What is the average Idling gas consumption in a 3A engine?

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Dumindu
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What is the average Idling gas consumption in a 3A engine?

Post by Dumindu » Tue Aug 06, 2019 10:29 pm

Does anyone know the average Idling fuel consumption rate of a Tercel 1500CC 3A engine ?
(Liters per Hour /Gallons per Hour at 700 rpm)

Note:
My car had a poor gas mileage due to maladjustment of the carb. After correct that I want to check whether the present situation is ok. So I need the standard value to compare.
Last edited by Dumindu on Wed Aug 07, 2019 7:13 pm, edited 1 time in total.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Ellisdee » Wed Aug 07, 2019 12:33 pm

Pretty easy to check...use a one liter container full of gas, disconnect the fuel line at the filter...stick it in the container and time how long it takes...half a liter would work too, if one liter takes too long.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Petros » Thu Aug 08, 2019 12:57 am

you might be able to estimate it by doing a calculation:

taking the displacement, divide by 2 (four stroke engine), multiply by the RPM. that gives you volume/min. typical idle air/fuel ratio is about 12 to one (by weight). take the weight of the air, and than you get the weight of the fuel consumed per min. than you convert to volume of fuel.
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Re: What is the average Idling gas consumption in a 3A engine?

Post by Dumindu » Thu Aug 08, 2019 10:42 am

Thank you very much.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by NWMO » Thu Aug 08, 2019 12:19 pm

Dumindu,

From an internet search, smaller gas engines should roughly burn 1/6 gallon of fuel per hour while idling. Thus, 0.5 liters should idle for 50 minutes, 0.25 liter should idle for 25 minutes, etc. I have never tested the Tercel, so I can't say if this is a good approximation or not.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Dumindu » Fri Aug 09, 2019 4:42 am

Based on the Calculations:

Since the engine capacity is 1.452 l and Since 2 of the 4 cylinders have intake strokes in a one cycle,

one cycle(round) draws 1.452x0.5 l = 0.726 l

So at 700 rpm, it draws 0.726x700 =508.2 l volume per minute.

Since density of the air fuel mixture is nearly equal the density of air and the air density is 1.29 g/l

Above volume weights 508.2x1.29 = 655.58 g = 0.6556 kg

Since one thirteenth of it is petrol (if the air fuel mixture is 12:1), petrol weight is 0.6555/13 =0.05043 kg.

Since petrol density is 1.4 l/kg, Petrol volume consumed at a minute is 0.05043x1.4=0.07 l

That means 0.07x 60 = 4.2 litres per hour.

So it is nearly one gallon per hour !
Last edited by Dumindu on Fri Aug 09, 2019 7:58 pm, edited 1 time in total.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by NWMO » Fri Aug 09, 2019 7:28 am

Dumindu,

I would expect your calculations are off by roughly a factor of two (which is likely closer than my internet search). I don't see the math error, but expect the 12:1 air/fuel ratio is by mass, not volume.

I know my cars gets approximately 26 mpg on the highway. Driving 60 mph (roughly 2,900 rpm), the 26 mpg translates to 2.3 gallons/hour. Assuming a roughly linear correlation between fuel use and rpm (2,900rpm/725rpm=4), idle consumption should be roughly 2.3/4 = 0.58 gph. Converting to liters provides roughly 2.1 liters/hour while idling.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Dumindu » Fri Aug 09, 2019 12:56 pm

Mr.Chris,

Thank you very much for your detail.

Now my car uses up 1.2 l per hour at idling. It seems my car fuel economy is very good now.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Petros » Fri Aug 09, 2019 4:05 pm

Dumindu,

you calculation is off by a factor of two because you multiplied displacement by RPM, it is only one intake stroke per TWO revolutions (four stroke engine, one power cycle per two revs).

the 12:1 air fuel ratio is a guess, it ranges from about 11 (on hard acceleration) to as lean as 16:1. the "ideal" air/fuel ratio is 14.7:1 (all oxygen consumed to all fuel).

thou even at about 2 L per hour seems high, perhaps there are other errors? that is about what you should burn per hour driving at 50 KPH.
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Re: What is the average Idling gas consumption in a 3A engine?

Post by teranfirbt » Tue Aug 13, 2019 9:06 am

The math is off because the density of air going into the engine at idle is about 1/3 atmospheric conditions, or about 0.4 g/l of air :-)

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Mattel » Tue Aug 13, 2019 4:55 pm

Petros wrote:
Fri Aug 09, 2019 4:05 pm
Dumindu,

you calculation is off by a factor of two because you multiplied displacement by RPM, it is only one intake stroke per TWO revolutions (four stroke engine, one power cycle per two revs).

the 12:1 air fuel ratio is a guess, it ranges from about 11 (on hard acceleration) to as lean as 16:1. the "ideal" air/fuel ratio is 14.7:1 (all oxygen consumed to all fuel).

thou even at about 2 L per hour seems high, perhaps there are other errors? that is about what you should burn per hour driving at 50 KPH.
hey Petros, There is no way our cars would be consuming 4L per 100km (standard measurement for fuel economy in metric countries) the Tercel averages 8 to 10L of petrol per 100kms normally.
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Re: What is the average Idling gas consumption in a 3A engine?

Post by Petros » Tue Aug 13, 2019 9:37 pm

Mattel,

I do not have good feel for metric fuel economy measurements, it seems an odd way to measure it for me. in miles per gallon it is easy to estimate how much further you can drive on say half or a quarter tank. Km per Liter seems way more useful, but metric countries have no idea what that is. So, I know I have 22 liters left in my tank, how far can I go before I need to stop and get fuel?

Anyway, i was talking about liters per hour at idle, 2L/hr would be about a half gallon an hour. The way my MPG mind thinks is: in gallons, that would be worth about 15 miles, at a typical 30 mpg for a Tercel, a half hour worth of driving. It does seem that burning 2 L an hour would be too much for idle. it would be about the same as driving at 15 mph, or perhaps 25 kph (so my original reckoning was off).

would not 1 L per hour at idle make more sense?
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Re: What is the average Idling gas consumption in a 3A engine?

Post by teranfirbt » Wed Aug 14, 2019 2:06 pm

Doing the math out for 700 RPM idling and 33 kpa Manifold pressure gives about 1.1 liters per hour.

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Re: What is the average Idling gas consumption in a 3A engine?

Post by Dumindu » Mon Aug 19, 2019 8:11 am

Thank you very much for your advice.

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