Abstract
Recent work has demonstrated the potential of gasoline-like fuels to reduce NOx and particulate emissions when used in compression ignition engines. In this context, straight-run naphtha, a refinery stream directly derived from the atmospheric crude oil distillation process, has been identified as a highly valuable fuel. In addition, thanks to its higher H/C ratio and energy content (LHV) compared to diesel, CO2 benefits are also expected when using naphtha in such engines.
The purpose of this study is to investigate the potential of naphtha fuel on a light duty single-cylinder compression-ignition engine as well as the minimum required hardware modifications needed to properly run this fuel. Tests on the engine are conducted within two different compression ratios CR16 (stock piston) and CR17.5. The hydraulic flow rate of the nozzle was increased for naphtha to compensate its lower fuel density vs. diesel. The results were compared to those obtained with a reference €5 diesel engine with CR16.They show that the maximum torque and power of the diesel baseline were achieved with naphtha using both pistons. At part load, naphtha shows relatively lower soot emissions for the same levels of NOX and noise. Compared to diesel, CO2 emissions are reduced by approximately 9% with CR16 and 8% with CR17.5 on the WLTC cycle. Compared to CR17, CR16 enables an earlier combustion phasing, as well as a higher degree of fuel stratification. This leads to lower HC and CO emissions at even low loads and better fuel consumption with CR16.
Some WLTC cycle estimations have demonstrated that, with naphtha fuel, the engine can achieve Euro 6 emission regulations with high efficiency, without increasing the cost of the after treatment system. Even if HC and CO emissions are higher with naphtha for both CRs at low load conditions compared to diesel, these emissions can be handled by using a standard DOC.