Vehicle Demonstration of Naphtha Fuel Achieving Both High Efficiency and Drivability with EURO6 Engine-Out NOx Emission

Demand for transport energy is growing but this growth is skewed heavily toward commercial transport, such as, heavy road, aviation, marine and rail which uses heavier fuels like diesel and kerosene. This is likely to lead to an abundance and easy availability of lighter fractions like naphtha, which is the product of the initial distillation of crude oil. Naphtha will also require lower energy to produce and hence will have a lower CO2 impact compared to diesel or gasoline. It would be desirable to develop engine combustion systems that could run on naphtha. Many recent studies have shown that running compression ignition engines on very low Cetane fuels, which are very similar to naphtha in their auto-ignition behavior, offers the prospect of developing very efficient, clean, simple and cheap engine combustion systems. Significant development work would be required before such systems could power practical vehicles. Naphtha has much lower Cetane compared to a conventional European diesel fuel. The aim of this study is to investigate if and how an existing modern diesel engine could be run on low Cetane fuels in general and naphtha in particular. Extensive single-cylinder engine tests using different low Cetane fuels showed that the engine could be run on narrow-cut naphtha with a derived Cetane (DCN) number of 38, at all relevant speed and load conditions, while meeting or exceeding the efficiency and emissions requirements. Based on these engine studies, a downsized four-cylinder 1.6 liter diesel engine adapted with piezoelectric fuel injectors, EGR cooling and two-stage air boosting system was installed in a demonstration vehicle equipped with an on-board combustion control system. The vehicle was successfully run under cold NEDC (New European Driving Cycle) operation at high efficiency with good transient operation and acceptable noise levels while achieving engine-out NOx emission below EURO6 levels using naphtha. Moreover, engine-out PM (particulate matter) emissions were lower than those generated with conventional diesel fuel on the base engine. This work demonstrated that a modern diesel vehicle can run at high efficiency and low noise and emissions on a simple fuel that requires little processing in the refinery compared to the diesel fuel and will be easily available in the future.