Rate of Gas Use

[GCAdidas13 10+ year member]

I have a question.

I know that the RPM of a vehicle in drive coorelates directly to the amount of gas used. (ex: you use gas twice as fast at constant 1400RPM as you do at constant 700RPM)

What about 700RPM in drive vs. 700RPM in park? How much gas, relatively, does a parked car use vs. a car in drive at the same RPM?

I ask because I am thinking about turning up the idle of my car, but the nature of my work (pizza delivery) requires my car to be parked while on for 10-15 minutes at a time.

Let me know!

Brian

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[GCAdidas13 10+ year member]

alright i notice that there are no squared terms in the equation, so therefore RPM to fuel consumption would be linear, correct?

so therefore increasing my idle to around 900-1000 rpm's would use up that much more gas during idle.

 

[GCAdidas13 10+ year member]

so i make anywhere from 10-20 delivery trips every night i work. i'm told that it would be best to just leave the car on to save the engine from the wear of starting up 10-20 times per night.

how damaging is it to start a car 10-20 times per night?

 

[SSS 18734 5,000+ posts]

only thing that would wear out faster is the starter, really. Oil doesnt drain completely from the engine in only 10 minutes.

 

[GCAdidas13 10+ year member]

Increasing idle from 700 RPM to 900 RPM would increase fuel consumption by 900/700 = 1.286 (28.6%) ...

1.) does this mean that whe car is in drive with no throttle input, it will have a higher idling speed? (just so i understand how it works)

2.) does this mean that just at idle i will use 30% more gas, or through the entire spectrum i will use 30% more gas?

only thing that would wear out faster is the starter, really. Oil doesnt drain completely from the engine in only 10 minutes.

3.) and starters probably have a set amount of times that they will work until it burns out... or do they usually work well until time takes it's toll on it? or is it a mixture of the two?

 

[vosschs 5,000+ posts]

i always wanted to know how do they measure the liters in the vehicles engine?

 

[Acidburn 5,000+ posts]

i always wanted to know how do they measure the liters in the vehicles engine?

the volume of each cylinder * number of cylinders = total internal volume

 

[GCAdidas13 10+ year member]

okay how about 2.2L engine operating at 1000RPM at idle?

 

[GCAdidas13 10+ year member]

Thanks Jmac //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[vosschs 5,000+ posts]

ya thanks acid and jmac

 

[GCAdidas13 10+ year member]

is the A:F ratio of 14.7 the average characteristic? What does that depend on?

and i would assume that a 700RPM idle would be .6153mL/sec and last about 1.7 hours per gallon, assuming the same A:F ratio.

 

[GCAdidas13 10+ year member]

i guess what i'm trying to ask is how accurate is the equation when three values have to be estimated - like FD, AD, and AFR from your first post

just askin

 

[GCAdidas13 10+ year member]

gotcha; thanks for all the help

 

[Alpineinstaller 10+ year member]

Let's bust out the old formula here ...
mL/s =(CC*(RPM/240)*(1-((AFR/AD)/((AFR/AD)+(1/(FD*1.25))))))

mL/s = mL of fuel used per second

CC = engine displacement in cubic centimeters

RPM = engine speed in revolutions per minute

AFR = Air to fuel ratio

AD = Air density in kilograms per cubic meter

FD = Fuel density in grams per liter

The things that affect fuel consumption are:

Engine displacement

Engine speed

Air:Fuel Ratio (throttle input)

Assuming no throttle input, there should be no difference between 700 RPM in Park and 700 RPM in Drive ...

BTW, you should turn your car off whenever you plan to be stopped for more than 30 seconds ...

JMAC is a genius

 

[GCAdidas13 10+ year member]

BTW, you should turn your car off whenever you plan to be stopped for more than 30 seconds ...

Honestly? Even in my scenario, delivering pizzas and stopping 5-20 times per night?

Thanks

Brian