Systematic optimization of ignition timing and spark plug heat range using the taguchi method for cleaner combustion in a four-stroke SI motorcycle engine
Keywords:
Ignition timing, Spark plug heat range, Taguchi method, Combustion optimization, Motorcycle emissionsAbstract
Improving combustion quality in small-displacement spark-ignition (SI) motorcycle engines is a key strategy for reducing exhaust emissions without compromising engine performance. This study presents a systematic optimization of ignition timing and spark plug heat range using the Taguchi L9 orthogonal array method to achieve cleaner and more stable combustion in a four-stroke SI motorcycle engine. Several ignition timing advance levels and spark plug heat grades were evaluated under controlled engine operating conditions. Exhaust gas emissions, including carbon monoxide (CO) and unburned hydrocarbons (HC), were measured using a calibrated gas analyzer and used as performance indicators for combustion quality. Statistical optimization based on signal-to-noise (S/N) ratio analysis and analysis of variance (ANOVA) was conducted to quantify the relative contribution of each ignition parameter to emission behavior and combustion efficiency. The results indicate that ignition timing exerts the dominant influence on incomplete combustion indicators, while the spark plug heat range plays a secondary but supportive role by affecting thermal dissipation and early flame kernel development; auxiliary ignition-related parameters were found to have comparatively minor contributions. An optimized combination of ignition timing advance and appropriate spark plug heat range led to a noticeable reduction in CO and HC emissions, accompanied by increased CO₂ formation, indicating more complete fuel oxidation without additional fuel input. These findings demonstrate that systematic ignition system tuning using the Taguchi method provides a practical and cost-effective approach for improving combustion cleanliness in existing motorcycle engines.
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