PREMIXED COMBUSTION IN A LIGHT DUTY COMPRESSION IGNITION ENGINE THROUGH FUEL AND INJECTION SYSTEM DESIGN: AN EXPERIMENTAL APPROACH

Abstract

Premixed combustion modes in compression ignition engines are studied as a promising solution to meet fuel economy and increasingly stringent emissions regulations. Nevertheless, PCCI combustion systems are not yet consolidated enough for practical applications due to their high complexity in terms of air-fuel charge preparation, combustion process control or due to the difficulties to extent the operating range. In this framework, this research is aimed to further investigation in the field of PCCI in order to provide additional information, from the fuel side and engine side, for an adequate comprehension of the phenomena and for practical applications. From the fuel side, this work focuses on providing an overview of the low cetane number (CN) oxy-fuel capabilities to improve both diesel and PCCI combustion in a research light-duty diesel engine. The effects of the cyclohexanone (chosen as representative of the low CN oxy-fuels) and diesel blends on the engine combustion are assessed, i.e. in terms of speed and load range and using PCCI and conventional engine control strategies (EGR, injection pressures, splitted injection, etc.). The results show that low CN oxy-fuels could act as enablers for PCCI combustion, outlining that the low CN and the oxygen content works together to control the smoke emissions. Moreover, the cyclohexanone can be produced from lignin and thus has the potential to be renewable. From the engine side, the study is aimed to investigate the effect of a specially designed port fuel injection (PFI) system on performance and emissions using n-heptane, as representative of diesel fuel for direct injection, and n-heptane or ethanol as PFI fuel. The results highlight that ethanol (as a low CN fuel) exhibits improved performance in terms of premixed charge formation, combustion control and smoke emissions without evident reduction in fuel efficiency.