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Old 02-12-2006, 09:22 PM
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Question Any automotive engineers in here? or automotive math people

i have a automotive question for one of my classes envolves finding out air volume air mass fuel consumption and some other things seeing if anyone thinks they would know the answers if your good i will post the problem thanks!
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Old 02-12-2006, 09:39 PM
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Why not just post the question?
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Old 02-12-2006, 10:51 PM
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air at sea level at 70 degrees is~.08 lb/ft3. add fuel density in percentage. You can find fuel usage on some older dyno runs. Pose the question and lets have at it!
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Old 02-13-2006, 03:14 PM
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Question heres the problem

one cylinder engine dynamometer
operate the engine at 1200 1500 1800 RPM the throttle should be wide open. Control the engine speed withtthe load adjustment.Record the air volume at each RPM. Calculate the fuel mass needed for 13:1 ratio. Run engine at each RPM and adjust the fuel to correct ratio and check the torque. show how toy solved calculate brake specific fuel consumption and brake specific air consumption.

13:1 ratio
WOT air volume Fuel mass/grams Torque
RPM
1200 60
1500 70
1800 78
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Old 02-14-2006, 01:13 AM
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What is the displacement or bore/stroke? 2 or 4 stroke? Throw us a friggin bone here!
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Old 02-14-2006, 09:14 AM
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small 4 stroke engine
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Old 02-14-2006, 01:41 PM
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Default Ok what about ???

Hi 73_RoadRunner;

Need some more variables Normally asperated or supercarged. Air Density, Specific gravity of fuel, Octane rating, Timing set or is that variable also, The engine is air cooled or water cooled. Is the metal aluminum, iron or steel alloy. Is engine cam timing set or is it variable, what is bore vs stroke, undersquare, oversquare, or square. Also is it miller cycle, otto cycle, Diesel cycle ( diesel is a supercharged two stroke, auto ignition ) If you want numbers out of this we'll need a lot more info...

Denny
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Old 02-15-2006, 08:34 AM
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13 times the fuel rate (has to be grams/time) will give you the weight of air. Convert grams to lbs. Then use the density to find the cubic volume of air.

You haven't given us the torques at each rpm.
You need those torques to convert to horsepower, then convert to horsepower-hrs (which is energy)

Brake Specific Fuel Consumption (brake is just an old word for dyno)

BSFC= (lbs of fuel used per hour)/(average horsepower over an hour)

If you are actually doing that stuff in a lab with a real CFR single cylinder engine - you are lucky!

Most students today don't get to run real engines in labs anymore.

My grandfather helped design that variable compression ratio single cylinder engine - if it is the common CFR type (Council of Fuel Research)

If anyone is interested in seeing one of those engines run, call whatever state agency tests gasoline octane and checks pumps for accuracy in the gallons readout. (in NC it is the agriculture dept in Raleigh)
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Old 02-15-2006, 12:32 PM
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Default In oil Refineries

Hi All;

In oil refineries, the testing labs have a test engine. Its a one cylinder variable compression engine. Iso octane (8 sided hydrocarbon) which rated for 108 motor octane, then other gasolines are run to compare against iso octane. Over simplified but basically correct...

Denny
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Old 02-15-2006, 02:31 PM
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Default mega tech

one cylinder engine dynamometer
operate the engine at 1200 1500 1800 RPM the throttle should be wide open. Control the engine speed withtthe load adjustment.Record the air volume at each RPM. Calculate the fuel mass needed for 13:1 ratio. Run engine at each RPM and adjust the fuel to correct ratio and check the torque. show how toy solved calculate brake specific fuel consumption and brake specific air consumption. fuel used per minute too for the ratio
wet bulb 60 dry 73 baro 31.1 engine 4 stroke glass piston vapor pressure chart came out to .38

13:1 ratio air lbs
air vol cfm mass Fuelmass fuel/grams Torque Cor fact Hp BSFC BSAC fuel used per minute
RPM
1200 60 1 .075 .0058 2.58 =25cm 11 10.4808 2.39 .1457 1.88
1500 70 1.67 .087 .0067 2.97 =30cm 8.5 8.0988 2.31 .1735 2.26
1800 78 1.3 .0975 .0075 3.33 =33cm 7 6.6696 2.28 .1971 2.57





can some one check my work from starting with just few things you have to know to start out thanks
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Old 02-16-2006, 12:08 AM
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This is what they are teaching nowdays? I thought it would be engine management software programming or something like that. Thats some good stuff! I remember V8's on rolling cradled that we had to take apart to bearing halves and reassemble in 2 hours with no pneumatics for our final. We didnt have any 4 or 6's.
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Old 02-16-2006, 06:04 AM
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73 Roadrunner,

I am having trouble reading the table's columns to know which number matches a value like Torque, correction factor, horsepower, etc,
but the BSFC looks too high at +2 when I would expect it to be in the range of 0.35 to 0.7 (lbs/hp-hr)

I am also a bit concerned that there is a mistake because your HP is going down as the RPM goes up? That seems wrong if the throttle is wide open.....

It would help if you could edit your post
and label the columns in the table
against the numbers below them
to make it more certain which numbers are under which title.
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Old 02-16-2006, 12:21 PM
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Question confused

i guess now im just confused with this testing can anyone give me there readings from just the least info needed like air volume baro dry wet bulb so i can figure out what i did wrong
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