Fyi
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Safety Car
Joined: May 2003
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From: Ocean Township NJ
F y i
While the following data may not be exact for a specific engine, it does clearly show the trends that all engines follow. Further, remember that leaner mixtures require higher firing voltages than richer mixtures.The calculated values are for air only and do not include fuel ratio effects. Nor do they include plug electrode materials, tip geometry, and accumulated deposits.
Given a compression ratio of 11.4 and a trapped compression ratio of 9.0, inlet temperature of 100F and inlet pressure of 1 Bar:
If the plug fires at -45 deg BTC the cylinder Temp will be 399F , Press will be 66psi
Required firing voltages at various gaps: .050" = 12.1kV, .080" = 18.1kV, .100" =22.1kV
If the plug fires at -35 deg BTC, the cylinder Temp will be 496F, Press will be 97psi
Required firing voltages at various gaps: .050" = 15.3kV, .080" = 23.2kV, .100" =28.3kV
If the plug fires at -25 deg BTC, the cylinder Temp will be 609F, Press will be 144psi
Required firing voltages at various gaps: .050" = 19.6kV, .080" = 29.8kV, .100" =36.5kV
As can be seen, larger gaps require higher firing voltages. But retarded ignition timing also requires higher firing voltages.
The worst scenario is a high compression engine, with large plug gaps and retarded ignition.
Given a compression ratio of 11.4 and a trapped compression ratio of 9.0, inlet temperature of 100F and inlet pressure of 1 Bar:
If the plug fires at -45 deg BTC the cylinder Temp will be 399F , Press will be 66psi
Required firing voltages at various gaps: .050" = 12.1kV, .080" = 18.1kV, .100" =22.1kV
If the plug fires at -35 deg BTC, the cylinder Temp will be 496F, Press will be 97psi
Required firing voltages at various gaps: .050" = 15.3kV, .080" = 23.2kV, .100" =28.3kV
If the plug fires at -25 deg BTC, the cylinder Temp will be 609F, Press will be 144psi
Required firing voltages at various gaps: .050" = 19.6kV, .080" = 29.8kV, .100" =36.5kV
As can be seen, larger gaps require higher firing voltages. But retarded ignition timing also requires higher firing voltages.
The worst scenario is a high compression engine, with large plug gaps and retarded ignition.
Last edited by 65tripleblack; Apr 1, 2011 at 10:59 AM.
