Improved Analytically Derived CO <sub>2</sub> Prediction of Medium Duty Chassis-Certified Vehicles

Abstract

<div class="section abstract"><div class="htmlview paragraph">Medium duty vehicles come in many design variations, which makes testing them all for CO<sub>2</sub> impractical. As a result there are multiple ways of reporting CO<sub>2</sub> emissions. Actual tests may be performed, data substitution may be used, or CO<sub>2</sub> values may be estimated using an analytical correction. The correction accounts for variations in road load force coefficients (f<sub>0</sub>, f<sub>1</sub>, f<sub>2</sub>), weight, and axle ratio. The EPA Analytically Derived CO<sub>2</sub> 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 CO<sub>2</sub> 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.</div></div>