Improved Analytically Derived CO ₂ Prediction of Medium Duty Chassis-Certified Vehicles 2019-01-0311

Medium duty vehicles come in many design variations, which makes testing them all for CO₂ impractical. As a result there are multiple ways of reporting CO₂ emissions. Actual tests may be performed, data substitution may be used, or CO₂ values may be estimated using an analytical correction. The correction accounts for variations in road load force coefficients (f₀, f₁, f₂), weight, and axle ratio. The EPA Analytically Derived CO₂ equation (EPA ADC) was defined using a limited set of historical data. The prediction error is shown to be ±130 g/mile and the sensitivities to design variables are found to be incorrect. Since the absolute CO₂ is between 500 and 1,000 g/mi, the equation has limited usefulness. Previous work on light duty vehicles has demonstrated a linear relationship between vehicle fuel consumption, powertrain properties and total vehicle work. This relationship improves the accuracy and avoids co-linearity and non-orthogonality of the input variables. The proposed equation reduces the prediction error to ± 35 g/mile and gives correct sensitivities to design parameters.