Abstract
Research and/or Engineering Questions/Objective
Research on the utilisation of gas-to-liquid (GTL) naphtha in spark ignition (SI) engines is of high interest due to potential increased availability of GTL naphtha. With a high proportion of straight chain paraffins, GTL naphtha has a low octane rating, making it unsuitable to be directly used in SI engines. One potential solution to overcome the poor knocking performance is to enhance the gasoline blend stock by adding ethanol to compensate for the reduced octane of GTL naphtha. The objective of this research work is to assess the feasibility of using GTL naphtha as a blend component for future, modern SI engines. Single cylinder tests have been conducted to understand the emissions and full load power performance in SI engines.
Methodology
In this study, five GTL naphtha blends with up to approximately 24% GTL naphtha were formulated and tested in a single cylinder SI engine. The focus was to assess their gaseous and particulate emissions, and the full load performance including a comprehensive thermodynamic analysis to correlate engine results with fuel properties. An AVL state-of-art single cylinder engine with two configurations including boosted gasoline direct injection (GDI) and port fuel injection (PFI) configurations were used for fuel investigations. Typical New European Driving Cycle (NEDC) steady state operating points with engine speed ranging from 1000-2500 rpm and engine load ranging from 2-10 bar IMEP, and the full power curve with speed ranging from 1000 to 4500 rpm were tested. Boundary conditions, such as intake manifold pressure and temperature, exhaust back pressure, and fuel, coolant and oil temperature were precisely controlled to isolate the impact of fuel properties. Results were compared with those of a standard 95 RON fuel which meets the European gasoline specification EN228.
Results
Fuel blends containing GTL naphtha behaved like a traditional gasoline with regards to performance in a SI engine.
Limitations of this study
Tests were carried out in a single cylinder engine. More detailed chassis dynamometer and multi-cylinder engine tests are the next step to assess the feasibility of GTL naphtha for SI engines. Further work is needed to understand the impact under transient operation and cold start performance.
What does the paper offer that is new in the field including in comparison to other work by the authors?
This paper investigates in a systematic way using state of the art SI technology on how the anti-knock properties of ethanol can be used to mitigate the low octane of GTL naphtha
Conclusions
The preliminary results demonstrated the feasibility of using GTL naphtha blends in a spark ignition engine without compromising on engine performance or engine-out emission behaviour.
Key Words : GTL; Naphtha; Spark Ignition; Emissions