Misfire detection in bi-fuel engines operating on compressed natural gas (CNG) and gasoline mode presents significant challenges due to inherent differences in combustion characteristics: ignition dynamics and fuel properties. Accurate detection is essential for minimizing the emissions, engine performance, and ensuring regulatory compliance. A fundamental parameter in crankshaft speed fluctuation-based misfire detection is segment time selection, which directly influences detection fidelity, false positives, and false negatives. Given CNG’s slower combustion kinetics and delayed flame propagation, it necessitates a delayed segment initiation and an extended segment duration, whereas gasoline characterized by faster combustion, permits earlier segment initiation and a reduced segment duration. Optimal segment timing is determined by analyzing engine roughness, minimizing signal-to-noise ratio (SNR), and eliminating cylinder overlap, while also incorporating flywheel manufacturing tolerances. Engine roughness baselines must be systematically tuned across the full operational spectrum-from idle to maximum speed and from zero to 90% of maximum torque-to maintain consistency and mitigate inter-cylinder roughness deviations. Given the distinct combustion dynamics of bi-fuel engines, roughness threshold calculations must be fuel-specific, as CNG inherently exhibits greater roughness than gasoline. These thresholds are derived from the empirical data obtained through controlled manual misfire simulations. External variables such as road-induced vibrations and abrupt load changes can exacerbate roughness fluctuations, increasing the likelihood of misdetection. Persistent roughness elevation in a specific cylinder can induce excessive exhaust temperatures, posing a risk to catalytic converter integrity. To mitigate this, the system must implement immediate cylinder-specific fuel cut-off and activate driver alert mechanisms, ensuring catalyst protection and compliance with OBD II regulations, which remain fuel-agnostic in misfire detection criteria. This research paper brings out the before mentioned issues in misfire detection in CNG and Gasoline engine.
Keywords: Bi-fuel engines, Misfire detection, Segment time selection, Engine roughness calibration, Catalytic converter protection, OBD II compliance