Impact of Aggressive and Moderate Driving Intensity on Vehicle Air–Fuel Ratio Stability

Ab Hamid, Mohamad Norsyafiq; Ismail, Muhammad Yusri Bin; Badrulhisam, Najmi Haziq · 2026 · Crossref

DOI: 10.31436/iiumej.v27i2.4062

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Summary

This study investigates the impact of aggressive versus moderate driving behaviors on engine air–fuel ratio (AFR) stability, addressing a gap in literature regarding real-world transient combustion dynamics. While prior research often focuses on steady-state conditions or laboratory settings, this work aims to quantify how driver-induced acceleration and braking patterns affect AFR fluctuations, combustion efficiency, and potential emissions using real-time On-Board Diagnostics (OBD-II) data. The experimental design utilized a 2008 passenger car equipped with a 1.8-liter gasoline V6 engine and automatic transmission. Data was collected via an OBD-II scanner at a 1 Hz sampling rate during three repeated runs for each driving style along an 11.7 km urban-suburban route. Aggressive driving was defined by speeds between 80–100 km/h with frequent acceleration and deceleration, while moderate driving involved steady speeds of 50–80 km/h with minimal braking. To analyze the non-stationary AFR time-series data, the researchers employed Continuous Wavelet Transform (CWT) to derive Wavelet Power Spectrum (WPS) and Global Wavelet Spectrum (GWS) metrics, alongside statistical boxplot and frequency distribution analyses. Results demonstrated significant differences in AFR stability between the two driving styles. Aggressive driving caused greater AFR instability, characterized by rapid oscillations ranging from 13.0 to 18.0 and extreme rich outliers near 12.5. The GWS peaks for aggressive driving reached approximately 40 units, double the 20 units observed in moderate driving. Furthermore, aggressive driving spent more time in fuel-rich regions (12–17% frequency in mid-range bins) compared to moderate driving (5–14%). In contrast, moderate driving maintained a narrower, more stable AFR distribution (14.0–17.5), with a higher proportion of leaner readings (~36% in the 15.3–16.4 range) closer to the stoichiometric value of 14.7. Statistical analysis confirmed that while both styles operated within similar AFR boundaries, aggressive driving exhibited a higher incidence of extreme-rich excursions associated with incomplete combustion. The findings conclude that driving intensity significantly influences AFR stability, with moderate driving promoting cleaner and more efficient engine operation. The instability observed during aggressive driving suggests increased fuel consumption and higher emissions of hydrocarbons and carbon monoxide due to rich mixture excursions. Conversely, the stability of moderate driving supports improved combustion efficiency and catalytic converter performance. These results provide empirical evidence for the benefits of eco-driving practices and offer data-driven insights for developing adaptive vehicle control algorithms and driver behavior recognition systems aimed at enhancing energy efficiency and reducing environmental impact in real-world conditions.

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• aggressive driving