Perfect spark plug?

[454Casull]

Yep, I decided TiB2 would be better as an electrode material. Last I heard it resisted oxidation under 700C very well.

[quaddriver]

Originally Posted by 454Casull

Assuming an infinitely powerful ignition distribution system, what gap would you use? What electrode positioning would you use (extended, surface-fire, Halo-type, standard)? What electrode material would you use? What electrode plating would you use, if any? What insulation would you use? What shell material would you use?

Also, do you believe in that HotWires stuff?
Link

I would probably use a surface-fire plug /w a gap of 0.1-0.5", an electrode material of ELKONITE 2050C, iridium plating (because I don't know the inertness of the material), and probably a Ceralloy 418 insulator.

ELKONITE 2050C - 0.0297 ohm-mm²/m electrical resistivity, 330W/m-K thermal conductivity, up to 3400C melting point.
Ceralloy 418 - low thermal expansion, high dielectric constant, 250W/m-K thermal conductivity

Id probably use the one that lit the mix with the least voltage and caused less hits on the KS. any more is waste.

[Evil Result]

any of you here who might have cut back the ground electrode on there J gap spark plug notice more power, better responce, or better gas mileage?

[SaabJohan]

Originally Posted by 454Casull

Yep, I decided TiB2 would be better as an electrode material. Last I heard it resisted oxidation under 700C very well.

Use one of the platinum group metals instead. Has lower electrical resistivity and are one of the most inert metals at higher temps. They have also excellent strength at high temperatures, for exemple iridum based superalloys are one of the most heat resistant alloys, can be used at temps above 2000 degC.

Their price do however beat almost anything else on the market.

[454Casull]

Originally Posted by SaabJohan

Use one of the platinum group metals instead. Has lower electrical resistivity and are one of the most inert metals at higher temps. They have also excellent strength at high temperatures, for exemple iridum based superalloys are one of the most heat resistant alloys, can be used at temps above 2000 degC.

Their price do however beat almost anything else on the market.

I'll agree that oxidation of TiB2 is present at very high temperatures, but high strength at high temperatures is what TiB2 does well. Besides, with the high resistance of the spark cabling, and the REALLY high resistance of the air gap, a few more ohms of resistance won't matter. TiB2 is nominally conductive anyway.

[SaabJohan]

Originally Posted by 454Casull

I'll agree that oxidation of TiB2 is present at very high temperatures, but high strength at high temperatures is what TiB2 does well. Besides, with the high resistance of the spark cabling, and the REALLY high resistance of the air gap, a few more ohms of resistance won't matter. TiB2 is nominally conductive anyway.

The platinum metals do already have a high strength in high temperatures so there is really no improvement. Ceramics does also break before their ultimate strength (but they are good at compressive stress). But I don't think the strength is so important (it's more about oxidation resistance). The module of elasticity is also about the same for both materials.

[ivymike1031]

Perhaps this will spark some more discussion:

railplugs

http://www.netl.doe.gov/scng/project.../are41334.html
http://www4.ncsu.edu:8030/~mfhabel/e497/railplug.html

Sounds like a nifty way to light off a lean charge, if they get 'em
tuned well enough. I'm not so sure that they make sense for near-
stoich applications.

[-Josh-]

What would kick ass, is if combustion worked like it does in Diesel engines. There would be no spark plugs, just compression.