Gas To Liquid (GTL) fuels synthesized from natural gas are known as clean fuels. Therefore, GTL fuels have been expected to be a promising option that can reduce the NOx and PM emissions from diesel engines and contribute to the energy security.
In this study, in order to clarify the emission reduction potentials, the improvement of DI diesel engine and aftertreatment systems were investigated by utilizing GTL fuels characteristics.
To achieve a further reduction of both NOx and PM emissions, the combustion chamber, injection pattern and EGR calibration were modified. From the results of tests, the engine out NOx emissions were reduced to the Euro 6 regulation level and in parallel the expected deteriorations of HC emission and fuel consumption were suppressed because of the characteristics of high cetane number and zero poly-aromatics hydrocarbons.
Additionally, an aftertreatment system was optimized to GTL fuel in order to improve NOx conversion efficiency. The diesel particulate and NOx reduction system (DPNR) can reduce NOx and PM simultaneously. However, the DPNR catalyst deteriorates due to sulfur poisoning and by high temperature of desulfation control. As GTL fuels have zero sulfur, the DPNR catalyst could be designed without having to consider desulfation performance. The results of vehicle testing indicate that emissions were significantly reduced and NOx conversion efficiency was maintained even after a mileage accumulation test. These modifications enable to realize ultra low emissions as good as a gasoline-fueled vehicle.
These investigation results clarify that combination of the GTL fuel as a clean fuel and the modifications of engine system have potential to reduce emissions and to improve durability performance of aftertreatment system whilst keeping the features of diesel engines such as low CO2 emission.