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# Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/09/2014 2:57 PM

Hi,

I want to measure the exhaust gas energy. However, I have just one temperature sensor OUTSIDE the exhaust pipe, and a hall sensor to measure the speed of the vehicle, is there a way to measure the exhaust gas energy by making some approximations on the gas flow rate and the temperature of the gas inside?

Assume we know the specific heat capacity of the gas.

For the approximations I want to know if the following concepts are true :

1. We can calculate the mass flow rate from the the air-fuel ratio and miles per gallon.

2. The mpg is a function of the speed of the vehicle (which is measured by the hall sensor).

3. The temperature of the gas inside the exhaust pipe can be found by the temperature on the outside of the pipe and the heat transfer coefficient of the pipe.

Any ideas?

Pathfinder Tags: Energy exhaust gas heat Measure
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#1

### Re: Measuring Exhaust Gas Energy without sensor inside the pipe

07/09/2014 3:23 PM

Wow...

If I felt compelled to conduct such a survey, I think I would

1) Discover efficiency of the ICE
2) Discover fuel consumption rate
3) Do the maths

The temp of the exhaust... an undefined distance from the source, transferred thru a pipe of unknown dimensions, operating in an unknown ambient temperature, with some unknown heat radiation rate thrown in for good measure... what will that number mean?

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#2

### Re: Measuring Exhaust Gas Energy without sensor inside the pipe

07/09/2014 3:58 PM

A Hall effect sensor measures magnetic fields. So unless your hall effect sensors measure the wheel rotation rate from a magnet spinning on a wheel, you will not know anything about velocity. You will also have to take the derivative of your Hall effect reading to obtain any data that remotely correlates to vehicle velocity. You also assume an awful lot of uncertain information for the basis of any kind of calculation. The outside surface temperature of your exhaust pipes will not correlate fast enough with the inside gas temperature if the correlate at all. The outside surface temperature will change with ambient air temperature along with air flow from movement turbulence and convection. Not to mention the thermal conductivity time constant of the pipe material.

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#3
In reply to #2

### Re: Measuring Exhaust Gas Energy without sensor inside the pipe

07/09/2014 6:12 PM

......not to mention fuel quality consistancy

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#4

### Re: Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/09/2014 6:43 PM

What folly!

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#5

### Re: Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/10/2014 8:57 AM

All you are going to measure is the temperture on the outside of your exhaust system.

It will be up to you to do the conversions with the correct assumptions on all the other missing parts.

But why on Earth would you like to do this?

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#6

### Re: Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/10/2014 7:26 PM

"I have just one temperature sensor OUTSIDE the exhaust pipe"

Is it:

1. OUTSIDE the exhaust pipe under the hood?

2. OUTSIDE the exhaust pipe under the car?

3. OUTSIDE the exhaust pipe behind the car? 1 inch away? 5 inches away? Is the wind blowing? How will this sensor work at 60 MPH?

4. OUTSIDE the exhaust pipe down the street?

5. OUTSIDE the exhaust pipe in the next city?

You see where this is going, don't you?

Nowhere!

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#7
In reply to #6

### Re: Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/10/2014 10:31 PM

Your point 5. Sounds about feasible to me. Its the same way we determine global warming. I would put the sensor there if I was OP!

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#8

### Re: Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/11/2014 12:08 PM

That's okay. The moderators can delete this thread.

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#9
In reply to #8

### Re: Measuring Exhaust Gas Energy Without Sensor Inside The Pipe

07/13/2014 10:36 PM

I don't think that is going to happen. It will be a fine example of the things that are getting posted in the internet without the option to back off again.

With speech it is: think before you talk, with the internet it is think twice before you type.

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