Beam-break sensors for ignition delay measurement

In summary, the project supervisor has asked the student to make an apparatus in which the ignition delay of fuel droplets could be measured. The student has been researching options and has found that photointerrupters in reverse bias have high resistance and that the resistance decreases when light falls upon them. The student is wondering how the change in resistance could be used to trigger a stop watch. The student will likely need to make his own components because the temperature and pressure requirements for the project are too high for simple production photointerrupters.
  • #1
saguntripathi
1
0
Hi all..

I have been working on a project which involves the measurement of ignition delay of fuel droplets using optical sensors of the beam-break type. What my project supervisor has asked me to do is to fabricate an apparatus in which such measurements could be made. The basic principle would be to trigger a stop watch as soon as the beam of the sensor is intercepted by a fuel droplet and stop the timer as soon as ignition takes place.

Being a student of mechanical engineering I do not have much knowledge of sensors and other electronic circuit components. I have been browsing the internet for a while now looking for sensors and the suitable circuit that would be required in this case. During my search I also found out that photodiodes in reverse bias have very high resistance and their resistance decreases when light falls upon them. I was wondering how could this change in resistance be utilized for triggering a stop-watch.

Can anyone suggest a possible circuit design for measuring the ignition delay?
The operating temperatures and pressures would be quite high and so the sensor should be able to work in those conditions as well.
It would be nice if anyone could help. Thanks
 
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  • #2
Wecome to PF.
I hate to see you sitting here all by yourself, but I can't help. There are, however, people here who can. I'm sure that one of them will be along shortly.
 
  • #3
Here is a selection of Photointerrupter circuits from Digikey. Select some simplifying terms in the menus, and click on "Apply Filters":

http://www.digikey.com/scripts/dksearch/dksus.dll

But, your temperature requirements are going to likely be too high for simple production photointerrupter components, so you will likely need to make your own from LED and a PIN Photodiode, both somehow housed outside of the fuel droplet path (both to isolate them from the high temperatures, and to make sure that they don't interfere with the combustion process (standard photointerrupters are not intrinsically safe devices).


This wikipedia.org article will start to give you some background on the operation of a photodiode:

http://en.wikipedia.org/wiki/Photodiode

You will likely want to have a fast responding circuit, so that means using a photodiode (not a phototransistor or other photosensor), in reverse bias in a fast current-to-voltage circuit, like figure 13 here:

http://en.wikipedia.org/wiki/Current-to-voltage_converter
 
  • #4
best way is to use a laser can be cheap (HeNe) and have a photo detector on the other side. Then you put the input of that detector into a fast data acquisition system (GageScope is great) LabView is also good. You can also use a stand alone digital oscilloscope although they are a little less user friendly and sometimes a little more expensive. Anyway, this is the way we measure spray and droplet durations in shock-tubes, also, onset of ignition can easily be measured using a photo detector (PMT) in combination with the right filter (OH* at 310 nm and CH* at 430 nm). Please let me know if you have any specific questions because I am pretty familiar with these kind of setup.
 

Related to Beam-break sensors for ignition delay measurement

1. What is a beam-break sensor?

A beam-break sensor is a device that uses a light beam to detect when an object passes through it. It typically consists of an emitter and a receiver, with the emitter emitting a beam of light and the receiver detecting when the beam is interrupted.

2. How is a beam-break sensor used for ignition delay measurement?

A beam-break sensor can be used in conjunction with a fuel injector to measure the ignition delay of a fuel. When the fuel is injected into the sensor's light beam, the beam will be interrupted. The receiver will then detect the interruption and send a signal to a data acquisition system, which can measure the time between the fuel injection and the interruption of the beam. This time interval is known as the ignition delay.

3. What are the advantages of using beam-break sensors for ignition delay measurement?

One advantage is that beam-break sensors are non-intrusive, meaning they do not physically interact with the fuel being measured. This allows for more accurate and repeatable measurements. Another advantage is that they are relatively inexpensive and easy to use, making them a popular choice for ignition delay measurement.

4. Are there any limitations to using beam-break sensors for ignition delay measurement?

One limitation is that the accuracy of the measurement is dependent on the size and shape of the fuel droplet passing through the sensor's light beam. This can vary depending on the type of fuel being measured. Additionally, the sensor's performance may be affected by ambient lighting conditions, so it is important to control for these factors during measurements.

5. Can beam-break sensors be used for other types of measurements?

Yes, beam-break sensors can be used for a variety of applications besides ignition delay measurement. They are commonly used in industrial settings for object detection, counting, and sorting. They can also be used in laboratory settings for measuring particle size and velocity, as well as in wildlife studies for tracking animal movements.

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