Abstract
Research Objective
Gasoline Compression Ignition (GCI) engine showed the potential to match the efficiency of compression ignition (CI) engines with reduced emission of NOx and soot. The objective of this work is to understand the influence on gasoline combustion of different injector parameters such as umbrella angle, number of injection and injection timing when a 95 RON gasoline is direct injected in a commercial Diesel engine.
Methodology
Experiments were performed in a single-cylinder Diesel engine fuelled with direct-injected 95 RON gasoline at 2 bar IMEP. Engine speed was set to 1500 rpm. Intake pressure was set to 1 bar in order to investigate typical low load operating conditions in which turbocharger can not supply extra pressure at the intake and the intake temperature was adjusted to enable the autoignition of gasoline. Two different injectors with a wide (156°) and a narrow (90°) umbrella angle were tested. For each injector, experiments were carried out with a single and a double injection strategy over a wide range of injection timings.
Results
The behavior of the two injectors was compared in terms of engine performances and pollutant emission. Early injection timings were necessary to enable gasoline autoignition. Results showed that a wide umbrella angle can limit the advance in injection timing because of part of the fuel is directed towards the squish region and do not participate at the combustion event. A narrower injection angle allowed to better concentrate the fuel inside the piston head bowl: the autoignition of gasoline originated from fuel-air mixture characterized by richer distribution of the local equivalence-ratio, improving combustion efficiency and reducing the formation of HC and CO while maintaining low emission of NOx. However, such advanced injection timings led gasoline to autoignite under premixed conditions characterized by an intense heat release rate. For both injectors, a double injection strategy was employed to introduce the sufficient fuel stratification necessary to reduce the heat release rate.
Limitations
Because of the high octane number of commercial gasoline, an electrical heater was added to increase the intake air temperature up to 205°C. Such intake temperatures are not available on a current car environment.
What does the paper offer that is new in the field in comparison to other works of the author
The analysis and comparison between a typical diesel injector and an injector with a narrower umbrella angle presented in this paper is new for GCI engine fuelled with commercial 95 RON gasoline at low load operations.
Conclusion
For low load operation of GCI engine, the use of an injector with a narrow umbrella angle presented advantages if compared to a typical wider Diesel injector in terms of combustion efficiency and pollutant emission of HC and CO.
Key Words : GCI, Injection Strategy, Low Load, LTC