Comparing the Performance of GTL/ULSD Blends in Older and Newer Diesel Passenger Cars

Gas-to-Liquids (GTL) is a liquid diesel fuel produced from natural gas, which may have certain attributes different from conventional ultra low sulfur diesel (ULSD). In this investigation, GTL, ULSD, and their blends of 20% and 50% GTL in ULSD were tested in an older Mercedes C Class (MY1999, Euro 2) and a newer Opel Astra (MY2006, Euro 4) diesel vehicle to evaluate the performance in terms of fuel consumption and emissions. Each vehicle was pre-conditioned on-road with one tank full of test fuel before actual testing in a chassis dynamometer facility. Both vehicles were calibrated for European emission standards and operation, and they were not re-calibrated for the fuel tests at Argonne National Laboratory (ANL). In the two-vehicle EPA FTP-75, US06, and Highway drive-cycle tests, the emissions of carbon dioxide on a per-mile basis (g/mi) from all GTL-containing fuels were significantly lower than those from the ULSD. Similarly, the exhaust emissions of NO_x, were mostly lower in both vehicles but without a clear trend of decreasing NO_x emissions with increasing GTL content in the blend. PM emissions from the diesel particulate filter (DPF) - equipped Opel Astra were all less than 3 mg/mi for all the drive cycles and were extremely challenging to measure by using the conventional gravimetric method with a full-dilution tunnel. During the Highway drive-cycle testing, the DPF underwent regeneration with both the ULSD and 20% GTL in ULSD blend, which resulted in drastic increases in PM, NO_x and CO₂ emissions.