Emission Performance of Low Cetane Naphtha as Drop-In Fuel on a Multi-Cylinder Heavy-Duty Diesel Engine and Aftertreatment System

Greenhouse gas regulations and global economic growth are expected to drive a future demand shift towards diesel fuel in the transportation sector. This may create a market opportunity for cost-effective fuels in the light distillate range if they can be burned as efficiently and cleanly as diesel fuel. In this study, the emission performance of a low cetane number, low research octane number naphtha (CN 34, RON 56) was examined on a production 6-cylinder heavy-duty on-highway truck engine and aftertreatment system. Using only production hardware, both the engine-out and tailpipe emissions were examined during the heavy-duty emission testing cycles using naphtha and ultra-low-sulfur diesel (ULSD) fuels. Without any modifications to the hardware and software, the tailpipe emissions were comparable when using either naphtha or ULSD on the heavy duty test cycles. Overall lower CO₂ emissions and fuel consumption were measured for naphtha due in part to its higher heating value and higher hydrogen to carbon ratio. Engine-out and tailpipe NOx emissions were lower for naphtha, and measured PM emissions were also lower due to naphtha’s higher volatility and lower aromatic content compared to ULSD. To help assess the potential impact on diesel particulate filter design and operation, engine-out PM samples were collected and characterized at a steady-state mid-speed, mid-load operating point. A significant reduction in elemental carbon in PM samples was observed for naphtha fuel, and similar oxidation rates and peak oxidation temperatures were measured for the PM from both fuels.