like a smart-a-- but at idle not moving, you are getting exactly 0 mile per gallon.
Bill S.

Alan_Hepburn
Member
Member # 47
Reged: 04/01/99
Posts: 854
Loc: San Jose, CA, USA
Re: FUEL CONSUMPTION AT IDLE new
#181853 - 04/08/99 01:57 PM

I'll nitpick here: Gary asked for fuel CONSUMPTION, not fuel MILEAGE! Consumption is usually expressed in terms of gallons per hour - at idle a diesel engine typically runs an air/fuel ratio of about 200:1 so if you know the capacity of the cylinders you should be able to calculate the consumption.

------------------
Alan Hepburn - F450 CC PSD XLT+ 4R100

Doug J
Member
Member # 9
Reged: 04/01/99
Posts: 377
Loc: Vancouver, Washington, U.S.A.
Re: FUEL CONSUMPTION AT IDLE new
#181854 - 04/08/99 02:08 PM

With a capacity of 7.3 liters divided by 8 cylinders = .9125 liters per cylinder X 600 rpm at idle = 547.5 liters X 60 minutes in an hour = 32,850 liters divided by a 200 to 1 ratio = 164.25 liters per hour consumption. WAIT A MINUTE - Something went wrong here! I guess this is why they don't let me do the budget around here.

------------------
Doug J
Washington State
99 F350 4X4 SC LB 6spd



jlloyd
Member
Member # 32
Reged: 04/01/99
Posts: 489
Loc: Beaverton, Oregon
Re: FUEL CONSUMPTION AT IDLE new
#181855 - 04/08/99 03:11 PM

I believe 1-2 quarts / hour is in the ballpark. I've let mine idle at home after hand topping up a tank, come back in ~15 minutes and could still see the fuel in the filler neck.

------------------
John S. Lloyd
97 F250 SC 4x4 E4OD 4.10


Alan_Hepburn
Member
Member # 47
Reged: 04/01/99
Posts: 854
Loc: San Jose, CA, USA
Re: FUEL CONSUMPTION AT IDLE new
#181856 - 04/08/99 04:37 PM

Doug tries to figure out fuel consumption at idle:

"...7.3 liters divided by 8 cylinders = .9125 liters per cylinder X 600 rpm at idle = 547.5 liters X 60 minutes in an hour = 32,850 liters divided by a 200 to 1 ratio = 164.25 liters per hour consumption..."

I've often wondered if it was that simple to figure out how much fuel is used ... I think it's a bit more complex than just looking at the size of the cylinder; is the air/fuel ratio based on the cylinder volume at the bottom of the stroke, the top of the stroke, or something else? Also, if the engine is running at 600 rpm, isn't there an ignition stroke every 300 rpm?

Any techies out there want to tackle this?

------------------
Alan Hepburn - F450 CC PSD 2WD 4R100 XLT+


Van
Member
Member # 416
Reged: 04/05/99
Posts: 4
Re: FUEL CONSUMPTION AT IDLE new
#181857 - 04/08/99 05:06 PM

I don't know the right answer but I know 164.25 l/hour is way WRONG. AT 60 MPH and a conservative 10 MPG, you are only burning 22.74 l/hour. That 200:1 ratio is off I believe. Perhaps that ration is for oxygen. But the atmosphere is only 7% oxygen (that's a guess). That would bring the answer down to 13.69 l/hour. Also, at 600 RPM there are only 300 ignition revs which makes it 6.84 l/hour. Still seems high, though. Good question.

powerchoke
Member
Member # 217
Reged: 04/02/99
Posts: 194
Loc: Toddville, IA, USA
Re: FUEL CONSUMPTION AT IDLE new
#181858 - 04/08/99 05:43 PM

I don't think that the fuel/air ratio is accurate. I think that it is much much greater than that.

Plus, Doug's calculation was off by a factor of two. Since there is only one intake stroke per 2 revolutions.

TDC-BDC Intake stroke
BDC-TDC Compression stroke
1 rev complete

TDC-BDC PowerStroke
BDC-TDC Exhaust stroke
2nd rev complete - one complete cycle

To estimate the fuel/air ratio I calculated the amount of volume of air mixed with fuel at 60 miles per hour. I estimate my fuel mileage at 60 mph to be 18 at 2000 rpm (I can't remember what rpm's I'm at exactly but this will work for an estimate). So, I can calculate the total volume that goes through the engine and I know the amount of fuel so I can then determine the ratio. This will be off somewhat due to the turbo compressing more air than would fit by a naturally aspirated engine but it's the best I can do.

So I get:

60mi 1 gal 1L
--- x ----- x ---------
1hr 18mi 0.264 gal

= 12.62 L/hr -> 12.6L of fuel is consumed in 1 hour.

Now to determine the total volume in 1 hour:

2000rev 1 intake stroke 60 min
7.3L x ------- x --------------- x ------
1 min 2 revolutions 1 hr

= 2000 x 30 x 7.3L/hr

= 438,000 L/hr -> 438,000 L of air and fuel in one hour

438,000 - 12.6 =~ 437988 L air / hour

ratio then is approx 438000/13 = 34,000 to 1

so now for 600 rpm's:

600rev 1i.s. 60min
7.3L x ------ x ------- x ------
1min 2 rev 1hr

= 131,400 L/hr

Fuel to air -> 131,400 / 34000 = 3.8L/hr

3.8L <=> 1 gal

This is much more reasonable than 164L/hour PER cylinder but still seems a little high. Considering my crude rounding , neglecting the compression of the turbo at 2000 rpm, estimation of fuel mileage at 60 mph, estimation of rpm's at 60 mph AND that the fuel/air ratio is probably different at 600rpm than at 2000 it's likely that more accurate figures would yield a more accurate result.

Of course I am probably way off here with my formulas and it may be purely coincidence that I arrived at a result that seems more probable. Take it for what it's worth I guess.


Doug J
Member
Member # 9
Reged: 04/01/99
Posts: 377
Loc: Vancouver, Washington, U.S.A.
Re: FUEL CONSUMPTION AT IDLE new
#181859 - 04/08/99 06:36 PM

Guys,
You couldn't have possibly taken my calculations seriously! I can't even balance a check book. If you really want to figure this out, I think you had better start with Powerchoke's numbers.

------------------
Doug J
Washington State
99 F350 4X4 SC LB 6spd



johnmModerator
Administrator
Member # 199
Reged: 04/02/99
Posts: 2110
Loc: Las Vegas, Nevada
Re: FUEL CONSUMPTION AT IDLE new
#181860 - 04/08/99 09:08 PM

Think you've missed the most important part, how much the injector squirts in each intake cycle. I'm sure that it is controlled by the computer and is different depending upon rpm, altitude, temperature of the fuel and outside air, etc. I've asked Brent at DIS to help out on this as it is a very interesting topic and his input should help us figure it out.

------------------
johnm 99.5 F250 XLT PSD SC LWB 4R100 3.73LS 4ABS
johnm@me.unlv.edu




mike g
Member
Member # 25
Reged: 04/01/99
Posts: 2050
Loc: Fond du Lac WI.
Re: FUEL CONSUMPTION AT IDLE new
#181861 - 04/08/99 09:12 PM

Hey Doug if it makes you feel any better I didn't take you seriously.

------------------
F-350 PSD 4X4 CC LB Duelly 4.10 AUTO



smart
Member
Member # 44
Reged: 04/01/99
Posts: 126
Loc: FORT LAUDERDALE, FL
Re: FUEL CONSUMPTION AT IDLE new
#181862 - 04/08/99 09:14 PM

Hi Guys

will e-mail navistar tech support v8 dept now
and try to get a real answer..

Then will post it

From steve
Fleet


Jim M
Member
Member # 214
Reged: 04/02/99
Posts: 94
Loc: No. Brookfield,Ma.
Re: FUEL CONSUMPTION AT IDLE new
#181863 - 04/08/99 09:40 PM

I received a "performance prediction" on a truck we are building at work the other day on a Navistar DT466 (+22 cubic inches) and the sheet had on it "idle fuel rate: 0.37 gals/hr @ 700 rpm". So take a little off for a little less rpm and 22 less cubic inches, I would say around 0.30 gal/hr. ????

Jim

99 F-250 SD PSD 4X4 SWB SRW

islander
Member
Member # 479
Reged: 04/06/99
Posts: 106
Loc: So. Cal
Re: FUEL CONSUMPTION AT IDLE new
#181864 - 04/09/99 12:15 AM

So John's 1-2 quarts per hour estimate is quite accurate, I was so worried about my wife's Mercedes at the begining, it's 14 to 1 air fuel mixture could mean 15 times more consumption of gas with the same calculation.

Eric

Brent - DIS
Sponsor
Member # 347
Reged: 04/04/99
Posts: 500
Loc: Lubbock, TX
Re: FUEL CONSUMPTION AT IDLE new
#181865 - 04/09/99 01:44 AM

Sorry to let you down John but some of these guys are going way over my head (and thats not a very long journey) - Randy our service mgr would know the answer but since I will be out of town I will not be able talk to him till Monday..

Steve seems to have the best idea though
Calling Navistar Tech Support

Brent
DIS

Roger
Member
Member # 594
Reged: 04/09/99
Posts: 2
Loc: Bismarck, ND
Re: FUEL CONSUMPTION AT IDLE new
#181866 - 04/09/99 08:22 PM

Forget the math, I had to idle my 97 PSD last winter a couple of evenings when at a motel when all the plug-ins were taken. I idled at 650 rpm's in outside temps of -25F to -35F using #1 fuel. Thanks to duel tanks the calculation is clean. Average consumpion 1.8 hours/gallon. I suspect it would be higher at warmer temps and using #2. I will let you guys figure that one out.

Roger
Member
Member # 594
Reged: 04/09/99
Posts: 2
Loc: Bismarck, ND
Re: FUEL CONSUMPTION AT IDLE new
#181867 - 04/09/99 08:36 PM

P.S. Thats .55 gallons/hour

islander
Member
Member # 479
Reged: 04/06/99
Posts: 106
Loc: So. Cal
Re: FUEL CONSUMPTION AT IDLE new
#181868 - 04/11/99 11:52 PM

Considering the cold ambient temperature and #1 diesel, .55 gph sounds fine, but aren't you supposed to rev it up a bit higher than 650 rpm to prevent the dilution of lube oil?
In So.Cal our need to keep the engine running is to cool the cab like tour buses in the hot weather, wonder if the dilution at idle is more of a problem for the hot or cold weather?

99.0 4x4 drw cc

Joe Asciutto
Member
Member # 263
Reged: 04/02/99
Posts: 5
Loc: San Diego, CA, USA
Re: FUEL CONSUMPTION AT IDLE new
#181869 - 04/12/99 12:21 AM

This isn't an exact comparison by any means, but it something to think about. In 1981 I bought a Datsun diesel pick-up, and at one of their sales promotions, they (Datsun) had one of their engines idle for over 6 hrs on a gallon of fuel. As I remember, the point that they were trying to get across was that a diesel engine uses VERY little fuel at idle and therfore is great for stop & go driving. We were instructed that a diesel only needs enough fuel at idle to overcome the internal friction of the engine plus any accessories that it is running, unlike a gas engine that must maintain an air fuel ratio close to 14.7 to 1 in order to run. Remember you can't run a diesel too lean like you can a gas engine.

Pages: 1



Contact Us TheDieselStop.Com

*
UBB.threads™ 6.3


All trademarks and copyrights on this page are owned by their respective companies.
All else is Copyright 1997-2003 TheDieselStop.Com.
All Rights Reserved

TheDieselStop.Com Privacy Statement
Advertising on TheDieselStop.Com

This site is in no way affiliated with Ford Motor Company or International Truck and Engine Corporation.