Fuel Economy Potential of Partially Premixed Compression Ignition (PPCI) Combustion with Naphtha Fuel 2013-01-2701

Recent research [21] has shown that the compression ignition concept where very low cetane fuels (RON between 70 and 85) are run in compression ignition (CI) mode has several advantages. The engine will be at least as efficient and clean as the current diesel engines but will have a less complicated after-treatment system. The optimum fuel will be less processed and therefore simpler to make compared to current gasoline or diesel fuels. Naphtha, which is a product of the initial distillation of petroleum, is one such fuel. It provides a path to mitigate the global demand imbalance between heavier and lighter fuels that is otherwise projected. Since naphtha requires much less processing in the refinery than either gasoline or diesel [23], there is an additional benefit in terms of well-to-wheel CO₂ emissions and overall energy consumed.

Partially premixed charge compression ignition combustion with such a low cetane fuel has usually been investigated with a diesel engine base. In our recent publication [21], we have demonstrated that Naphtha, an intermediate refinery stream, can fuel a modern Diesel vehicle without compromising comfort, drivability, emissions or power requirements. It can also be considered as a way of increasing the efficiency of a Gasoline powertrain system. In our previous paper [15], we demonstrated a reduction in fuel consumption in a SI engine with a compression ratio (CR) of 12 when it was run in partially premixed combustion mode using naphtha. In this work, we developed more optimized combustion chamber design to improve idle and light load combustion stability. With a newly designed 14:1 CR piston and light naphtha, we achieved 26% average fuel consumption reduction over a range of part load operating points which represents federal test procedure (FTP) city cycle, compared to running the base SI engine on gasoline while engine out NOx & PM emissions were within Tier II Bin5 level. Load range windows for partially premixed combustion operation were identified without compromising emission and pressure rise rate thresholds. Lastly, stable naphtha combustion was also demonstrated at cold condition. Therefore, this work shows another way of developing a highly efficient fuel and engine system starting from a SI engine platform and optimized synergistically using naphtha fuel.