Spark plugs utilizing a J-wire electrode are standard in most automotive engines and have been for decades. However, innumerable alternative spark plug designs have been introduced. This paper examines the potential benefit of one particular alternative electrode geometry in a high-performance automotive engine. The alternative spark plug that is investigated is a commercially available aftermarket unit. The testing included detailed analysis of both brake and indicated parameters including MEP and burn rates. Testing was conducted under both steady state and transient conditions, and encompassed multiple induction systems and test fuels including E85. The test engine was a commercially available high performance aftermarket engine assembly intended for motorsports.
This paper includes the optimal settings for ignition timing and lambda and the process by which those values were determined. The combustion analysis shows the alternative spark plug electrode resulted in an increased early burn rate, which in turn lead to an overall advancing of the combustion phasing. To better decouple combustion phasing effects from test to test variation on brake output parameters, an empirical model is developed and exercised. The model describes the expected change in brake output resulting from the shift in combustion phasing induced by the alternative spark plug geometry.