Generating a short duration spark

In summary: BOBthanks for the help. one more question. in the traditional ignition circuit, what is the primary coil? is it the one with the higher voltage?
  • #1
percy1
2
0
Hi

I'm trying to build a system to generate a spark with sufficient energy to ignite a freely expanding jet of methane, but with a quite short duration, ca. 20ms (if that is classed as short?) The purpose being to examine concentration fluctuations of gas (in a jet) above and below the flammability limits due to turbulence. I have pretty limited experience of electronics so am I hoping for some guidance, primarily so I have confidence in what I am doing, and am not going to do my self an injury.

From some internet research i think the way to go is to use a car ignition coil connected to a car battery, then the high voltage wire coming off the coil will spark with a suitable ground when the low voltage circuit is completed and then broken. Does this sound right? Are there any other components that i should have?

With a system like this how do you control the spark duration? Does varying the spark gap does this? (To keep the expt’s relevant I need to have a gap below 2/3mm), And also how can I determine the spark duration?

Any guidance or references to textbooks on this subject would be much appreciated

percy
 
Engineering news on Phys.org
  • #2
Here is a traditional (before transistors) automobile ignition circuit:

https://www.physicsforums.com/attachment.php?attachmentid=20126&d=1250393723

A 2 mH ignition coil (with 12-ohm internal resistance) is in series with a 0.02 uF capacitor in parallel with a switch to ground. When the switch opens, a 300-volt pulse is generated across the coil primary. With a 1:100 turns ratio, the coil secondary develops a 30 kV spark a fraction of a millisecond long. Note: the 300-volt pulse is also generated across the capacitor and the switch.

Bob S
 
  • #3
Bob

thanks for your help. one or two more question if that is ok. How can i vary the spark duration, does the switching play a role in that? And also if i wanted to automate the circuit to spark every couple of seconds what kind of components would achieve that?

ta
percy
 
  • #4
The high voltage oscillation frequency in the circuit

https://www.physicsforums.com/attachment.php?attachmentid=20126&d=1250393723

is proportional to sqrt(1/LC), where L and C are the inductance and capacitance in the circuit. The pulse duration is proportional to exp[-Rt/L], where t= time in seconds, and R is the total circuit resistance. Once a spark occurs (usually on the first half cycle), the oscillation is quenched. To fire the circuit every couple of seconds, a NE555 timer could be used as a timing source, but the switch would have to be able to open (switch 1 amp) quickly, and the open-switch hold-off voltage would have to be over the coil primary voltage (~300 volts). (Note in above circuit that the high voltage occurs when the switch opens).

An alternative is to get an old CD (capacitor discharge) ignition circuit, which uses a dc-dc converter to charge a capacitor to ~300 volts, and uses an SCR to discharge it into an ignition coil. These could be triggered directly by an NE555. Some old CD ignition modules are available on eBay (they were popular 1965 to '75) (Mark Ten is a good brand), and new ones are available in automotive supply stores (very $$$).

Bob S
 

1. How does a spark generate a short duration spark?

A short duration spark is generated by applying a high voltage to a small gap between two electrodes. This high voltage creates an electric field that ionizes the air molecules in the gap, causing them to conduct electricity and create a spark.

2. What materials are needed to create a short duration spark?

The main materials needed to create a short duration spark are a source of high voltage, two electrodes, and a small gap between the electrodes. Other materials that can be used include a power supply, a capacitor, and a resistor.

3. How can the duration of a spark be controlled?

The duration of a spark can be controlled by adjusting the voltage, the gap between the electrodes, and the materials used. A higher voltage, smaller gap, and more conductive materials will result in a shorter duration spark.

4. What are the main applications of short duration sparks?

Short duration sparks have many applications in scientific research, such as in high-speed photography, plasma generation, and electric discharge experiments. They are also used in industrial processes, such as welding and ignition in internal combustion engines.

5. Are there any safety precautions to take when generating a short duration spark?

Yes, there are several safety precautions to take when generating a short duration spark. These include wearing protective gear, working in a well-ventilated area, and using appropriate voltage levels to avoid electric shocks or fires. It is also important to follow proper equipment handling and storage procedures.

Similar threads

  • Electrical Engineering
Replies
22
Views
5K
  • Mechanical Engineering
Replies
7
Views
2K
  • Electrical Engineering
2
Replies
36
Views
21K
  • Mechanical Engineering
Replies
17
Views
2K
  • Other Physics Topics
Replies
1
Views
905
Replies
18
Views
3K
Replies
1
Views
829
  • Electrical Engineering
Replies
5
Views
3K
  • Electrical Engineering
Replies
5
Views
3K
  • Electrical Engineering
Replies
1
Views
2K
Back
Top