Emissions, Fuel Economy, and Performance of a Class 8 Conventional and Hybrid Truck

Emissions, fuel economy, and performance are determined over a light and a heavy driving cycle designed to represent the vehicles in-use driving patterns. The vehicles are 2010 class 8 Freightliner tractor trucks equipped with Cummins engines with Selective Catalytic Reduction and Diesel Particulate Filter emission control systems. The hybrid has lower carbon dioxide emissions, better fuel economy, and nitrogen oxide emissions statistically the same as the conventional. The CO emissions are well below the standards for both vehicles, but they are higher from the hybrid. The higher CO emissions for the hybrid are primarily related to the cooling of the Diesel Oxidation Catalyst (DOC) during the standard 20 minute key-off soak between repeats of the driving cycles. With a 1 minute key-off soak the CO emissions from the hybrid are negative. The relevance of higher hybrid CO emissions to in-use emissions is not clear since it is not known how often or how long the engine is off between deliveries on a typical day. The measured hybrid particulate emissions are statistically the same for the heavy cycle but higher for the light cycle. The higher PM for the hybrid may be related to the cooling of the DOC during the 20 minute key-off soak.

Performance is measured by determining the time to accelerate on the chassis dynamometer to 20 mph for each cycle. The hybrid takes longer to reach 20 mph and accelerates slower than the conventional.