Making hot electric sparks - Page 1
Forum section: electronics / projects

author: king.oslo
author_rank: Frequent Contributor
timestamp: June 01, 2014, 04:13:43 pm
content: Hello there,I am an undergrad physics student.Electric sparks are used to ignite fuel. That must be because sparks radiate heat energy. How can I make a spark really hot? What makes some sparks radiate a lot of energy, whilst others radiate less? Is the energy released proportional to the current, or are there other factors involved in making a spark very energetic?Thank you for your time.Kind regards,Marius

author: Phantomix
author_rank: Contributor
timestamp: June 01, 2014, 04:23:54 pm
content: It's all about the U (Voltage) and the I (Current). You get "bigger sparks" with more U, while the I depends on the medium where the spark goes through. What do you want to ignite?An easy way to reproducibly get "sparks" would be to use the same things you find in a vehicle, an ignition coil and spark plug...

author: w2aew
author_rank: Super Contributor
timestamp: June 01, 2014, 04:51:03 pm
content: In general, higher voltage makes larger/longer sparks (think van de graff generator). Higher current makes hotter sparks (think arc welder).

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 01, 2014, 05:27:58 pm
content: What you need is to increase the peak power of the spark. A common approach is to boost the 12V to some intermediate voltage like 300-400V, then use that to drive a forward converter in order to provide the 30kV or so needed to make the spark. With a higher primary voltage, stray inductance and resistance matters less so the power can be delivered very quickly. (Look up "pulsed power" to understand this better.)Some argue that a "hotter" spark provides no improvement, but that's not true. A hotter spark can get the mixture ignited faster (higher RPM and thus more horsepower) as well as ignite leaner mixtures (better MPG). The 2011 Hyundai Sonata was the first mainstream car to make use of that double converter architecture and its 35 MPG highway rating was considered very good for its time.

author: babysitter
author_rank: Frequent Contributor
timestamp: June 01, 2014, 05:38:06 pm
content: In the case of "DC" sparks, remember there is one hotter electrode than the otherm dont ask me now which one:)

author: c4757p
author_rank: Super Contributor
timestamp: June 01, 2014, 05:42:33 pm
content: Quote from: babysitter on June 01, 2014, 05:38:06 pmPositive, surely? It has to absorb the kinetic energy of the electrons.

author: G7PSK
author_rank: Super Contributor
timestamp: June 01, 2014, 05:57:18 pm
content: All the oil burners that I have taken apart just use a transformer driven from the mains, somewhere in the region of 10 to 20 watts. the out put in the region of 12 KV.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 01, 2014, 06:05:13 pm
content: It's about the arc current. You need a high initial voltage to break the air down, but once struck, the important thing is how much current is available. e.g. putting a small amount of capacitance on the output of a Jacob's Ladder makes much louder & cracklier sparks.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: June 01, 2014, 07:28:36 pm
content: Quote from: NiHaoMike on June 01, 2014, 05:27:58 pmConservation of energy: Physics 201 (W = I * V )Quote from: c4757p on June 01, 2014, 05:42:33 pmWhen DC TIG welding, heat goes into the work which is connected to the positive lead.

author: IanB
author_rank: Super Contributor
timestamp: June 01, 2014, 08:10:57 pm
content: Quote from: babysitter on June 01, 2014, 05:38:06 pmI don't think this is necessarily anything to do with polarity. The heat is in the spark itself where the gas is ionized. The electrodes get heated up by contact with the spark and their temperature depends on how well they can conduct away the heat.In a car spark plug the center electrode gets hottest because it is smaller and is less able to conduct the heat away. For this reason the center electrode is made negative so that it emits electrons, since electron emission is easier from hot surfaces (hence the heater in vacuum tubes).

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: June 02, 2014, 01:20:13 am
content: Quote from: IanB on June 01, 2014, 08:10:57 pmYeah, but in airplanes the spark polarity is reversed for every spark.

author: tautech
author_rank: Super Contributor
timestamp: June 02, 2014, 02:25:39 am
content: Its all about Joules. Total energy.But if it is for Auto use there are many factors to consider.Fuel octaneFuel typeCompression ratioBoost pressureRPMSpark plug styleMotorsport is the leading group for this knowledge, although it is not always shared in detail.

author: IanB
author_rank: Super Contributor
timestamp: June 02, 2014, 02:42:21 am
content: Quote from: CaptnYellowShirt on June 02, 2014, 01:20:13 amThis may be because the ignition system in aircraft is powered by magnetos and magnetos naturally produce AC.